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Title: A Practical Manual of the Collodion Process, Giving in Detail a Method For Producing Positive and Negative Pictures on Glass and Paper.
Author: Humphrey, S. D. (Samuel Dwight)
Language: English
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Text emphasis is denoted as _Italic_ and =Bold=. Whole and fractional
parts of numbers as 123-4/5.



                            HUMPHREY'S JOURNAL

                                  OF THE

                   DAGUERREOTYPE AND PHOTOGRAPHIC ARTS.

                                ~~~~~~~~~~

The above-named Publication is well known as the best and most valuable
one devoted to the Photographic Science in this country. Humphrey's
Journal made its first appearance Nov. 1st, 1850, and consequently is the
first and oldest serial offered to the Photographic world.

The art of producing Portraits and Landscapes by means of Light has
recently taken a new and enlivening impulse, which will in all probability
lead to important and interesting results. No practical Daguerreotypist,
Photographer, or amateur should be without the means at hand for securing
all of the information upon this subject. Each should be ready to
receive and apply the improvements as they may be developed. In order to
accomplish this, it is a matter of great importance to the Practitioner
or Experimenter that he should have a _reliable_ medium through which he
can obtain _information_. In what source can the inquirer better place
his confidence than in a regular Journal, whose editor is literally a
_practical_ person, and familiar with the manipulations necessary for
producing Portraits upon "_Daguerreotype Plates_," and upon glass and
paper? Such is the conductor of Humphrey's Journal.

This Journal is published once every two weeks, and contains all the
improvements relating to the Art, and is the only American Journal
whose editor is _practically acquainted_ with the process for producing
_Daguerreotypes_. _Ambrotypes_, and _Photographs_ The first No. of Vol.
VIII is dated May 1st, 1856. The terms (Two Dollars per annum) are
trifling compared with the vast amount of information furnished.

There are several societies recently established in Europe composed of
learned and scientific men, who are in every way engaged in investigating
the Science, and we may look for improvement from that quarter, as well as
from our numerous resources at home. In the former case our facilities for
early and reliable information cannot well be surpassed.

Ambrotypes.--_Humphrey's Journal_ contains everything novel which appears
upon this subject, and has already presented more new, important; and
original matter than can be found in any other place.

Many are the letters we have received during the term of the last volume,
in which the writer has stated that a single number of Humphrey's Journal
has contained information of more value to him than "several times the
amount paid for the entire volume."

Our resources have grown up around us, and our facilities for procuring,
as well as distributing, all such facts and improvements as will benefit
as well as instruct all who have the progress of the Art at heart, are as
ample as they can well be made.

The future volumes will be abundantly furnished with original writings
from persons of standing in the scientific world; and the practical
Photographer will here find a full account of such improvements as may
from time to time develope themselves.

From the Editor's long practical experience in the Heliographic Science,
he will be enabled to present the subject in a plain, clear and concise
manner.

Read what the Editors say of Humphrey's Journal:--

"We have received a copy of a valuable Journal (Humphrey's) published in
New York, which has reached the 18th number of Vol. VI. ... We now have
the pleasure of quoting from our transatlantic coadjutor."--_Liverpool
Photographic Jour._

"Humphrey's Journal is practical as Well as scientific in
character."--_American Journal of Science and Arts._

"It treats the subject knowingly, and with force."--_New York Tribune._

"It is both a popular and interesting publication."--_Mechanics'
Magazine._

"It is highly useful to all who practice 'shadow catching.'"--_Ohio State
Journal._

"The work is neatly gotten up, and contains many interesting varieties in
this new field of science."--_Times._

"It should be hailed and encouraged, not only by Daguerreotypists
themselves, but by every lover of Science and Art."--_The Democrat._

"We cannot too strongly urge all artists, and those persons who feel an
interest in the Heliographic Arts and Sciences, to take a copy of the
work."--_Sentinel._

"It is indicative of talent worthy of the important Art it is designed to
elevate."--_American._

"This Art is entitled to its own organ, which could not have
fallen into better hands than those of the editor of Humphrey's
Journal."--_Transcript._

"It is a scientific work of interest and usefulness."--_Star of the North._

"This Journal answers many points heretofore regarded as
inexplicable."--_Hudson River Chronicle._

"It is rich with interest."--_North American._

"It contains all the 'Improvements.'"--_Delta._

"It teaches us how to take our own portraits."--_Bee._

"It will cultivate a taste for Daguerreotypes."--_Commercial Advertiser._

"It should be in the hands of all."--_Reveille._

"It is the Daguerreotypist's friend."--_London News._

"It should be found in every library."--_Evening Journal._


_From some of our old subscribers._

"Humphrey's Journal has been the means of saving much time and money, for
by its instruction I have been enabled to produce some of the finest Paper
Pictures I have ever seen." W. P.

"Don't fail to send me the Journal, for I would not be without it for
_five_ times the amount of subscription. It is the only publication I can
_depend_ upon." A. G. R.

"Your treatment of the humbugs and humbugging members of the profession,
is of the most valuable importance to us practical Daguerreians. Go on.
God speed! Here is the amount for the renewal of my subscription." E. F. S.

"How can any Operator afford to be without it?" L. L. H.

"Here is five dollars: send me Humphrey's Journal to this amount. I will
not be without it." M. S.

"It is my best friend." J. E. W.

We might quote like commendatory extracts enough to more than ten times
fill this page.

Humphrey's Journal contains 16 octavo pages of reading matter.


TERMS.

  One copy per annum, in advance     $2 00
  Three copies,  do.       do.        5 00
  Six copies,    do.       do.        9 00

The thousands who read it cannot be induced to remain without it. All who
desire to keep up with the improvements should subscribe for a copy.

Subscription price Two Dollars per year.

Don't fail to become a subscriber. Address

                                       =S. D, HUMPHREY,=
                                             NEW YORK.
  [_Office, 37 Lispenard Street_]



                                    A
                             PRACTICAL MANUAL
                                  OF THE
                            COLLODION PROCESS,
                 GIVING IN DETAIL A METHOD FOR PRODUCING
                          POSITIVE AND NEGATIVE

                      =Pictures on Glass and Paper.=


                               AMBROTYPES.


                            PRINTING PROCESS.

                                  ALSO,

                   PATENTS FOR THE COLLODION PROCESSES;

MELAINOTYPES--PHOTOGRAPHS IN OIL--ALBUMENIZED COLLODION--CUTTING'S PATENTS
    AND CORRESPONDENCE.--SPECIFICATION'S OF ALL THE FOREGOING, GIVING
                           EACH PROCESS ENTIRE.


               THIRD EDITION, REVISED AND GREATLY ENLARGED.

                            By S. D. HUMPHREY.



                                NEW YORK:

                        HUMPHREY'S JOURNAL PRINT,

                           37 LISPENARD STREET.

                                  1857.


Entered according to Act of Congress, in the year 1857, by S. D. HUMPHREY,
In the Clerk's Office of the District Court of the United States for the
Southern District of New York.



                      PREFACE TO THE THIRD EDITION.

                                ~~~~~~~~~~


The rapid and unexpected sale of the entire second edition of this Manual
has induced the author to lay the Third Edition before the Public.
Although but little time has elapsed since the second, yet there have been
some new developments which it has been thought best to give, as conducive
to the interests of the practitioner. The manipulations have been given
somewhat more in detail than in the Second Edition.

All that would have a tendency to confuse the reader has been carefully
avoided, and only the plain methods for operating laid down. The work is
intended for the beginner in the glass process of producing Heliographic
pictures.

                                                                  S. D. H.

  New York, _February 1st, 1857_.



                      PREFACE TO THE FIRST EDITION.

                                ~~~~~~~~~~


The object of this little Manual is to present, in as plain, clear and
concise a manner as possible, the _practice_ of a Collodion Process. This
beautiful acquisition to a "sun-pencilling" was first given to the public
by Mr. Frederick Scott Archer, an English gentleman, who alone is entitled
to the credit, and deserves the esteem of every lover and practitioner of
the Art, for his liberality in _giving_ it to the world.

The Process here presented has never before appeared in print, and has
been practised with the most eminent success by those who have been
enabled to adopt it.

All reference to the various systems or methods of manipulation, by the
thousands of practitioners, has been excluded, and one Process given. I
conceived that this was the better plan to adopt, thus leaving the mind of
the learner free from confusion, and pointing out one course, which, if
carefully followed, will produce good and pleasing results.

I have also presented a list of all Patents upon the Collodion Process;
this will give all an opportunity of choosing their own course in regard
to the respect they may conceive to be due to such Patent Rights.

                                                                  S. D. H.



                                CONTENTS.

                                ~~~~~~~~~~



PART I.


CHAPTER I.

  Introduction--Light--Solar Spectrum--Decomposition of Light--Light--Heat
  and Actinism--Blue Paper and Color for the Walls of
  the Operating Room--Proportions of Light, Heat and Actinism
  composing a Sunbeam--Refraction--Reflection--Lenses--Copying--Spherical
  Aberration--Chromatic Aberration 13

CHAPTER II.

  Camera--Arrangement of Lenses--Camera Tubes--Camera Boxes,
  Bellows, and Copying--Camera Stands--Head Rests--Cleaning
  Vice--Nitrate Bath--Leveling Stands--Printing Frames--Collodion
  Vials 26



PART II.

=Practical Hints on Photographic Chemistry.=


CHAPTER III.

  Soluble Cotton--Manipulation--Plain Collodion--Bromo-Iodized Collodion
  for Positives--Ditto for Negatives--Solution of Bromide and
  Iodide of Potassium and Silver--Double Iodide of Potassium and
  Silver--Developing Solution--Fixing the Solution--Brightening
  and Finishing the Image--Photographic Chemicals 41



PART III.

=Practical Details of the Positive or Ambrotype Process.=


CHAPTER IV.

  Lewis's Patent Vices for Holding the Glass--Cleaning and Drying the
  Glass--Coating--Exposure in the Camera--Developing--Fixing or
  Brightening--Backing up, &c. 129


PART IV.

=Practical Details of the Negative Process.=


CHAPTER V.

  Negative Process--Soluble Cotton--Plain Collodion--Developing
  Solution--Re-Developing Solution--Fixing the Image--Finishing the
  Image--Nitrate of Silver Bath 143



PART V.

=Practical Details of the Printing Process.=


CHAPTER VI.

  Printing Process--Salting Paper--Silvering Paper--Printing the
  Positive--Fixing and Coloring Bath--Mounting the Positive--Facts
  worth Knowing 151


CHAPTER VII.

  Helio Process.--An Entire Process for Producing Collodion Positives
  and Negatives with one Bath, and in much less time than by any
  other known Process: by Helio--Photographic Patents 164

CHAPTER VIII.

  The Collodio-Albumen Process in Detail 190


CHAPTER IX.

  On a Mode of Printing Enlarged and Reduced Positives, Transparencies,
  &c., from Collodion Negatives--On the Use of Alcohol for
  Sensitizing Paper--Recovery of Silver from Waste Solutions,--from
  the Black Deposit of Hypo Baths, &c.--The Salting and Albumenizing
  Paper--On the Use of Test Papers--Comparison of
  British and French Weights and Measures 191



CHAPTER I.

LIGHT--SOLAR SPECTRUM--DECOMPOSITION OF LIGHT--LIGHT, HEAT AND
ACTINISM--BLUE PAPER AND COLOR FOR THE WALLS OF THE OPERATING
ROOM--PROPORTIONS OF LIGHT, HEAT AND ACTINISM, COMPOSING A
SUN-BEAM--REFRACTION--REFLECTION--LENSES--COPYING--SPHERICAL
ABERRATION--CHROMATIC ABERRATION.


It has been well observed by an able writer, that it is Impossible to
trace the path of a sunbeam through our atmosphere without feeling a
desire to know its nature, by what power it traverses the immensity of
space, and the Various modifications it undergoes at the surfaces and the
interior of terrestrial substances.

Light is white and colorless, as long as it does not come in contact
with matter. When in apposition with anybody it suffers variable degrees
of decomposition, resulting in color, as, by reflection, dispersion,
refraction and unequal absorption.

To Sir I. Newton the world is indebted for proving the compound nature
of a ray of white light emitted from the sun. The object of this work is
not to engage in an extended theory upon the subject of light, but to
recur only to some points-of more particular interest to the photographic
operator.

[Sidenote: PRISM, SOLAR SPECTRUM.]

The decomposition of a beam of light can be noticed by exposing it to a
prism. If, in a dark room, a beam of light be admitted through a small
hole in a shutter 7 it will form a white round spot upon the place where
it falls. If a triangular prism of glass be placed on the inside of the
dark room, so that the beam of light falls upon it, it no longer has the
same direction, nor does it form a round spot, but an oblong painted image
of seven colors--red, orange, yellow, green, blue, indigo, and violet.
This is called the solar spectrum, and will be readily understood by
reference to the accompanying diagram, Fig. 1.

[Illustration: Fig. 1.]

To those who are unacquainted with the theory of light (and for their
benefit this chapter is given), it may be a matter of wonder how a beam of
light can be divided. This can be understood when I say, that white light
is a bundle of colored rays united together, and when so incorporated,
they are colorless; but in passing _through_ the prism the bond of union
is severed, and the colored rays come out _singly_ and _separately_,
because each ray has a certain amount of refracting (bending) power,
peculiar to itself. These rays always hold the same relation to each
other, as may be seen by comparing every spectrum or rainbow; there is
never any confusion or misplacement.

There are various other means of decomposing white light besides the
prism, of which one of the principal and most interesting to the
photographer, is by _reflection_ from colored bodies. If a beam of white
light falls upon a white surface, it is reflected without change; but if
it falls upon a _red_ surface, only the red ray is reflected: so also with
yellow and other colors; the ray which is reflected corresponds with the
color of the object. It is this reflected decomposed light which presents
the beautifully colored image we see upon the ground glass in our cameras.

[Sidenote: LIGHT, HEAT, AND ACTINISM.]

A sunbeam may be capable of three divisions--light, heat, and actinism;
the last causes all the chemical changes, and is the acting power upon
surfaces prepared to receive the photographic image. The accompanying
illustration, Fig. 2, will readily bring to the minds of the reader the
relation of these one to another, and their intensities in the different
parts of a decomposed sunbeam.

[Illustration: Fig. 2.]

The various points of the solar spectrum are represented in the order
in which they occur between A and B, this exhibits the limits of the
Newtonian spectrum, corresponding with Fig. 1. Sir John Herschel and
Seebeck have shown that there exists, beyond the violet, a faint violet
light, or rather a _lavender_, to _b_, which gradually becomes colorless;
similarly, red light exists beyond the assigned limits of the red ray
to _a_. The greatest amount of actinic power is shown at E opposite the
violet; hence this color "exerts" the greatest amount of influence in the
formation of the photographic image.

[Sidenote: COLORING WALLS BLUE.]

(Blue paper and blue color have been somewhat extensively used by our
operators in their operating rooms and skylights, in order to facilitate
the operation in the camera. I fancy, however, that this plan cannot
be productive of as much good as thought by some, from the fact, that
the light falling upon the subject, and then reflected into the camera,
is, coming through colorless glass, not affected by such rays as may be
reflected from the walls of the operating room; and even if it were so, I
conceive that it would be injurious, by destroying the harmony of Shadows
which might otherwise occur.) The greatest amount of white light is at C;
the yellow contains less of the chemical power than any Other portion of
the solar Spectrum. It has been found that the most intense heat is at the
_Extreme Red_, _b_.

Artificial lights differ in their color; the white light of turning
charcoal, which is the principal light from candles, oil and gas, contains
three fays--red, yellow and blue. The dazzling light emitted from lime
intensely heated, known as the _Drummond light_, gives the color of the
prism almost as bright as the solar spectrum.

[Sidenote: LIGHT, HEAT, AND CHEMICAL POWER.]

If we expose a prepared collodionized plate or sensitive paper to the
solar spectrum, it will be observed that the luminous power (the yellow)
occupies but a small space compared with the influence of heat and
chemical power. R. Hunt, in his _Researches on Light_, has presented the
following remarks upon the accompanying illustration:--

[Illustration: Fig. 3.]

"If the linear measure, or the diameter of a circle which shall include
the luminous rays, is 25, that of the calorific spectrum will be 42·10,
and of the chemical spectrum 55·10. Such a series of circles may well be
used to represent a beam from the sun, which may be regarded as an atom
of _Light_ surrounded with an invisible atmosphere of _Heat_, and another
still more extended, which possesses the remarkable property of producing
chemical and molecular change."

[Sidenote: REFRACTION.]

A ray of light, in passing obliquely through any medium of uniform
density, does not change its course; but if it should pass into a denser
body, it would turn from a straight line, pursue a less oblique direction,
and in a line nearer to a perpendicular to the surface of that body.
Water exerts a stronger refracting power than air; and if a ray of light
fall upon a body of this fluid its course is changed, as may be seen by
reference to Fig. 4. It is observed that it proceeds in a less oblique
direction (towards the dotted line), and, on passing on through, leaves
the liquid, proceeding in a line parallel to that which it entered. It
should be observed, that at the _surface_ of bodies the refractive power
is exerted, and that the light proceeds in a straight line until leaving
the body. The refraction is more or less, and in all cases in proportion
as the rays fall more or less obliquely on the refracting surface. It is
this law of optics which has given rise to the lenses in our camera tubes,
by which means we are enabled to secure a well-delineated representation
of any object we choose to picture.

[Illustration: Fig. 4.]

When a ray of light passes from one medium to another, and through that
into the first again, if the two refractions be equal, and in opposite
directions, no sensible effect will be produced.

[Sidenote: REFRACTION, LENSES, FOCUS.]

The reader may readily comprehend the phenomena of refraction, by means
of light passing through lenses of different curves, by reference to the
following diagrams:--

[Illustration: Fig. 5. Fig 6. Fig. 7.]

Fig. 5 representing a double-convex lens, Fig. 6 a double-concave,
and Fig. 7 a concavo-convex or meniscus. By these it is seen that a
double-convex lens tends to condense the rays of light to a focus, a
double-concave to scatter them, and a concavo-convex combines both powers.

[Sidenote: ENLARGING OR REDUCING IN COPYING.]

[Illustration: Fig. 8.]

[Illustration: Fig. 9.]

If parallel rays of light fall upon a double-convex lens, D D, Fig. 8,
they will be refracted (excepting such as pass directly through the
centre) to a point termed the principal focus. The lines A B C represent
parallel rays which pass through the lens D D, and meet at F; this point
being the principal focus, its distance from the lens is called the _focal
length_. Those rays of light which are traversing a _parallel_ course,
when they enter the lens are brought to a focus nearer the lens than
others. Hence the difficulty the operator sometimes experiences by not
being able to "obtain a focus," when he wishes to secure a picture of
some very distant objects; he does not get his _ground glass near enough
to the lenses_. Again, the rays from an object near by may be termed
diverging rays. This will be better comprehended by reference to Fig.
9, where it will be seen that the dotted lines, representing parallel
rays meet nearer the lenses than those from the point A. The closer the
object is to the lenses, the greater will be the divergence. This rule
is applicable to copying, Did we wish to copy a 1/6 size daguerreotype
on a 1/16 size plate, we would place it in such a position to the lenses
at A, that the focus would be at F, where the image would be represented
at about the proper size. Now, if we should wish to copy the 1/6 size
picture, and produce another of exactly the same dimensions, we have
only to bring it nearer to the lenses, so that the lens D E shall be
equi-distant from the picture and the focus, _i. e._ from A to B. The
reason of this is, that the distance of the picture from the lens, in
the last copy, is less than the other, and the divergence has increased,
throwing the focus further from the lens.

These remarks have been introduced here as being important for those who
may not understand the principles of enlarging or reducing pictures in
copying.

[Sidenote: LENSES.]

I would remark that the points F and A, in Fig. 9, are termed "conjugate
foci."

If we hold a double-convex lens opposite any object, we find that an
inverted image of that object will be formed on a paper held behind it. To
illustrate this more clearly, I will refer to the following wood-cut:--

[Illustration: Fig. 10.]

"If A B C is an object placed before a convex lens, L L, every point of it
will send forth rays in all directions; but, for the sake of simplicity,
suppose only three points to give out rays, one at the top, one at the
middle, and one at the bottom; the whole of the rays then that proceed
from the point A, and fall on the lens L L, will be refracted and form
an image somewhere on the line A G E, which is drawn direct through the
centre of the lens; consequently the focus E, produced by the convergence
of the rays proceeding from A, must form an image of A, only in a
different relative position; the middle point of C, being in a direct
line with the axis of the lens, will have its image formed on the axis
F, and the rays proceeding from the point B will form an image at D; so
that by imagining luminous objects to be made up of an infinite number
of radiating points, and the rays from each individual point, although
falling on the whole surface of the lens, to converge again and form a
focus or representation of that point from which the rays first emerged,
it will be very easy to comprehend how images are formed, and the cause of
those images being reversed.

"It must also be evident, that in the two triangles A G B and D G E, that
E D, the length of the image, must be to A B, the length of the object, as
G D, the distance of the image, is to G B, the distance of the object from
the lens."

[Sidenote: SPHERICAL ABERRATION.]

It will be observed, that in the last cut the image produced by the lens
is curved. Now, it would be impossible to produce a well-defined image
from the centre to the edge upon a _plain_ surface; the outer edges would
be misty, indistinct, or crayon-like. The centre of the image might be
represented clear and sharp on the ground glass, yet this would be far
from the case in regard to the outer portions. This is called _spherical
aberration_, and to it is due the want of distinctness which is frequently
noticed around the edges of pictures taken in the camera. To secure a
camera with a _flat, sharp field_, should be the object of every Operator;
and, in a measure, this constitutes the great difference in cameras
manufactured in this country.

Spherical aberration is overcome by proper care in the formation of the
lens:--"It can be shown upon mathematical data that a lens similar to that
given in the following diagram--one surface of which is a section of an
ellipse, and the other of a circle struck from the furthest of the two
foci of that ellipse--produces no aberration.

"At the earliest period of the employment of the camera obscura, a
_double-convex_ lens was used to produce the image; but this form was
soon abandoned, on account of the spherical aberration so caused. Lenses
for the photographic camera are now always ground of a concavo-convex
form, or meniscus, which corresponds more nearly to the accompanying
diagram."

[Illustration: Fig. 11.]

[Sidenote: CHROMATIC ABERRATION.]

_Chromatic Aberration_ is another difficulty that opticians have to
contend with in the manufacturing of lenses. It will be remembered, that
in a former page (14) a beam of light is decomposed by passing through
a glass prism giving seven distinct colors--_red_, _orange_, _yellow_,
_green_, _blue_, _indigo_ and _violet_.

Now, as has been said before, the dissimilar rays having an unequal degree
of refrangibility, it will be impossible to obtain a focus by the light
passing through a double-convex lens without its being fringed with color.
Its effect will be readily understood by reference to the accompanying cut.

[Illustration: Fig. 12.]

If L L be a double convex-lens, and R R R parallel rays of white light,
composed of the seven colored rays, each having a different _index_ of
refraction, they cannot be refracted to one and the same point; the red
rays, being the least refrangible, will be bent to _r_, and the violet
rays, being the most refrangible, to _v_: the distance _v r_ constitutes
the chromatic aberration, and the circle, of which the diameter is _a l_,
the place or point of mean refraction, and is called the circle of least
aberration. If the rays of the sun are refracted by means of a lens, and
the image received on a screen placed between C and _o_, so as to cut
the cone L _a l_ L, a luminous circle will be formed on the paper, only
surrounded by a red border, because it is produced by a section of the
cone L _a l_ L, of which the external rays L _a_ L _l_, are red; if the
screen be moved to the other side of _o_, the luminous circle will be
bordered with violet, because it will be a section of the cone M _a_ M
_l_, of which the exterior rays are violet. To avoid the influence of
spherical aberration, and to render the phenomena of coloration more
evident, let an opaque disc be placed over the central portion of the
lens, so as to allow the rays only to pass which are at the edge of the
glass; a violet image of the sun will then be seen at _v_, red at _r_,
and, finally, images of all the colors of the spectrum in the intermediate
space; consequently, the general image will not only be confused, but
clothed with prismatic colors.

To overcome the difficulty arising from the chromatic aberration, the
optician has only to employ a combination of lenses of opposite focal
length, and cut from glass possessing different refrangible powers, so
that the rays of light passing through the one are strongly refracted, and
in the other are bent asunder again, reproducing white light.

To the photographer one of the most important features, requiring his
particular attention, is, that he be provided with a good lens. By the
remarks given in the preceding pages, he will be enabled, in a measure, to
judge of some of the difficulties to which he is _occasionally_ subjected.
We have in this country but two or three individuals who are giving their
attention to the manufacture of lenses, and their construction is such,
that they are quite free from the _spherical_ or _chromatic aberration_.



CHAPTER II.

CAMERA--ARRANGEMENT OF LENSES--CAMERA TUBES--CAMERA-BOXES, BELLOWS, AND
COPYING--CAMERA STANDS--HEAD RESTS--CLEANING VICE--NITRATE BATH--LEVELING
STANDS--PRINTING FRAMES--COLLODION VIALS.


Babtista Porta, when he saw for the first time, on the walls of his dark
chamber, the images of external nature, pictured by a sunbeam which found
its way through only a small hole, little thought of the importance which
would be attached to the instrument he was, from this cause, led to
invent. The camera obscura of this Italian philosopher remained as a mere
scientific toy for years, and it was not until Daguerre's discovery that
its true value was estimated. It now plays a very important part in giving
employment to at least _ten thousand persons_ in this country alone.

It is of the utmost importance, in selecting a set of apparatus, to secure
a good camera; for without such no one can obtain fine pictures. In
testing it, see that it gives the pupil of the eye and lineaments of the
features sharp and distinct; and that the whole image on the ground glass
has a fine pearly hue. Look also to the field, and observe that the focus
is good at the centre and extreme edges of the ground glass, at the same
time. A poor camera generally gives a misty image, with the lights and
shades apparently running together. The best American cameras are fully
equal to those imported, while they cost much less; but there are great
numbers sold which are not worth using.

[Sidenote: CAMERA TUBES AND LENSES.]

If a lens gives a well defined image on the ground glass, it should do the
same on the plate. Many a valuable lens has been condemned for failing
in this, merely in consequence of the plate-holder not being in focus
with the ground-glass. In case of deficiency in this, put a glass into
the holder, lay a rule across the face, and measure the distance between
them very exactly; measure the ground-glass in the same way, and make
the distance agree perfectly, by moving the ground-glass either back or
forward in the frame, as the case may be, so that the surface of the
glass plate shall occupy precisely the same position as the face of the
ground-glass when in the camera.

[Illustration: Fig. 13. Fig. 14.]

[Sidenote: POSITION OF LENSES IN THE TUBE.]

It is very desirable that the operator should understand the arrangement
of the lenses in the tube; it not unfrequently happens, that in taking
out the "glasses" to clean them, he does not return them to their proper
places, and the result is that his "camera is spoiled." A couple of
illustrations and a few remarks will be sufficient to enable any one to
replace the lenses in them properly. Fig. 13 represents the tube for
holding the lens, and Fig. 14 shows their arrangement. It will be seen
that the two back lenses have a small space between them; this separation
is kept by a small tube or ring of the same circumference as the lens.
The two front lenses are nearest together. It will be observed that the
two thick lenses are towards each other; these are made of _flint glass_
containing much oxide of lead. The other two are double convex, and are
made of _crown glass_. By noting the fact that the two cemented lenses go
in the front of the tube, the glass having the thickest edge goes inside,
and that the _thickest lens_ of the other two goes in first, from the back
of the tube, it will not be easy for the operator to make a mistake in
returning the "glasses."

"I will remark that a diaphragm diminishes both chromatic and spherical
aberration, by cutting off the outside portion of the lens. It lessens
the brilliancy of the image, but improves the distinctness by preventing
various rays from interfering with and confusing each other; it also
causes a variety of objects at different distances to be in focus at the
same time."

[Illustration: Fig. 15.]

[Sidenote: CAMERA BOXES.]

The tube containing the lenses is to be mounted on a box (camera-box)
as in Fig. 15. For this purpose there are several patterns of boxes,
from among which I have made two selections of the most approved, and
represent them by cuts, Figs. 16, 17, 18.

[Illustration: Fig. 16.]

[Illustration: Fig. 17.]

Figs. 16 and 17 represent a bellows-box which is probably more in use than
all the other patterns together. They serve both for copying and taking
portraits from life. A is the base; B is the back and _sliding_-box;
C, bellows, which admits of extension or contraction; D is the opening
to receive the carriage A, Fig. 17; E is a thumb screw to hold the
sliding-box at any required distance. Fig. 17 represents the plate-holder
and ground glass frame.

A, carriage to pass through D, Fig. 16; B, frame for ground-glass, which
may be turned in a horizontal or perpendicular position; C, a movable
plate-holder held in place by means of springs; D, reducing holder, with
bottom and plate to hold the glass plate: any size of reducing frame can
be put in frame C; E E, spring bottom to keep frame D in place; F, slide;
G, thumb-screw, when the carriage is to be put in or taken out of the box,
Fig 16; H H, spring bottom to hold B in place.

Bellows-boxes can be obtained which receive the plate-holder from the
top, the same as in the copying-box, Figs. 15 and 18. The common wood, or
"copying-box," is represented by Fig. 18.

[Illustration: Fig 18.]

A, being the main or outside box, is made of wood veneered with rosewood;
B is another box which fits into A, sliding in and out as required. The
ground glass and plate-holders fit grooves made in the inside box.

In regard to plate-holders or tablets for holding the glass plates, it
need only be said that the camera-boxes are accompanied with a complete
set, so arranged that the light is wholly excluded from the plate while
drawing out or pushing in the slide, for shutting off the light while
the holder is out of the box. Should any one be desirous of using the
same camera, for taking both glass and daguerreotype pictures, it will be
necessary for him to be provided with two sets of tablets for his box, one
for each process.

[Illustration: Fig. 19.]


Camera Stands.

[Sidenote: CAMERA STANDS, ARM STANDS.]

There are several patterns of these; almost every dealer has some
particular style, which, if not for beauty, for his interest, suits
his purposes best. Among the assortment, I will present only two
illustrations. The first, Fig. 19, represents one which has an advantage
over many others; it is made of cast iron, and of an ornamental
pattern:--A, base on castors; B, fluted hollow column, which admits the
iron tube C, which has on one side a hollow tooth rack to receive a spiral
thread on the inner face of wheel D; this wheel, when turned, elevates or
lowers the tube C to any desired height; E, thumb wheel attached to a
screw which sets against tube C, to hold it in position, F, a pinion by
which the camera can be directed; G G, thumb screws to hold the two plates
together when in position. It is quite heavy, stands _firm_ and _solid_,
and is not liable to be moved by the jar from walking over the floor.
For permanently located operators these are the most desirable; but for
those who are moving about from place to place, and those who wish to take
views, a lighter article would be more convenient, such as one represented
at Fig. 20. This stand is made principally of wood, and can be readily
taken apart, so as to be packed in an ordinary sized trunk.

[Illustration: Fig. 20.]

[Illustration: Fig. 21.]

Fig. 21 represents a small "Jenny Lind Stand," and is a very convenient
article for the sitter to lean a hand or arm upon while sitting for a
portrait; It is fixed with a rod for raising or lowering the top, and can
be adjusted to any required height.


Head Rests.

[Sidenote: HEAD RESTS.]

There are several patterns of head supports, or, as they are commonly
called, head rests, in use by the profession. I give two illustrations
(Figs. 22 and 23). The first is an independent iron rest, known as the
"Jenny Lind Rest;" and the other is for fastening to the back of a
chair, as seen in the cut. For general use, I would recommend the iron
independent rest as far more advisable than any other.

[Illustration: Fig. 22.]

[Illustration: Fig. 23.]


Vices for Holding Glass.

[Sidenote: PLATE-HOLDERS, BATH, DIPPING RODS.]

The article used for holding the glass, during the process of cleaning,
is called a vice; and, of the numerous styles recently introduced, I find
none that I would prefer to the old one known in market as "Peck's Vice;"
it is simple and easy in operation, and at the same time is effectual.
Fig. 24 represents this vice, which is to be firmly secured to a bench;
the small piece of wood attached to the bottom is of no use. A A are the
grooved for receiving the daguerreotype plate-block; but as they are too
deep for the glass, I pin on a small strip of wood, so that the upper edge
of the glass will be a little above the projection of the vice.

[Illustration: Fig. 24.]

[Illustration: Fig. 25.]

[Illustration: Fig. 26.]

[Illustration: Fig. 27.]


Nitrate Baths and Dipping Rods.

The accompanying illustration, Fig. 25, _a_, represents a bath for holding
the nitrate of silver solution. This shape is of my own suggestion, and
the best adapted to the wants of the photographer. It will be seen that
the front side is rounding, with a curve extending from side to side. By
this shape, the _face_ of the glass is protected from coming in contact
with the side of the bath--both edges of it turning so as to prevent
injury. There is a small projection on the top, at the opposite side of
the oval; this is to allow the solution to flow over and wash off any dust
that may have gathered upon the surface of the solution. This wash runs
out of a small tube, as is shown in the cut. Any convenient vessel can be
placed under it to receive the liquid. This can be filtered and returned
as often as required. I am not in the practice of filling my baths full of
solution, but always keep them filtered and clean; hence saving an excess
of solution.

_b_ represents a little support, which is secured at its base Upon
the shelf, to hold the bath in a slightly inclined position, which is
preferable to having it stand perpendicularly.

[Illustration: Fig. 28.]

[Illustration: Fig. 29.]

[Illustration: Fig. 30.]


Leveling Stands.

[Sidenote: LEVELING STANDS.]

Persons oftentimes require a rest or place to put their glass during
development or washing the picture. Either of the stands represented by
the annexed cut will answer the purpose.

Fig. 30 is known to the daguerreotype operator as a "gilding stand," and
is the one best adapted to the wants of operators on glass. It may be
so arranged as to give the surface of the glass a water-level; D D are
thumb-screws, by means of which, when properly regulated, the frame G may
hold glass perfectly level and a large quantity of solution may be poured
over the surface.


Printing Frames.

[Sidenote: PRINTING FRAMES.]

There are numerous methods and apparatus used for holding the negative
and the paper during exposure to the light. The following illustrations
represent a convenient and economical frame for this purpose.

[Illustration: Fig. 31.]

[Illustration: Fig. 32.]

Fig. 31 represents the front of the frame. The negative glass is held upon
it by springs attached by screws to the bottom half of the frame, A, so
that they can be turned on or off, to suit the different sizes of glass.
On the other end of the spring are wooden buttons, which are placed on
the edges of the glass negative, holding it in its place, and pressing it
firmly against the paper which is placed under it. This frame is made of
two pieces of inch board, which are connected by hinges, falling over
as seen in Fig. 32, B being the half that is movable. This movable half
is secured in position by means of a wooden button, attached to A on the
back and under B, as seen in Fig. 32. The separate pieces, A and B, are
bevelled where they connect, as seen by Fig. 31. D (in Fig. 32) is one of
the springs, which can be seen in Fig. 31.

The entire bed or face of the frame, A and B, should be covered with a
thick piece of satinet cloth, which may be pasted to the lower half, A,
and extended over the entire surface of A and B. This forms a pad for the
paper.

This printing frame can be easily made by any cabinet-maker or carpenter.
The springs may be of sheet iron or brass--either will be found
sufficiently stiff for the purpose. Every operator should be provided with
from four to ten frames: the saving of time will be found to amply repay
the expenditure necessary for a good supply.

[Illustration: Fig. 33.]

Another article called a pressure frame, is represented in the
accompanying figure. This is more expensive than the first, and is by some
considered preferable.

Another cheap, convenient and equally good arrangement for holding the
negative and paper, is to take three glasses--say one a full size, being
the one having the negative upon it; and then take two glasses, each just
half the size of the negative, and have a piece of _very thick heavy_
cloth cut the size of the negative glass, which can be put between it and
the two half glasses, and then they can be held together by means of the
common spring clothes pin. The advantage of the two glasses at the back
is, that one can be entirely removed while the picture is being examined,
and afterwards returned without, in the least, moving the impression.


Collodion Vial.--Color-Boxes.

[Sidenote: COLLODION VIALS. COLOR-BOXES.]

This shaped vial is made expressly for collodion, to which purpose it
is admirably adapted. It has a wide mouth, and is so constructed that
the liquid flows clear and free. It is deep, and with a heavy protruding
base, to prevent its falling. There are two sizes made at present, one to
contain 2-1/2 ounces--the other, 1-1/2 ounce. I generally use the smaller
ones, but always keep on hand, and would not be without, a few of the
larger size.

[Illustration: Fig. 34.]

[Illustration: Fig. 35.]

Fig. 35 represents a color-box. These can be had of any dealer, completely
fitted, with color and brushes for use.



                               =CHEMISTRY.=

                                ~~~~~~~~~~

                             PRACTICAL HINTS
                                    ON
                        =PHOTOGRAPHIC CHEMISTRY.=



CHAPTER III.

SOLUBLE COTTON--MANIPULATION--PLAIN COLLODION--BROMO-IODIZED COLLODION
FOR POSITIVES--DITTO FOR NEGATIVES--SOLUTION OF BROMIDE AND IODIDE OF
POTASSIUM AND SILVER--DOUBLE IODIDE OF POTASSIUM AND SILVER--DEVELOPING
SOLUTION--FIXING THE SOLUTION--BRIGHTENING AND FINISHING THE
IMAGE--PHOTOGRAPHIC CHEMICALS.


The chemistry of Photography requires the attention, in a greater or less
degree, of every practitioner. It is of the utmost importance, that those
who wish to meet with success in the various processes given, should not
only be provided with a good selection of chemicals, but also understand
the nature of the agent employed. To give a perfectly complete and full
list of every agent used would require more time and space than can be
given in this work. I shall confine myself to some of the most important,
and to such articles as are of the greatest interest to the practitioner.


Soluble Cotton.

I have, in my practice and trade, adopted the term _soluble cotton_ as the
one most appropriate, making a desirable distinction from the article sold
as _gun cotton_, they being of a somewhat different nature--gun cotton
being the most explosive and least soluble, while the other preparation is
more soluble and less explosive.

There are two methods employed in the preparation of soluble cotton;
one being by the use of nitric and sulphuric acids, and the other with
sulphuric acid and nitrate of potash. The last of these I would recommend
as being the most convenient for those who require only a small quantity
of cotton. Persons experimenting in the preparation of this article
should exercise much care and judgment. A good cotton is not the result
of hap-hazard operation. The operator should be acquainted, as nearly as
possible, with the quality of the chemicals employed, and the proper mode
of manipulation.

_Articles necessary._--One quart Wedgewood mortar and pestle, or
evaporating dish; one glass rod; one pane of glass, large enough to cover
the mortar or dish; one ordinary-sized pail two-thirds full of pure rain
or distilled water, and at least ten times that quantity of water at hand;
twelve ounces (by weight, avoirdupois) of nitrate of potash (Dupont's
refined, pulverized); twelve ounces (by measure) of commercial sulphuric
acid; and three hundred and forty grains of clean, pure cotton wool.

_Remarks._--It is advisable that the mortar or dish be deep and narrow,
as the mixture can be better formed in a vessel of this shape. If not
convenient to procure a mortar, a common earthen bowl will answer; glass
is objectionable, as the heat generated in the combination of the acid and
nitre is liable to crack it. A new pail should not be used, especially
if it is painted, as the acids attack the paint, and injure the cotton.
I prefer one that has been used for some time, and has been frequently
cleaned. A common earthen wash-bowl, or any large glass dish, will answer
in place of the pail. Metal pails or vessels should not be used.

_Nitrate of Potash_ (saltpetre) should be dry and finely-powdered. I use
none other than Dupont's refined; this is very nearly, if not absolutely,
chemically pure.

The commercial _Sulphuric Acid_ (oil of vitriol) of America is of great
uniformity of strength, as sold by druggists generally. I use a test-bulb
graduated to the proper density, and have been very successful in my
experiments.

In some twenty different samples of acid, used in different cities in the
United States, I found only one that produced a poor cotton, and this
might have been influenced by the moisture of the atmosphere, it being a
very rainy day when I used it.

During my recent and somewhat extensive practice, I have thought that
the _fine long fibres_ of cotton wool do not make so desirable a soluble
cotton as that which is heavy or common. Four or five very careful
experiments upon this point, have had the effect to produce in me a strong
belief that my ideas are entitled to some consideration. I should not
select the _finest_ cotton for making soluble cotton, but now invariably
take that which is _thick_ or _coarse_.

The result of my experience is (other things being equal), that cotton
prepared in fine dry weather has a greater degree of solubility than when
prepared in a moist atmosphere: hence I would recommend the experimenter
to choose fine, clear weather for preparing it.


=Manipulation.=

Having at hand every article requisite, proceed as follows:--Put the
nitrate of potash into the mortar or dish; be sure it is dry and well
powdered, and then add the acid; stir them well with the pestle and glass
rod, so that the lumps will be all (or nearly so) out, and a pasty
solution formed. This operation should not occupy more than two minutes'
time. Then put in the cotton, about one-quarter of the whole bulk at a
time: it should be well picked apart, so that it may come immediately in
contact with the acids, and should be _kneaded_, with the pestle and glass
rod, into the solution, and as soon as wetted, another quarter should be
added and wetted as soon as possible; so continue until all is in: then
_knead_ with the pestle and mortar for at least four minutes, or until
every fibre of the cotton is _saturated_ with the liquid; then the mortar
should be covered over with the pane of glass, and allowed to stand for
fifteen or twenty minutes; then the entire contents of the mortar should
be thrown into the pail two-thirds full of water, and stirred with the
glass rod as rapidly as possible: if this rapid stirring is omitted, the
cotton will be injured by the action of the acids in combining with the
water. The water should be poured off, and another change put into the
pail.

After about three changes, the hands may be used in the farther washing.
The hands should be perfectly clean, and free from _all chemicals_. The
changes of water and washing should be continued until every trace of acid
has disappeared, which can be seen by testing with blue litmus test-paper.
After it is thought that the cotton has become free, the water may be
squeezed out of a little lump about the size of a pea, and then placed
between the fold of the test-paper, and if it reddens the paper, there is
acid present, and the washing should be continued until there is no change
in the paper. When this is done, the cotton can be put into the folds of
a dry towel or cloth (which has been thoroughly rinsed, so that no soap
be present), and wrung out as dry as possible, and then it may be picked
apart and put aside, exposed to a moderate temperature (say 100° Fahr.) to
dry, when it is ready for use.

I employ the method (for convenience, nothing more) of displacing the
water by the use of alcohol. [_Cutting's patent--see patents._] I wring
out the water as before, then place the cotton in strong alcohol, stir
and press it, and then pour it off; wring it out again, then put it in a
change of alcohol, let it soak for about five minutes, then wring it out
as dry as possible, pick it apart, and it will dry immediately, and place
it in a close stoppered bottle; or, if wanted for use at once, put it into
the dissolving solution immediately.

I will here remark that, since the first edition, I have had occasion
to use large quantities of soluble cotton, and have found that if it be
kept in an atmosphere of alcohol and ether, its solubility is somewhat
improved: that is, in the case of its not being used immediately after
its preparation. This is easily kept, by dropping a few drops of ether or
alcohol into the bottle containing it, and then sealing close until wanted
for use. In the event of the water being displaced by alcohol, it is not
necessary to thoroughly dry it, but put in a _perfectly close_ bottle to
keep.

_Remarks._--There are a few precautions necessary to be observed in the
preparation of soluble cotton. I should select a fine clear day, if time
is no object; nevertheless I have made a good article in a moderately
dense atmosphere. Sulphuric acid has a powerful affinity for hydrogen,
consequently, in damp weather, it is more or less reduced by the moisture
in the air.

It is advisable to prepare the nitro-sulphuric acid mixture on a roof,
or between two doors or windows, where there is a good current of air,
in order to prevent the inhalation of white vapors which arise, and are
very poisonous to the lungs. As a preventive, in case of inhaling these
vapors, I apply the fumes of aqua-ammonia. It is best for every one to
have six or eight ounces of this always at hand; it neutralizes all acid
that maybe spattered on the clothes, prevents its destructive powers, and
restores the color.

Yellow vapors sometimes appear when putting the cotton in contact with the
solution: this arises from its not being wet; and when they do appear, the
cotton where they are should be quickly put under the liquid and kneaded
rapidly, which will prevent a continuance of these vapors. I have had them
appear, and used the cotton, and could not observe that any bad effect had
been produced.

The temperature is worthy the attention of the operator: if it be low,
as in winter, and the cotton be left in the nitro-sulphuric mixture for
fifteen or twenty minutes, the whole becomes a thick, stiff mass, bedded
together, and has not had proper action, giving a bad article. A good
temperature is about 140° Fahr. for the last of the time the cotton is
in the mixture. This is not always convenient; so the operator will be
governed by circumstances, taking his chance of having a good article. In
some cases I have heated a _thick_ iron plate, at a moderate temperature,
placing the mortar upon it, and thus aided in regulating the temperature.
This is the most convenient method I have employed.

It has been thought advisable to publish in full the account of Edw.
Ash Hadow's experiments and investigations upon the subject of soluble
cotton. The following is an account of them as it appeared in _Humphrey's
Journal_, vol. VI. p. 12:--

"Having, in my earlier experiments on the collodion process of
photography, experienced some difficulty in always producing a collodion
of uniform quality with regard to sensitiveness, tenacity and fluidity,
although making use of the same materials for its preparation, and this
I find being the complaint of many others, it has been my study lately
to determine the variations in quality to which the ingredients are
liable, and the effects of these variations on the sensitive film, and
likewise to ascertain whether the excellent qualities of some samples of
collodion depend on the materials in ordinary use, or on some substances
accidentally or intentionally added. Researches in the preparation of
collodion may appear superfluous, now that it is supplied of the best
quality by so many makers; but as some persons of an independent turn of
mind still prefer manufacturing their own, I venture to bring forward
the subject with the hope of benefiting them. In this beautiful process
so much depends for success on the quality of the collodion, that when
in possession of a good specimen, it becomes one of the easiest and most
simple, and ought to be the most certain of all the processes yet devised;
for here no material of uncertain composition is introduced, such as
paper, and thus we have nothing to fear from plaster of Paris, alumina,
or specks of iron or copper, which continually endanger or modify the
calotype process; each ingredient can and ought to be obtained in a state
of perfect purity, and with this precaution the degree of success depends
upon the skill of the operator himself.

"Of all the substances used in this process, the gun-cotton is usually
the only one actually prepared by the operator himself; in this he cannot
fail to have observed the great variations in the solubility, and, when
dissolved, the transparency and tenacity of the films, to which it
is liable; the various processes also that are given appear at first
sight unaccountably different, some directing ten minutes, others a few
seconds immersion. In consequence of this I have specially examined into
the cause of all these variations, with a view to obtain certainty, and
also have endeavored to discover how far they affect the sensitiveness
of the prepared surface. If we take a mixture of the strongest nitric
and sulphuric acids and immerse as much cotton as can be wetted, after
some minutes squeeze out the acid as far as possible, then immerse a
second portion of cotton, and again express the acids for a third portion
of cotton, and so on until the liquid is exhausted, we shall find, on
comparing the cottons thus treated, after washing and drying, that there
is a gradual alteration in their properties, the first being highly and
perfectly explosive, and each succeeding portion less so, until the
portion last immersed will be found hardly explosive, leaving distinct
traces of charcoal or soot when burned. This may not appear surprising at
first sight, as it may be imagined that the latter portions are only a
mixture of gun-cotton and common cotton; this is, however, not the case,
for if each quantity be immersed sufficiently long, it will not contain
a fibre of common cotton, and may yet become charred on burning like
unaltered cotton. The most remarkable difference, however, is discovered
on treating them with ether containing a little alcohol, when, contrary
to what might have been anticipated, the first or strongest gun-cotton
remains untouched, while the latter portions dissolve with the utmost
ease, without leaving a trace behind, which alone is sufficient proof that
no unaltered cotton remains. This difference in properties is owing to the
gradual weakening of the acid mixture, in consequence of the nitric acid
being removed by the cotton, with which it becomes intimately combined, at
the same time that the latter gives out a proportionate quantity of water.
In consequence of these experiments, a great many mixtures of these acids
were prepared of various strengths, each being accurately known, both to
determine whether there were more than one kind of _soluble_ gun-cotton,
and, if there were, to ascertain exactly the mixture required to produce
the most suitable to photographic purposes. By this means, and by, what
I believe has not been pointed out, _varying the temperature_, at least
five varieties were obtained;--first, gun-cotton, properly so called, as
before stated, quite insoluble in any mixture of alcohol and sulphuric
ether. Secondly, an explosive cotton, likewise insoluble, but differing
chemically from the first, obtained by a mixture of certain strength
when used _cold_. If _warm_, however, either from the heat produced
spontaneously on mixing the two acids; or by raising the temperature
artificially to about 130°, the cotton then immersed becomes perfectly
soluble, producing a third variety; if, however, it be _thoroughly dried_,
it becomes in a great measure insoluble. The fourth is obtained by the
use of weaker acids used cold, and the fifth when the mixture has been
warmed to 130° previous to the immersion of the cotton; in either of the
two last cases the product is perfectly soluble, but there is a remarkable
difference between their properties, for on dissolving 6 grains of each in
1 ounce of ether, the cotton treated with _warm_ acids gives a perfectly
fluid solution (which is likewise the case with the third variety produced
by acids something stronger), while that obtained by the use of cold acids
makes a mixture as thick as castor-oil.

"Having obtained these more strongly marked varieties, as well as
intermediate kinds, with all gradations of solubility, it was necessary,
before I could select any particular formula for preparing the cotton,
to compare their photographic properties, with especial reference to
sensitiveness, opacity of the reduced silver in negatives, and its color
in positives. A certain weight of each being dissolved in a portion of
the same mixture of alcohol and ether previously iodized, the comparison
was made, by taking the same objects with each collodion in succession,
and likewise by pouring two samples on the same plate of glass, and thus
exposing them in the camera together, side by side; this last proved
to be much the most satisfactory plan, and was repeated many times for
each sample, taking care to reverse the order in which they were poured
on, that there might be no mistake arising from the difference of time
elapsing between the pouring on of the collodion and its immersion in
the sensitive bath. By these experiments I had confidentially hoped to
have solved the question as to the cause of difference in sensitiveness
and other photographic properties of collodion; but in this I was
disappointed, for, after repeated experiments, I believe I may safely
affirm that they are precisely similar as regards their photographic
properties. The same I believe may be said of Swedish paper collodion,
judging from a few comparative experiments I have made, and indeed it is
difficult to discover what is the superiority of this material over clean
cotton-wool; the ease of manipulation which some allege is a matter of
taste, but I should decidedly prefer the open texture of cotton to that of
a substance like filtering paper, composed of a mass of compacted fibres,
the innermost of which are only reached when the acids have undergone
a certain degree of weakening by the water abstracted from the outer
fibres; and when we consider that from cotton alone we have the means of
preparing all varieties of collodion, from the most powerfully contracting
and transparent to the weakest and most opaque, and each if required with
equal and perfect certainty, there appears to be choice enough without
resorting to another material, differing only in being more rare and
more difficult to procure. But, although the photographic properties of
these varieties of collodion-wool are so similar, other circumstances,
such as fluidity, tenacity, and transparency, render its preparation of
some importance, and indicate that the acid mixture should always be used
warm; and it is chiefly in consequence of this very circumstance, that
greater success attends the use of nitrate of potash and sulphuric acid
than that of mixed acids; for the former when mixed, produce the required
temperature, and must be used while warm, since on cooling the mixture
becomes solid, whereas acids when mixed do not usually produce so high
a temperature, and being fluid can be used at any subsequent period;
another obstacle to their use is the great uncertainty of the strength of
the nitric acid found in the shops, requiring a variation in the amount
of sulphuric acid to be added, which would have to be determined by
calculation or many troublesome trials. When a proper mixture is obtained,
the time of immersion is of no importance, provided it be not too short,
and the temperature be maintained at about 120° or 130°; ten minutes is
generally sufficient; (though ten hours would not render the cotton less
soluble, as is sometimes asserted.)

"In using the mixed acids, the limits are the nitric acid being too
strong, in which case the product is insoluble, or too weak, when the
cotton becomes immediately matted or even dissolved, if the mixture
is warm. I have availed myself of these facts in order to produce
collodion-wool by the use of acids, without the trouble of calculating
the proper mixture according to their strength. Five parts by measure of
sulphuric acid, and four of nitric acid of specific gravity not lower
than 1·4, are mixed in an earthenware or thin glass vessel capable of
standing heat; small portions of water are added gradually (by half
drachms at a time, supposing two ounces to have been mixed,) testing after
each addition by immersion of a small portion of cotton; the addition of
water is continued until a fresh piece of cotton is found to contract and
dissolve on immersing; when this takes place, add half the quantity of
sulphuric acid previously used, and (if the temperature does not exceed
130°, in which case it must be allowed to cool to that point,) immerse
as much cotton, well pulled out, as can be easily and perfectly soaked;
it is to be left in for ten minutes, taking care that the mixture does
not become cold, and then transferred to cold water, and thoroughly
washed; this is a matter of much importance, and should be performed at
first by changing the water many times, until it ceases to taste acid,
and then treating it with boiling rain-water until the color of blue
litmus remains unchanged; the freedom from all trace of acid is insured
by adding a little ammonia before the last washing. Cotton thus prepared
should dissolve perfectly and instantaneously in ether containing a little
alcohol, without leaving a fibre behind, and the film it produces be of
the greatest strength and transparency, being what M. Gaudin terms 'rich
in gun-cotton.'

"The mixture of nitrate of potash and sulphuric acid is defective chiefly
from the want of fluidity, in consequence of which the cotton is less
perfectly acted on; this may be remedied by increasing the amount of
sulphuric acid, at the same time adding a little water; a mixture of 5
parts of dried nitre, with 10 of sulphuric acid, by weight, together
with 1 of water, produces a much better collodion wool than the ordinary
mixture of 1 of nitre with 1-1/2 of sulphuric acid. The nitre is _dried_
before weighing, in order that its amount, as well as that of the water
contained in the mixture, may be definite in quantity; it is then finely
powdered, mixed with the water, and the sulphuric acid added; the cotton
is immersed while the mixture is hot, and afterwards washed with greater
care even than is required when pure acids are used, on account of the
difficulty of getting rid of all the bisulphate of potash that adheres to
the fibres, which both acts as an acid and likewise causes the collodion
to appear opalescent when held up to the light; whereas the solution
should be perfectly transparent."


Plain Collodion.

[Sidenote: PLAIN COLLODION.]

To dissolve the soluble cotton (pyroxyline), and form plain collodion,
proceed as follows:

Take of

  Sulphuric ether (concentrated),                    10 ounces
  Alcohol, from 90 to 95 per cent.,                   6    "

Soluble cotton enough to give the solution a consistency such as will
allow it to flow evenly over the surface of the glass, and impart to
it quite a thick and transparent coating. If the coating is opaque, the
cotton has not been properly prepared, the acid mixture has been too weak.

_Remarks._--It is desirable for every operator to use chemicals of uniform
strength, and the better method to adopt is to employ those purchased
from some one respectable manufactory, and not take those furnished by
irresponsible and unconscientious parties. At least one-half of the
failures experienced by beginners is from want of good chemicals. It is
not economy to purchase a _cheap article_.

_Alcohol_ is an article that can be procured in almost any small village
in the United States, and is in general fit for collodion purposes. I
have used 88 per cent, in the above proportions, also the intermediate
varieties to 98 per cent., and have been quite successful; but feel
convinced that the ordinary 98, as marked (which usually stands by actual
test 95 to 97 per cent.), is preferable, except in cases where water is
employed in dissolving the iodizing salts, when I would use fully 98 per
cent.

Before concluding the subject on plain collodion, I will introduce
the account given by Mr. E. A. Hadow of his interesting and valuable
experiments, as published in _Humphrey's Journal_, Vol. VI, page 18.

"Having obtained good collodion-wool, the next point of inquiry was with
regard to the solvent; to ascertain whether the addition of alcohol
beyond what is necessary to cause the solution of the gun-cotton in
ether, were beneficial or otherwise. For this purpose ether and alcohol
were prepared perfectly pure, and mixtures were made of 1 of alcohol
to 7 of ether, 2 to 6, 3 to 5, 4 to 4 and 5 to 3. In one ounce of each
were dissolved 6 grains of gun-cotton and 4 grains of iodide of ammonium
(iodide of potassium could not be employed, since it requires a certain
amount both of water and alcohol to keep it in solution); they were then
compared, using a 35-grain solution of nitrate of silver, both by pouring
on separate glasses, and likewise by covering two halves of a plate with
two samples, as in examining the gun cottons, thus placing them under the
same circumstances during the same time; in this way the effect of adding
alcohol was very clearly perceived, since the difference between the
collodions was much greater than could have been anticipated.

"The first mixture containing only 1/8th of alcohol was quite unfit for
photographic purposes, from its being almost impossible, even with the
most rapid immersion, to obtain a film of uniform sensitiveness and
opacity throughout, the surface generally exhibiting nearly transparent
bands, having an iridescent appearance by reflected light.

"The second mixture with 1/4th of the alcohol is liable to great
uncertainty, for if there be any delay in pouring off the collodion the
same appearances are seen as in the first, and like it the surface is very
insensitive to light, while if the plate be rapidly plunged in the bath,
the collodion film becomes much more opaque than before, and is then very
sensitive.

"The third proportion of 3 of alcohol to 5 of ether is decidedly the best,
giving without the least difficulty a beautifully uniform and highly
sensitive film, at the same time perfectly tough and easily removable
from the glass if required. A further addition of alcohol, as in the
two last collodions, was not attended with any corresponding advantage
or increase of sensitiveness; on the contrary, the large proportion of
alcohol rendered them less fluid, though with a smaller quantity of gun
cotton they would produce very good collodions, capable of giving fine
films: the cause of the weakness of the film, observed on adding much of
the ordinary alcohol, is the large amount of water it usually contains.

"This surprising improvement, caused by the addition of a certain quantity
of alcohol, is referable to causes partly chemical, partly mechanical,
for, on examining the films, it will be found in the first, and
occasionally in the second collodion, that the iodide of silver is formed
on the surface, and can be removed entirely by friction without destroying
the transparent collodion film below, while in those collodions that
contain more than one-fourth of alcohol, the iodide of silver is wholly in
the substance, and in this state possesses the utmost sensitiveness.

"This difference of condition is owing to the very sparing solubility
of ether in water, which in the first case prevents the entrance of the
nitrate of silver into the film, consequently the iodide and silver
solutions meet on the surface; but on addition of alcohol, its solubility
enables the two to interchange places, and thus the iodide of silver is
precipitated throughout the substance in a state of the utmost division.
This difference is clearly seen under the microscope, the precipitate
being clotted in the one case, while in the other the particles are hardly
discoverable from their fineness.

"The presence of a little water considerably modifies these results, since
it in some degree supplies the place of alcohol, and is so far useful;
but in other respects it is injurious, for, accumulating in quantity,
if the collodion is often used, it makes the film weak and gelatinous,
and what is worse, full of minute cracks on drying, which is never the
case when pure ether and alcohol are used. Since the ether of the shops
almost always contains alcohol, and frequently water, it is important
to ascertain their amount before employing it for the preparation of
collodion; the quantity of alcohol may be easily ascertained by agitating
the ether in a graduated measure glass (a minim glass does very well)
with half its bulk of a _saturated_ solution of chloride of calcium; this
should be poured in first, its height noted, and the ether then poured
on its surface, the thumb then placed on the top, and the two agitated
together; when separated, the increase of bulk acquired by the chloride of
calcium indicates the quantity of alcohol present, and for this allowance
should be made, in the addition of alcohol afterwards to the collodion.

"Water is readily detected, either in ether or alcohol by allowing a
drop to fall into spirits of turpentine, with which they ought to mix
without turbidity; this is immediately produced if they contain water:
for detecting water in _alcohol_, benzole is a more delicate re-agent
than spirits of turpentine (Chemist, xxix, 203). It is also necessary
that ether should be free from a remarkable property it acquires by long
keeping, of decomposing iodides and setting free iodine, which thus
gives the collodion a brown color; the same property may be developed in
any ether, as Schonbein discovered by introducing a red hot wire into
the vapor in the upper portion of a bottle containing a little ether
and water; if it be then shaken up and a solution of iodide poured in,
the whole rapidly becomes brown; this reaction is very remarkable and
difficult to explain for even a mixture of the ether and nitric acid fails
to produce a color _immediately_. Ether thus affected can only be deprived
of this property by rectification with caustic potash."


Bromo-Iodized Collodion for Positives.--No. 1.

[Sidenote: IODIZED COLLODION FOR POSITIVES.]

One very important object in connection with this part of the collodion
process is to have chemicals of a good quality, and always employ those of
a fixed standard.

  Plain collodion,                                   10 ounces.
  Solution of bromide, and iodide of potassium and
    silver, (page 61)                                 3 drachms.
  Iodide of ammonium,                                10 grains.
  Hydro-bromic acid                                   6 drops.

Double iodide of potassium and silver (see page 62) enough so that when
the plate comes from the nitrate of silver bath, it will have an opaque
cream color.

_Remarks._--In the preparation of this sensitive collodion, it is
necessary to be cautious and not add too much of the iodide of potassium
and silver, for in that case the coating would flake off, and falling into
the silvering solution, the operator would be obliged to filter it before
he could silver his plate with safety as regards spotting it.

The method I employ is to add the plain collodion, bromide and iodide of
potassium and silver, iodide of ammonium and hydro-bromic acid, and then
cautiously add the double iodide of potassium and silver from five to
ten drops at a time, trying the collodion from time to time by pouring
a little on a narrow strip of glass, which I dip into the silvering
solution, and let it remain for two minutes. If the coating assumes the
proper color (a cream color), I shake the contents of the bottle, and then
stand it aside to settle: it is better after it has stood for a week or
two.

This collodion I have used after it has been made eight months, and
produced fine and satisfactory results, and use this nearly altogether
in practice. Since the first edition of this work has been issued, I have
sold over two thousand pounds of this preparation, and the demand is on
the increase. I will append another preparation (No. 2) which I have
successfully employed, and some operators prefer.


Bromo-Iodized Collodion for Positives.--No. 2.

  Plain collodion                                    10 ounces.
  Iodide of potassium                                30 grains.
  Bromide of ammonium                                20    "

Enough of the double iodide of potassium and silver to give the coating a
cream color when it comes from the silvering solution. It will take from
one to three drachms. Or this last may be omitted, and a few drops of a
saturated solution of dry iodine in alcohol may be added. Either of these
plans have been successful in my practice.

_Remarks._--The iodide of potassium being insoluble in the collodion, it
should be first dissolved in as little water as possible; _i. e._, take
the quantity, 30 grains, put it into a one-ounce graduate, and with a
glass rod stir it, adding water, drop by drop, only until all of the salt
is dissolved. Then it may be poured into the collodion, and there will be
a white powdery precipitate.

The bromide of ammonium will dissolve in the collodion, and can be put
into it. When all of the accelerators are in, it should be well shaken,
and then allowed to settle and become clear. When wanted, a sufficient
quantity may be poured into a vial (see Fig. 34) for use, and the main or
stock bottle should not be disturbed oftener than necessary. This last
collodion is not as durable as the first, but is less trouble to prepare.


Bromo-Iodized Collodion for Negatives.

[Sidenote: IODIZED COLLODION FOR NEGATIVES]

  Plain collodion                                     8 ounces.
  Iodide of potassium (dissolved as per page 62)     24 grains.
  Bromide of ammonium                                16   "

This collodion should be allowed to stand and settle twenty-four hours
before it is used: when wanted, it should be poured off into a collodion
vial. The more free the collodion is from sediment and small particles
of dust or undissolved cotton, the softer and more perfect will be the
impression it makes.

In case the above proportions of iodide of potassium should not produce a
cream-colored coating, when it comes from the nitrate of silver bath, more
may be added: for example, if the coating is of a bluish tint, I would
dissolve 6 grains of iodide of potassium in water, as before, and then try
it: shake well, and test it by putting a little on a slip of glass, and
dipping it into the silvering solution; if it coats to a cream-color, it
is right.

It should be borne in mind, that after the addition of iodide of potassium
here recommended, the collodion should be allowed to stand until settled,
before undertaking to produce a picture, although the coating may be
previously tested by means of a slip of glass.


Solution of Bromide and Iodide of Potassium and Silver.

Dissolve 130 grains of crystallized nitrate, of silver in 4 ounces of
pure water, in a long 8-ounce vial. Then in a clean 1-ounce graduate, or
some other convenient vessel containing half an ounce of water, dissolve
130 grains bromide of potassium. When this and the nitrate of silver are
both dissolved, pour the solution of bromide of potassium into the vial
containing the silver, and a thick yellow precipitate will fall. This
is the bromide of potassium and silver. This should be washed by nearly
filling the vial with water; shake it, and then let it settle, which it
will readily do, and then pour on the water, leaving the yellow mass in
the bottom of the vial; continue this operation of washing for at least
ten changes of water; then, after draining off the water as close as
possible, put into the vial four ounces of alcohol, shake it well and let
it settle; then pour off as close as possible. By this means the water is
nearly all taken out.

Pour into the vial _three_ ounces of alcohol; then in a small mortar
finely pulverize one ounce of iodide of potassium, and the solution, which
was before clear, will be more or less of a yellow color, and the bulk of
the yellow precipitate will be diminished. I have sometimes completely
re-dissolved the yellow precipitate, but this does not often occur, except
there be more water present than is advisable. It is better to have an
excess of bromide of potassium in the solution. This can be seen by its
being white, and remaining undissolved in the bottom of the vial. This
solution should be prepared in the evening, or in a dark room, and only
the light of a lamp or candle employed.


Double Iodide of Potassium and Silver.

This solution is made in the same manner as in the foregoing article,
substituting the iodide of potassium for the bromide--no bromide being
used in this preparation. The yellow precipitate in this case will be
re-dissolved and taken up in the solution: it may require more than one
ounce of pulverized iodide of potassium to effect this, but it may be
added in excess, so that the solution shall contain a quantity in powder.


Developing Solution.

[Sidenote: DEVELOPING SOLUTION.]

  Protosulphate of iron,                              3 ounces.
  Rain or distilled water,                            1 quart.

Put these into a quart bottle, and shake until the crystals are all
dissolved, and this can be kept for a stock bottle, and when wanted for
use pour into another bottle.

  Of the above solution,                              5 ounces.
  Acetic acid (No. 8)                                 1   "
  Chemically pure nitric acid                        20 drops.

Shake this mixture well, and filter through a sponge, and it is ready for
use. I file a mark in this bottle indicating five ounces, and another for
1 ounce: this will save time in mixing the solution.

_Remarks._--In my recent tour of the United States, I found it difficult
to obtain a good article of protosulphate of iron, and in its stead I
used the common copperas, such as I could find almost in any store. I
employ from one-fourth to one-half more than the quantity given above. If
it looked a clear green, and free from a white or brownish powder, about
one-fourth addition: _i. e._, four ounces, instead of three, as given
above. If the solution in the stock bottle is not wanted for a week or
more, a few crystals of the protosulphate of iron should be added, as it
decomposes, and the strength is depreciated.

There is quite a difference in the strength of the acetic acid as sold by
out country druggists, and the operator should be sure that he has No. 8,
to which quality the above proportions are adapted. I never have employed
the developing solution but once, but can see no objections to use it for
a number of glass plates, but it should be filtered every time before
using. The quantity of nitric acid may be increased, so long as a proper
proportion is preserved with the strength of the bath. The effect of this
addition of acid will be to brighten the impression; but if carried too
far, the reduction (developing) will be irregular, and the harmony of the
impression injured.


Fixing Solution.

[Sidenote: FIXING SOLUTION.]

  Water,                                              8 ounces.
  Cyanide of potassium,                         about 1 drachms

_Remarks._--I put enough of the cyanide of potassium into the water to
make the solution of such strength as to dissolve off the iodide of
silver ("coating") in from twenty to sixty seconds. The operation is
quite similar to that of hyposulphate of soda upon the coating of the
Daguerreotype plate. A too concentrated solution is likely to injure the
sharpness of the image.


Brightening and Finishing the Image.

[Sidenote: HUMPHREY'S COLLODION GILDING.]

The article I now employ for finishing off my Positives is in market,
and known as Humphrey's Collodion Gilding. It is a new preparation, and
exerts a powerful influence upon the image, having the same brightening
effect as chloride of gold on the daguerreotype. There is no article now
in market that equals this. I have until quite recently used a varnish
for this purpose, but having something that is of far greater value, I
have discarded it. It is one of the most valuable improvements since the
application of the Collodion Film as a vehicle for producing photographic
images. It is a new discovery, and is being rapidly brought into use by
the first ambrotypers and photographers in America. It adds at least
one-half to the beauty of an ambrotype, above any method heretofore in
use. It is _imperishable_, giving a surface almost equal in hardness to
the glass itself. It is easy of application; it gives a brilliant finish;
it is not affected by a moist atmosphere; it is not affected by pure
water; it is the best article ever used for _finishing ambrotypes_; it
will preserve glass negatives for all time; it will preserve the _whites_
in the ambrotype; it gives a rich lustre to drapery; it will bear exposure
to the hot sun; it preserves positives and negatives from injury by light.
It is an article that, when once tried, the operator upon glass (positive,
negative, or albumenized plates) _will not do without_.

The ingredients in the composition of this gilding are neither _patented_
nor _published_, but it can be procured from any dealer in photographic
chemicals.


Nitrate of Silver Bath.

[Sidenote: NITRATE OF SILVER BATH.]

I here give what I consider an improvement on the bath mentioned in the
first edition of this work. I first published it in _Humphrey's Journal_,
No. 23, Vol. VII.:

The nitrate of silver solution is an important mixture in the chemical
department of the ambrotype process, and requires the especial care of
the operator in its preparation. I give the following as one of the most
approved for general practice. It is well adapted to the production of
positives, and its action is of great uniformity.

  Pure water                                          1 ounce.
  Nitrate of silver in crystals
    [neutral to acid test]                           45 grains.
  Nitric acid C. P. [Quantity as given below].

This proportion is to be observed for any quantity of solution. If I were
to prepare a bath 40 ounces, I would proceed as follows:

  Water                                              40 ounces.
  Nitrate of silver                                1800 grains.

Measure the water, and put into a two-quart bottle; then pour out 8 oz.
of it in a pint bottle, and into this put the whole of the nitrate of
silver (1800 gr.); shake it well until it is all dissolved. This forms a
concentrated solution--into which put the following prepared iodide of
silver:--

Dissolve in a 3 or 4 oz. bottle containing 1 oz. water, 10 gr. nitrate
of silver; and in another bottle or graduate containing a little water,
dissolve 10 grains of iodide of potassium; pour this into the 10 grain
solution of nitrate of silver, and a yellow substance (iodide of silver)
will precipitate; fill the bottle with water, and let it settle; then pour
off the water, leaving the yellow mass behind; again pour on it clean
water, shake it, and let it settle as before, and pour off again; repeat
this for about six changes of water.

Then it (the iodide of silver) is to be put into the bottle containing
the 8 oz. water and 1800 gr. of nitrate of silver; shake it well, and it
will nearly or quite all dissolve; pour this into the two-quart bottle,
and shake well; it will be of a yellowish white tint, and should be
filtered through asbestos or sponge, when it will become clear. When
clear, test the solution with blue litmus-paper; if it turns it red, it is
sufficiently acid; if it does not change it, add _one_ or _two_ drops of
nitric acid, chemically pure; then test it again; if it does not change
it, add _one_ or _two_ drops more, or just enough to change the paper to
the slightest red.

A solution prepared in this proportion will, like others, improve by age.
An old bath is considered far more valuable than one newly prepared. These
remarks may appear to old photographic operators as of no importance, but
they must bear in mind that there are hundreds just adopting this new
process of picture taking.

This solution will work more satisfactorily than the one I formerly used.
It will work quicker in the camera, and is _equally_ durable.

       *       *       *       *       *

Acknowledgment.--The following pages, under the head of _Vocabulary
of Photographic Chemicals_, and treating upon the Chemicals used in
Photography, are taken from the third edition of "Hardwich's Photographic
Chemistry:"--


=Vocabulary of Photographic Chemicals.=

[Sidenote: VOCABULARY OF PHOTOGRAPHIC CHEMICALS.]


Acetic Acid.

Symbol, C{4}H{3}O{3} + HO. Atomic weight, 60.

Acetic acid is a product of the _oxidation_ of alcohol. Spirituous
liquids, when perfectly pure, are not affected by exposure to air; but if
a portion of yeast, or nitrogenous organic matter of any kind, be added,
it soon acts as a _ferment_, and causes the spirit to unite with oxygen
derived from the atmosphere, and to become _sour_ from formation of acetic
acid or "vinegar."

Acetic acid is also produced on a large scale by heating _wood_ in close
vessels; a substance distils over which is acetic acid contaminated with
empyreumatic and tarry matter; it is termed pyroligneous acid, and is much
used in commerce.

The most concentrated acetic acid may be obtained by neutralizing common
vinegar with carbonate of soda and crystallizing out the acetate of soda
so formed; this acetate of soda is then distilled with sulphuric acid,
which removes the soda and liberates acetic acid: the acetic acid being
volatile, distils over, and may be condensed.

_Properties of Acetic Acid._--The strongest acid contains only a single
atom of water; it is sold under the name of "glacial acetic acid," so
called from its property of solidifying at a moderately low temperature.
At about 50° the crystals melt, and form a limpid liquid of pungent odor
and a density nearly corresponding to that of water; the specific gravity
of acetic acid, however, is no test of its real strength, which can only
be estimated by analysis.

The commercial glacial acetic acid is often diluted with water, which
may be suspected if it does not solidify during the cold winter months.
Sulphurous and hydrochloric acids are also common impurities. They are
injurious in photographic processes from their property of precipitating
nitrate of silver. To detect them proceed as follows:--dissolve a small
crystal of nitrate of silver in a few drops of water, and add to it about
half a drachm of the glacial acid; the mixture should remain quite clear
even when exposed to the light. Hydrochloric and sulphurous acids produce
a white deposit of chloride or sulphite of silver; and if _aldehyde_ or
volatile tarry matter be present in the acetic acid, the mixture with
nitrate of silver, although clear at first, becomes discolored by the
action of light.

Many photographers employ a cheaper form of acetic acid, sold by druggists
as "Beaufoy's" acid;[A] it should be of the strength of the acetic acid
fortiss. of the London Pharmacopoeia, containing 30 per cent, real acid,
and must be tested for sulphuric acid (see sulphuric acid), and also by
mixing with nitrate of silver.

[Footnote A: In this country the practitioner uses the article sold in
market as "Acetic Acid, No. 8."--S. D. H.]


Acetate of Silver. (_See_ Silver, Acetate of.)


Albumen.

Albumen is an organic principle, found both in the animal and vegetable
kingdom. Its properties are best studied in the _white of egg_, which is a
very pure form of albumen.

Albumen is capable of existing in two states; in one of which it is
soluble, in the other insoluble in water. The aqueous solution of the
soluble variety gives a slightly alkaline reaction to test-paper; it is
somewhat thick and glutinous, but becomes more fluid on the addition of a
small quantity of an alkali, such as potash or ammonia.

Soluble albumen may be converted into the insoluble form in the following
ways:--

1. _By the application of heat._--A moderately strong solution of albumen
becomes opalescent and coagulates on being heated to about 150°, but a
temperature of 212° is required if the liquid is very dilute. A layer of
_dried_ albumen cannot easily be coagulated by the mere application of
heat.

2. _By addition of strong acids._--Nitric acid coagulates albumen
perfectly without the aid of heat. Acetic acid, however, acts differently,
appearing to enter into combination with the albumen, and forming a
compound soluble in warm water acidified by acetic acid.

3. _By the action of metallic salts._--Many of the salts of the metals
coagulate albumen very completely. Nitrate of silver does so; also the
bichloride of mercury. Ammoniacal oxide of silver, however, does not
coagulate albumen.

The white precipitate formed on mixing albumen with nitrate of silver is
a chemical compound of the animal matter with protoxide of silver. This
substance, which has been termed albuminate of silver, is soluble in
ammonia and hyposulphite of soda; but after exposure to light, or heating
in a current of hydrogen gas, it assumes a brick-red color, being probably
reduced to the condition of a salt of the _suboxide_ of silver. It is then
almost insoluble in ammonia, but enough dissolves to tinge the liquid
wine-red. The author is of opinion that the _red coloration_ of solution
of nitrate of silver employed in sensitizing the albumenized photographic
paper is produced by the same compound, although often referred to the
presence of sulphuret of silver.

Albumen also combines with lime and baryta; and chloride of barium has
been recommended in positive printing upon albumenized paper, probably
from this cause.

_Chemical composition of albumen._--Albumen belongs to the _nitrogenous_
class of organic substances. It also contains small quantities of sulphur
and phosphorus.


Alcohol.

Symbol, C{4}H{6}O{2}. Atomic weight, 46.

Alcohol is obtained by the careful distillation of any spirituous or
fermented liquor. If wine or beer be placed in a retort, and heat applied,
the alcohol, being more volatile than water, rises first, and is condensed
in an appropriate receiver; a portion of the vapor of water, however,
passes over with the alcohol, and dilutes it to a certain extent, forming
what is termed "spirits of wine." Much of this water may be removed by
redistillation from carbonate of potash; but in order to render the
alcohol thoroughly _anhydrous_, it is necessary to employ _quick lime_
which possesses a still greater attraction for water. An equal weight of
this powdered lime is mixed with strong alcohol of ·823, and the two are
distilled together.

_Properties of Alcohol._--Pure anhydrous alcohol is a limpid liquid, of an
agreeable odor and pungent taste; sp. gr. at 60°, ·794. It absorbs vapor
of water, and becomes diluted by exposure to damp air; boils at 173° Fahr.
It has never been frozen.

Alcohol distilled from carbonate of potash has a specific gravity of ·815
to ·823, and contains 90 to 93 per cent, of real spirit.

The specific gravity of ordinary rectified spirits of wine is usually
about ·840, and it contains 80 to 83 per cent, of absolute alcohol.


Ammonia.

Symbol, NH{3} or NH{4}O. Atomic weight, 17.

The liquid known by this name is an aqueous solution of the volatile gas
ammonia. Ammoniacal gas contains 1 atom of nitrogen combined with three of
hydrogen: these two elementary bodies exhibit no affinity for each other,
but they can be made to unite under certain circumstances, and the result
is ammonia.

Properties of Ammonia.--Ammoniacal gas is soluble in water to a large
extent; the solution possessing those properties which are termed
alkaline. Ammonia, however, differs from the other alkalies in one
important particular--it is volatile: hence the original color of turmeric
paper affected by ammonia is restored on the application of heat. Solution
of ammonia absorbs carbonic acid rapidly from the air, and is converted
into carbonate of ammonia; it should therefore be preserved in stoppered
bottles. Besides carbonate, commercial ammonia often contains chloride of
ammonium, recognized by the white precipitate given by nitrate of silver
after acidifying with pure nitric acid.

The strength of commercial ammonia varies greatly; that sold for
pharmaceutica purposes, under the name of liquor ammoniæ, contains about
10 per cent, of real ammonia. The sp. gr. of aqueous ammonia diminishes
with the proportion of ammonia present, the liquor ammoniæ being usually
about ·936.

_Chemical Properties._--Ammonia, although forming a large class of
salts, appears at first sight to contrast strongly by composition with
the alkalies proper, such as potash and soda. Mineral bases generally
are _protoxides of metals_, but ammonia consists simply of nitrogen and
hydrogen united with oxygen. The following remarks may perhaps tend
somewhat to elucidate the difficulty:--

_Theory of Ammonium._--This theory supposes that a substance exists
possessing the properties of a metal, but different from metallic bodies
generally in being compound in structure: the formula assigned to it is
NH{4}, 1 atom of nitrogen united with 4 of hydrogen. The hypothetical
metal is termed "ammonium," and ammonia, associated with an atom of water,
may be viewed as its _oxide_; for NH{3} + HO plainly equals NH{4}O.
Thus, as potash is the oxide of _potassium_, so ammonia is the oxide of
_ammonium_.

The composition of the _salts_ of ammonia is on this view assimilated to
those of the alkalies proper. Thus, sulphate of ammonia is a sulphate of
the oxide of _ammonium_; muriate or hydrochlorate of ammonia is a chloride
of ammonium, etc.


Ammonio-Nitrate of Silver.

(_See_ Silver, Ammonio-Nitrate of.)


Aqua-Regia. (_See_ Nitro-Hydrochloric Acid.)


Baryta, Nitrate of. (_See_ Nitrate of Baryta.)


Bichloride of Mercury.

(_See_ Mercury, Bichloride of.)


Bromine.

Symbol, Br. Atomic weight, 78.

This elementary substance is obtained from the uncrystallizable residuum
of sea-water, termed _bittern_. It exists in the water in very minute
proportion, combined with magnesium in the form of a soluble bromide of
magnesium.

_Properties._--Bromine is a deep reddish-brown liquid of a disagreeable
odor, and fuming strongly at common temperatures; sparingly soluble in
water (1 part in 23, Lowig), but more abundantly so in alcohol, and
especially in ether. It is very heavy, having a specific gravity of 3·0.

Bromine is closely analogous to chlorine and iodine in its chemical
properties. It stands on the list intermediately between the two; its
affinities being stronger than those of iodine, but weaker than chlorine.
(_See_ chlorine.)

It forms a large class of salts, of which the bromides of potassium,
cadmium, and silver are the most familiar to photographers.


Bromide of Potassium.

Symbol, KBr. Atomic weight, 118.

Bromide of potassium is prepared by adding bromine to caustic potash,
and heating the product, which is a mixture of bromide of potassium and
bromate of potash, to redness, in order to drive off the oxygen from the
latter salt. It crystallizes in anhydrous cubes, like the chloride, and
iodide, of potassium; it is easily soluble in water, but more sparingly so
in alcohol; it yields red fumes of bromine when acted upon by sulphuric
acid.


Bromide of Silver. (_See_ Silver, Bromide of.)


Carbonate of Soda.

Symbol, NaO CO{2} + 10 Aq.

This salt was formerly obtained from the ashes of seaweeds, but is
now more economically manufactured on a large scale from common salt.
The chloride of sodium is first converted into sulphate of soda, and
afterwards the sulphate into carbonate of soda.

_Properties._--The perfect crystals contain ten atoms of water, which
are driven off by the application of heat, leaving a white powder--the
anhydrous carbonate. _Common washing soda_ is a neutral carbonate,
contaminated to a certain extent with chloride of sodium and sulphate of
soda. The carbonate used for effervescing draughts is either a bicarbonate
with 1 atom of water, or a sesquicarbonate, containing about 40 per cent,
of real alkali; it is therefore nearly double as strong as the washing
carbonate, which contains about 22 per cent, of soda. Carbonate of soda is
soluble in twice its weight of water at 60°, the solution being strongly
alkaline.


Carbonate of Potash. (_See_ Potash, Carbonate of.)


Caseine. (_See_ Milk.)


Charcoal, Animal.

Animal charcoal is obtained by heating animal substances, such as bones,
dried blood, horns, etc., to redness, in close vessels, until all
volatile empyreumatic matters have been driven off, and a residue of
carbon remains. When prepared from bones it contains a large quantity of
inorganic matter in the shape of carbonate and phosphate of lime, the
former of which produces _alkalinity_ in reacting upon nitrate of silver.
Animal charcoal is freed from these earthy salts by repeated digestion in
hydrochloric acid; but unless very carefully washed it is apt to retain
an acid reaction, and so to liberate free nitric acid when added to
solution of nitrate of silver.

_Properties._--Animal charcoal, when pure, consists solely of carbon, and
burns away in the air without leaving any residue: it is remarkable for
its property of decolorizing solutions; the organic coloring substance
being separated, but not actually _destroyed_, as it is by _chlorine_
employed as a bleaching agent. This power of absorbing coloring matter is
not possessed in an equal degree by all varieties of charcoal, but is in
great measure peculiar to those derived from the animal kingdom.


China Clay or Kaolin.

This is prepared, by careful levigation, from mouldering granite and
other disintegrated felspathic rocks. It consists of the _silicate of
alumina_,--that is, of silicic acid or _flint_, which is an oxide of
silicon, united with the base alumina (oxide of aluminum). Kaolin is
perfectly insoluble in water and acids, and produces no decomposition
in solution of nitrate of silver. It is employed by photographers to
decolorize solutions of nitrate of silver which have become brown from the
action of albumen or other organic matters.


Chlorine.

Symbol, Cl. Atomic weight, 36.

Chlorine is a chemical element found abundantly in nature, combined with
metallic sodium in the form of chloride of sodium, or sea-salt.

_Preparation._--By distilling common salt with sulphuric acid, sulphate
of soda and hydrochloric acid are formed. Hydrochloric acid contains
chlorine combined with hydrogen; by the action of _nascent_ oxygen (see
oxygen), the hydrogen may be removed in the form of water, and the
chlorine left alone.

_Properties._--Chlorine is a greenish-yellow gas, of a pungent and
suffocating odor; soluble to a considerable extent in water, the solution
possessing the odor and color of the gas. It is nearly 2-1/2 times as
heavy as a corresponding bulk of atmospheric air.

_Chemical Properties._--Chlorine belongs to a small natural group of
elements which contains also bromine, iodine, and fluorine. They are
characterized by having a strong affinity for hydrogen, and also for
the metals, but are comparatively indifferent to oxygen. Many metallic
substances actually undergo _combustion_ when projected into an atmosphere
of chlorine, the union between the two taking place with extreme violence.
The characteristic bleaching properties of chlorine gas are explained in
the same manner:--Hydrogen is removed from the organic substance, and in
that way the structure is broken up and the color destroyed.

Chlorine is more powerful in its affinities than either bromine or
iodine. The salts formed by these three elements are closely analogous
in composition and often in properties. Those of the alkalies, alkaline
earths, and many of the metals are soluble in water, but the silver salts
are insoluble; the lead salts sparingly so.

The combinations of chlorine, bromine, iodine, and fluorine, with
hydrogen, are acids, and neutralize alkalies in the usual manner, with
formation of alkaline chloride and water.

The test by which the presence of chlorine is detected, either free or
in combination with bases, is _nitrate of silver_; it gives a white curdy
precipitate of chloride of silver, insoluble in nitric acid, but soluble
in ammonia. The solution of nitrate of silver employed as the test must
not contain iodide of silver, as this compound is precipitated by dilution.


Chloride of Ammonium.

Symbol, NH{4}Cl. Atomic weight, 54.

This salt, also known as muriate or hydrochlorate of ammonia, occurs
in commerce in the form of colorless and translucent masses, which are
procured by _sublimation_, the dry salt being volatile when strongly
heated. It dissolves in an equal weight of boiling, or in three parts of
cold water. It contains more _chlorine_ in proportion to the weight used
than chloride of sodium, the atomic weights of the two being as 54 to 60.


Chloride of Barium.

Symbol, BaCl+2HO. Atomic weight, 123.

Barium is a metallic element, very closely allied to calcium, the
elementary basis of _lime_. The chloride of barium is commonly employed as
a test for sulphuric acid, with which it forms an insoluble precipitate
of sulphate of baryta. It is also said to affect the color of the
photographic image when used in preparing positive paper; which may
possibly be due to a chemical combination of baryta with albumen: but
it must be remembered that this chloride, from its high atomic weight,
contains _less_ chlorine than the alkaline chlorides.

_Properties of Chloride of Barium._--Chloride of barium occurs in the
form of white crystals, soluble in about two parts of water, at common
temperature. These crystals contain two atoms of water of crystallization,
which are expelled at 212°, leaving the anhydrous chloride.


Chloride of Gold. (_See_ Gold, Chloride of.)


Chloride of Sodium.

Symbol, NaCl. Atomic weight, 60.

Common salt exists abundantly in nature, both in the form of solid
rock-salt and dissolved in the waters of the ocean.

_Properties of the pure Salt._--Fusible without decomposition at low
redness, but sublimes at higher temperatures; the melted salt concretes
into a hard white mass on cooling. Nearly insoluble in absolute alcohol,
but dissolves in minute quantity in rectified spirit. Soluble in three
parts of water, both hot and cold. Crystallizes in cubes, which are
anhydrous.

_Impurities of Common Salt._--Table salt often contains large quantities
of the chlorides of magnesium and calcium, which, being deliquescent,
produce a dampness by absorption of atmospheric moisture: sulphate of
soda is also commonly present. The salt may be purified by repeated
recrystallization, but it is more simple to prepare the pure compound
_directly_, by neutralizing hydrochloric acid with carbonate of soda.


Chloride of Silver. (_See_ Silver, Chloride of.)


Citric Acid.

This acid is found abundantly in lemon-juice and in lime-juice. It occurs
in commerce in the form of large crystals, which are soluble in less than
their own weight of water at 60°.

Commercial citric acid is sometimes mixed with tartaric acid. The
adulteration may be discovered by making a concentrated solution of the
acid and adding _acetate of potash_; crystals of bitartrate of potash will
separate if tartaric acid be present.

Citric acid is tribasic. It forms with silver a white insoluble salt,
containing 3 atoms of oxide of silver to 1 atom of citric acid. If the
citrate of silver be heated in a current of hydrogen gas, a part of the
acid is liberated and the salt is reduced to a citrate of _suboxide_ of
silver; which is of a red color. The action of white light in reddening
citrate of silver is shown by the author to be of a similar nature.


Cyanide of Potassium.

Symbol, K, C{2}N, or KCy. Atomic weight, 66.

This salt is a compound of cyanogen gas with the metal potassium. Cyanogen
is not an elementary body, like chlorine or iodine, but consists of carbon
and nitrogen united in a peculiar manner. Although a compound substance,
it reacts in the manner of an element, and is therefore (like _ammonium_,
previously described) an exception to the usual laws of chemistry. Many
other bodies of a similar character are known.


Ether.

Symbol, C{4}H{5}O. Atomic weight, 37.

Ether is obtained by distilling a mixture of sulphuric acid and alcohol.
If the formula of alcohol (C{4}H{6}O{2}) be compared with that of ether,
it will be seen to differ from it in the possession of an additional atom
of hydrogen and of oxygen: in the reaction, the sulphuric acid removes
these elements in the form of water, and by so doing converts one atom
of alcohol into an atom of ether. The term _sulphuric_ applied to the
commercial ether has reference only to the manner of its formation.

_Properties of Ether._--It is neither acid nor alkaline to test-paper.
Specific gravity, at 60°, about ·720. Boils at 98° Fahrenheit. The vapor
is exceedingly dense, and may be seen passing off from the liquid and
falling to the ground: hence the danger of pouring ether from one bottle
to another if a flame be near at hand.

Ether does not mix with water in all proportions; if the two are shaken
together, after a short time the former rises and floats upon the surface.
In this way a mixture of ether and alcohol may be purified to some extent,
as in the common process of _washing_ ether. The water employed however
always retains a certain portion of ether (about a tenth part of its
bulk), and acquires a strong ethereal odor; washed ether also contains
water in small quantity.

Bromine and iodine are both soluble in ether, and gradually react upon and
decompose it.

The strong alkalies, such as potash and soda, also decompose ether
slightly after a time, but not immediately. Exposed to air and light,
ether is oxidized and acquires a peculiar odor.

Ether dissolves fatty and resinous substances readily, but inorganic salts
are mostly insoluble in this fluid. Hence it is that iodide of potassium
and other substances dissolved in alcohol are precipitated to a certain
extent by the addition of ether.


Fluoride of Potassium.

Symbol, KF. Atomic weight, 59.

_Preparation._--Fluoride of potassium is formed by saturating hydrofluoric
acid with potash, and evaporating to dryness in a platinum vessel.
_Hydrofluoric acid_ contains fluorine combined with hydrogen; it is a
powerfully acid and corrosive liquid, formed by decomposing flour spar,
which is a _fluoride of calcium_, with strong sulphuric acid; the action
which takes place being precisely analogous to that involved in the
preparation of hydrochloric acid.

_Properties._--A deliquescent salt, occurring in small and imperfect
crystals. Very soluble in water: the solution acting upon glass in the
same manner as hydrofluoric acid.


Formic Acid.

Symbol, C{2}HO{3}. Atomic weight, 37.

This substance was originally discovered in the _red ant_ (_Formica
rufa_), but it is prepared on a large scale by distilling _starch_ with
binoxide of manganese and sulphuric acid.

_Properties._--The strength of commercial formic acid is uncertain, but
it is always more or less dilute. The strongest acid, as obtained by
distilling formiate of soda with sulphuric acid, is a fuming liquid with a
pungent odor, and containing only one atom of water: it inflames the skin
in the same manner as the sting of the ant.

Formic acid reduces the oxides of gold, silver, and mercury, to the
metallic state, and is itself oxidized into carbonic acid. The alkaline
formiates also possess the same properties.


Gelatine.

Symbol, C{13}H{10}O{5}N{2}. Atomic weight, 156.

This is an organic substance somewhat analogous to albumen, but differing
from it in properties. It is obtained by subjecting bones, hoofs, horns,
calves' feet, etc., to the action of boiling water. The jelly formed
on cooling is termed size, or when dried or cut into slices, _glue_.
Gelatine, as it is sold in the shops, is a pure form of glue. _Isinglass_
is gelatine prepared, chiefly in Russia, from the air-bladders of certain
species of sturgeon.

_Properties of Gelatine._--Gelatine softens and swells up in cold water,
but does not _dissolve_ until heated: the hot solution, on cooling, forms
a tremulous jelly. One ounce f cold water will retain about three grains
of isinglass without gelatinizing; but much depends upon the temperature,
a few degrees greatly affecting the result.

Gelatine forms no compound with oxide of silver analogous to the
albuminate of silver; which fact explains the difference in the
photographic properties of albumen and gelatine.


Glycerine.

Fatty bodies are resolved by treatment with an alkali into an acid--which
combines with the alkali, forming a _soap_,--and glycerine, remaining in
solution.

Pure glycerine, as obtained by Price's patent process of distillation,
is a viscid liquid of sp. gr. about 1·23; miscible in all proportions
with water and alcohol. It is peculiarly a neutral substance, exhibiting
no tendency to combine with acids or bases. It has little or no action
upon nitrate of silver in the dark, and reduces it very slowly even when
exposed to light.


Gold, Chloride of.

Symbol, AuCl{3}. Atomic weight, 303.

This salt is formed by dissolving pure metallic gold in nitro-hydrochloric
acid, and evaporating at a gentle heat. The solution affords deliquescent
crystals of a deep orange color.

Chloride of gold, in a state fit for photographic use may easily be
obtained by the following process:--Place a half-sovereign in any
convenient vessel, and pour on it half a drachm of nitric acid mixed with
two and a half drachms of hydrochloric acid and three drachms of water;
digest by a gentle heat, but do not _boil_ the acid, or much of the
chlorine will be driven off in the form of gas. At the expiration of a few
hours add fresh aqua-regia in quantity the same as at first, which will
probably complete the solution, but if not, repeat the process a third
time.

Lastly, neutralize the liquid by adding carbonate of soda until all
effervescence ceases, and a green precipitate forms; this is _carbonate of
copper_, which must be allowed several hours to separate thoroughly. The
solution then contains chloride of gold in a neutral state, and free from
copper and silver, with which the metallic gold is alloyed in the standard
coin of the realm.

The weight of a half-sovereign is about 61 grains, of which 56 grains are
pure gold. This is equivalent to 86 grains of chloride of gold, which will
therefore be the quantity contained in the solution.

The following process for preparing chloride of gold is more perfect than
the last:--dissolve the gold coin in aqua-regia as before; then boil with
excess of hydrochloric acid to destroy the nitric acid, dilute largely
with distilled water, and add a filtered aqueous solution of common
sulphate of iron (6 parts in 1 part of gold); collect the precipitated
gold, which is now free from copper; re-dissolve in aqua-regia, and
evaporate to dryness on a water bath.

Avoid using ammonia to neutralize chloride of gold, as it would be liable
to occasion a deposit of "fulminating gold," the properties of which are
described immediately following.

_Properties of Chloride of Gold._--As sold in commerce it usually contains
excess of hydrochloric acid, and is then of a bright yellow color; but
when neutral and somewhat concentrated it is dark red (_Leo ruber_ of the
alchemists). It gives no precipitate with carbonate of soda, unless heat
be applied; the free hydrochloric acid present forms, with the alkali,
chloride of sodium, which unites with the chloride of gold, and produces a
double salt, chloride of gold and sodium, soluble in water.

Chloride of gold is decomposed with precipitation of metallic gold by
charcoal, sulphurous acid, and many of the vegetable acids; also by
protosulphate and protonitrate of iron. It tinges the cuticle of an
indelible purple tint. It is soluble in alcohol and in ether.


Gold, Fulminating.

This is a yellowish-brown substance, precipitated on adding ammonia to a
strong solution of chloride of gold.

It may be dried carefully at 212°, but _explodes violently_ on being
heated suddenly about to 290°. Friction also causes it to explode when
dry; but the moist powder may be rubbed or handled without danger. It is
decomposed by sulphuretted hydrogen.

Fulminating gold is probably an aurate of ammonia, containing 2 atoms of
ammonia to 1 atom of peroxide of gold.


Gold, Hyposulphite of.

Symbol, AuO S{2}O{2}. Atomic Weight, 253.

Hyposulphite of gold is produced by the reaction of chloride of gold upon
hyposulphite of soda.

The salt sold in commerce as sel d'or is a double hyposulphite of gold and
soda, containing one atom of the former salt to three of the latter, with
four atoms of water of crystallization. It is formed by adding one part of
chloride of gold, in solution, to three parts of hyposulphite of soda, and
precipitating the resulting salt by alcohol; the chloride of gold must be
added to the hyposulphite of soda, and not the soda salt to the gold.

_Properties._--Hyposulphite of gold is unstable and cannot exist in an
isolated state, quickly passing into sulphur, sulphuric acid, and metallic
gold. When combined with excess of hyposulphite of soda in the form of sel
d'or, it is more permanent.

Sel d'or occurs crystallized in fine needles, which are very soluble in
water. The commercial article is often impure, containing little else than
hyposulphite of soda, with a trace of gold. It may be analyzed by adding
a few drops of strong nitric acid (free from chlorine) diluting with
water, and afterwards collecting and igniting the yellow powder, which is
metallic gold.


Grape Sugar.

Symbol, C{24}H{28}O{28}. Atomic weight, 366.

This modification of sugar, often termed _granular sugar_, or _glucose_,
exists abundantly in the juice of grapes, and in many other varieties of
fruit. It forms the saccharine concretion found in honey, raisins, dried
figs, etc. It may be produced artificially by the action of fermenting
principles, and of dilute mineral acids, upon starch.

_Properties._--Grape sugar crystallizes slowly and with difficulty from
a concentrated aqueous solution, in small hemispherical nodules, which
are hard, and feel gritty between the teeth. It is much less sweet to
the taste than cane sugar, and not so soluble in Water (1 part dissolves
in 1-1/2 of cold water). Grape sugar tends to absorb oxygen, and hence
it possesses the property of decomposing the salts of the noble metals,
and reducing them by degrees to the metallic state, even without the aid
of lights The action however in the case of _nitrate of silver_ is slow,
unless the temperature be somewhat elevated. _Cane_ sugar does not possess
these properties to an equal extent, and hence it is readily distinguished
from the other variety.


Honey.

This substance contains two distinct kinds of sugar, grape sugar, and an
uncrystallizable substance analogous to, or identical with, the treacle
found associated with common sugar in the cane juice. The agreeable
taste of honey probably depends upon the latter, but its reducing power
on metallic oxides is due to the former. Pure grape sugar can readily
be obtained from inspissated honey, by treating it with alcohol, which
dissolves out the syrup, but leaves the crystalline portion.


Hydrochloric; Acid.

Symbol, HCl. Atomic weight, 37.

Hydrochloric acid is a volatile gas, Which may be liberated from the
salts termed chlorides by the action of sulphuric acid. The acid, by its
superior affinities, removes the base; thus,--

  NaCl + HO SO{3} = NaO SO{3} + HCl.

_Properties._--Abundantly soluble in water, forming the liquid
hydrochloric or muriatic acid of commerce. The most concentrated solution
of hydrochloric acid has a sp. gr. 1·2, and contains about 40 per cent, of
gas; that commonly sold is somewhat weaker, sp; gr. 1·14 = 28 per cent.
real acid.

Pure hydrochloric acid is colorless, and fumes in the air. The yellow
color of the commercial acid depends upon the presence of traces of
perchloride of iron or organic matter; commercial muriatic acid also often
contains a portion of free chlorine and of sulphuric acid.


Hydriodic Acid.

Symbol, HI. Atomic weight, 127.

This is a gaseous compound of hydrogen and iodine, corresponding in
composition to the hydrochloric acid. It cannot, however, from its
instability, be obtained in the same manner, since, on distilling
an iodide with sulphuric acid, the hydriodic acid first formed is
subsequently decomposed into iodine and hydrogen. An aqueous solution of
hydriodic acid is easily prepared by adding iodine to water containing
sulphuretted hydrogen gas; a decomposition takes place, and sulphur is set
free; thus: HS + I = HI + S.

_Properties._--Hydriodic acid is very soluble in water, yielding a
strongly acid liquid. The solution, colorless at first, soon becomes brown
from decomposition, and liberation of free iodine. It may be restored to
its original condition by adding solution of sulphuretted hydrogen.


Hydrosulphuric Acid.

Symbol, HS. Atomic weighty 17.

This substance, also known as sulphuretted hydrogen, is a gaseous compound
of sulphur and hydrogen, analogous in composition to hydrochloric and
hydriodic acids. It is usually prepared by the action of dilute sulphuric
acid upon sulphuret of iron, the decomposition being similar to that
involved in the preparation of the hydrogen acids generally:--

  FeS + HO SO{3} = FeO SO{3} + HS.

_Properties._--Cold water absorbs three times its bulk of hydrosulphuric
acid, and acquires the peculiar putrid odor and poisonous qualities of the
gas. The solution is faintly acid to test-paper, and becomes opalescent on
keeping, from gradual separation of sulphur. It is decomposed by nitric
acid, and also by chlorine and iodine. It precipitates silver from its
solutions, in the form of black sulphuret of silver; also copper, mercury,
lead, etc.; but iron and other metals of that class are not affected, if
the liquid contains free acid. Hydrosulphuric acid is constantly employed
in the chemical laboratory for these and other purposes.


Hydrosulphate of Ammonia.

Symbol, NH{4}S HS. Atomic weight, 51.

The liquid known by this name, and formed by passing sulphuretted hydrogen
gas into ammonia, is a double sulphuret of hydrogen and ammonium. In the
preparation, the passage of the gas is to be continued until the solution
gives no precipitate with sulphate of magnesia and smells strongly of
hydrosulphuric acid.

Properties,--Colorless at first, but afterwards changes to yellow, from
liberation and subsequent solution of sulphur. Becomes milky on the
addition of any acid. Precipitates, in the form of sulphuret, all the
metals which are affected by sulphuretted hydrogen; and, in addition,
those of the class to which iron, zinc, and manganese, belong.

Hydrosulphate of ammonia is employed in photography to darken the negative
image, and also in the preparation of iodide of ammonium; the separation
of silver from hyposulphite solutions, etc.


Hyposulphite of Soda.

Symbol, NaO S{2}H{2} + 5 HO. Atomic weight, 125.

The hyposulphite of soda commonly employed by photographers is a neutral
combination of hyposulphurous acid and the alkali soda. It is selected as
being more economical in preparation than any other hyposulphite adapted
for fixing.

Hyposulphite of soda occurs in the form of large translucent groups of
crystals, which include five atoms of water. These crystals are soluble
in water almost to any extent, the solution being attended with the
production of cold; they have a nauseous and bitter taste.


Hyposulphite of Gold. (_See_ Gold, Hyposulphite of.)


Hyposulphite of Silver. (_See_ Silver, Hyposulphite of.)


Iceland Moss.

_Cetraria Islandica._--A species of lichen found in Iceland and the
mountainous parts of Europe; when boiled in water, it first swells up, and
then yields a substance which gelatinizes on cooling.

It contains lichen starch; a bitter principle soluble in alcohol, termed
"cetrarine;" and common starch; traces of gallic acid and bitartrate of
potash are also present.


Iodine.

Symbol, I. Atomic weight, 126.

Iodine is chiefly prepared at Glasgow, from _kelp_, which is the fused
ash obtained by burning seaweeds. The waters of the ocean contain minute
quantities of the iodides of sodium and magnesium, which are separated and
stored up by the growing tissues of the marine plant.

In the preparation, the mother-liquor of kelp is evaporated to dryness
and distilled with sulphuric acid; the hydriodic acid first liberated is
decomposed by the high temperature, and fumes of iodine condense in the
form of opaque crystals.

_Properties._--Iodine has a bluish-black color and metallic lustre; it
stains the skin yellow, and has a pungent smell, like diluted chlorine.
It is extremely volatile when moist, boils at 350°, and produces dense
violet-colored fumes, which condense in brilliant plates. Specific gravity
4·946. Iodine is very sparingly soluble in water, 1 part requiring 7000
parts for perfect solution: even this minute quantity however tinges the
liquid of a brown color. Alcohol and ether dissolve it more abundantly,
forming dark-brown solutions. Iodine also dissolves freely in solutions of
the alkaline iodides, such as the iodide of potassium, of sodium, and of
ammonium.

_Chemical Properties._--Iodine belongs to the chlorine group of elements,
characterized by forming acids with hydrogen, and combining extensively
with the metals (see chlorine). They are however comparatively indifferent
to oxygen, and also to each other. The iodides of the alkalies and
alkaline earths are soluble in water; also those of iron, zinc, cadmium,
etc. The iodides of lead, silver, and mercury are nearly or quite
insoluble.

Iodine possesses the property of forming a compound of a deep blue color
with starch. In using this as a test, it is necessary first to liberate
the iodine (if in combination), by means of chlorine, or nitric acid
saturated with peroxide of nitrogen. The presence of alcohol or ether
interferes to a certain extent with the result.


Iodide of Ammonium.

Symbol, NH{4}I. Atomic weight, 144.

This salt may be prepared by adding carbonate of ammonia to iodide of
iron, but more easily by the following process:--A strong solution of
hydrosulphate of ammonia is first made, by passing sulphuretted hydrogen
gas into liquor ammoniæ To this liquid iodine is added until the whole
of the sulphuret of ammonium has been converted into iodide. When this
point is reached, the solution at once colors brown from solution of free
iodine. On the first addition of the iodine, an escape of sulphuretted
hydrogen gas and a dense deposit of sulphur take place. After the
decomposition of the hydrosulphate of ammonia is complete, a portion of
hydriodic acid--formed by the mutual reaction of sulphuretted hydrogen
and iodine--attacks any carbonate of ammonia which may be present, and
causes an effervescence. The effervescence being over, the liquid is still
acid to test-paper, from excess of hydriodic acid; it is to be cautiously
neutralized with ammonia, and evaporated by the heat of a water-bath to
the crystallizing point.

The crystals should be thoroughly dried over a dish of sulphuric acid,
and then sealed in small tubes containing each about half a drachm of the
salt; by this means it will be preserved colorless.

Iodide of ammonium is very soluble in alcohol, but it is not advisable
to keep it in solution, from the rapidity with which it decomposes and
becomes brown.

The most common impurity of commercial iodide of ammonium is sulphate of
ammonia; it is detected by its sparing insolubility in alcohol.


Iodide of Cadmium.

Symbol, CdI. Atomic weight, 182.

This salt is formed by heating filings of metallic cadmium with iodine,
or by mixing the two together with addition of water. It is useful in
iodizing collodion intended for keeping, since it does not become brown
from liberation of free iodine with the same rapidity as the alkaline
iodides.

Iodide of cadmium is very soluble both in alcohol and water; the solution
yielding on evaporation large six-sided tables of a pearly lustre,
which are permanent in the air. The crystalline form of this salt is a
sufficient criterion of its purity.


Iodide of Iron.

Symbol, FeI. Atomic weight, 154.

Iodide of iron, in a fit state for photographic use, is easily obtained by
dissolving a drachm of iodine in an ounce of _proof spirit_--that is, a
mixture of equal bulks of spirits of wine and water--and adding an excess
of iron filings. After a few hours, a green solution is obtained without
the aid of heat. The presence of metallic iron in excess prevents the
liberation of iodine and deposit of peroxide of iron which would otherwise
speedily occur. It is very soluble in water and alcohol, but the solution
rapidly absorbs oxygen and deposits peroxide of iron; hence the importance
of preserving it in contact with metallic iron, with which the separated
iodine may recombine. By very careful evaporation, hydrated crystals of
protoiodide may be obtained, but the composition of the solid salt usually
sold under that name cannot be depended on.

The _periodide_ of iron, corresponding to the perchloride, has not been
examined, and it is doubtful if any such compound exists.


Iodide of Potassium.

Symbol, KI. Atomic weight, 166.

This salt is usually formed by dissolving iodine in solution of potash
until it begins to acquire a brown color; a mixture of iodide of potassium
and _iodate of potash_ (KO IO{5}) is thus formed; but by evaporation
and heating to redness, the latter salt parts with its oxygen, and is
converted into iodide of potassium.

_Properties._--It forms cubic and prismatic crystals, which should be
hard, and _very slightly or not at all deliquescent_. Soluble in less than
an equal weight of water at 60°; it is also soluble in alcohol, but not
in ether. The proportion of iodide of potassium contained in a saturated
alcoholic solution, varies with the strength of the spirit,--with
common spirits of wine, sp. gr. ·836, it would be about 8 grains to the
drachm; with alcohol rectified from carbonate of potash, sp. gr. ·823,
4 or 5 grains: with absolute alcohol, 1 to 2 grains. The solution of
iodide of potassium is instantly colored brown by free chlorine; also
very rapidly by peroxide of nitrogen; ordinary acids, however, act less
quickly, hydriodic acid being first formed, and subsequently decomposing
spontaneously.

Iodide of potassium, as sold in the shops, is often contaminated with
various impurities. The first and most remarkable is _carbonate of
potash_. When a sample of iodide of potassium contains much carbonate
of potash, it forms small and imperfect crystals, which are strongly
alkaline to test-paper, and become moist on exposure to the air, from the
deliquescent nature of the alkaline carbonate. _Sulphate of potash_ is
also a common impurity; it may be detected by chloride of barium.

_Chloride of potassium_ is another impurity; it is detected as
follows:--Precipitate the salt by an equal weight of nitrate of silver,
and treat the yellow mass with solution of ammonia; if any chloride of
silver is present, it dissolves in the ammonia, and after nitration is
re-precipitated in white curds by the addition of an excess of pure nitric
acid. If the nitric acid employed is not pure, but contains traces of free
chlorine, the iodide of silver must be well washed with distilled water
before treating it with ammonia, or the excess of free nitrate of silver
dissolving in the ammonia would, on neutralizing, produce chloride of
silver, and so cause an error.

_Iodide of potash_ is a fourth impurity often found in iodide of
potassium: to detect it, add a drop of dilute sulphuric acid, or a crystal
of citric acid, to the solution of the iodide; when, if much iodate be
present, the liquid will become yellow from liberation of free iodine.
The rationale of this reaction is as follows:--The sulphuric acid unites
with the base of the salt, and liberates hydriodic acid (HI), _a colorless
compound_; but if iodic acid (IO{5}) be also present, it decomposes the
hydriodic acid first formed, oxidizing the hydrogen into water (HO),
and setting free the iodine. The immediate production of a yellow color
on adding a weak acid to aqueous solution of iodide of potassium is,
therefore, a proof of the presence of an iodate. As iodate of potash is
thought to render collodion insensitive (?), this point should be attended
to.

Iodide of potassium may be rendered very pure by recrystallizing from
spirit, or by dissolving in strong alcohol of sp. gr. ·823, in which
sulphate, carbonate, and iodate of potash are insoluble. The proportion
of iodide of potassium contained in saturated alcoholic solutions varies
with the strength of the spirit.

Solution of chloride of barium is commonly used to detect impurities in
iodide of potassium; it forms a white precipitate if carbonate, iodate,
or sulphate be present. In the two former cases the precipitate dissolves
on the addition of _pure_ dilute nitric acid, but in the latter it is
insoluble. The commercial iodide, however, is rarely so pure as to remain
quite clear on the addition of chloride of barium, a _mere opalescence_,
therefore, may be disregarded.


Iodide of Silver. (_See_ Silver, Iodide of.)


Iron, Protosulphate of.

Symbol, FeO SO{3} + 7 HO. Atomic weight, 139.

This salt, often termed _copperas_ or _green vitriol_, is a most abundant
substance, and used for a variety of purposes in the arts. Commercial
sulphate of iron, however, being prepared on a large scale, requires
recrystallization to render it sufficiently pure for photographic purposes.

Pure sulphate of iron occurs in the form of large, transparent prismatic
crystals, of a delicate green color: by exposure to the air they gradually
absorb oxygen and become rusty on the surface. Solution of sulphate of
iron, colorless at first, afterwards changes to a red tint, and deposits
a brown powder; this powder is a _basic_ persulphate of iron, that is, a
persulphate containing an excess of the oxide or _base_. By the addition
of sulphuric or acetic acid to the solution, the formation of a _deposit_
is prevented, the brown powder being soluble in acid liquids.

The crystals of sulphate of iron include a large quantity of water of
crystallization, a part of which they lose by exposure to dry air. By a
higher temperature, the salt may be rendered perfectly _anhydrous_, in
which state it forms a white powder.

Aqueous solution of sulphate of iron absorbs the _binoxide of nitrogen_,
acquiring a deep olive-brown color: as this gaseous binoxide is itself a
reducing agent, the liquid so formed has been proposed as a more energetic
developer than the sulphate of iron alone.


Iron, Protonitrate of.

Symbol, FeO NO{5} + 7 HO. Atomic weight, 153.

This salt, by careful evaporation _in vacuo_ over sulphuric acid, forms
transparent crystals, of a light green color, and containing 7 atoms
of water, like the protosulphate. It is exceedingly unstable, and soon
becomes red from decomposition, unless preserved from contact with air.

The following process is commonly followed for preparing protonitrate of
iron:--

Take of nitrate of baryta 300 grains; powder and dissolve by the aid of
heat in three ounces of water; then throw in, by degrees, with constant
stirring, crystallized sulphate of iron, _powdered_, 320 grains. Continue
to stir for about five or ten minutes. Allow to cool, and filter from the
white deposit, which is the insoluble sulphate of baryta.

In place of nitrate of baryta, the nitrate of lead may be used (sulphate
of lead being an insoluble salt), but the quantity required will be
different. The atomic weights of nitrate of baryta and nitrate of lead are
as 131 to 166; consequently 300 grains of the former are equivalent to 380
grains of the latter.


Iron, Perchloride of.

Symbol, Fe{2}Cl{3}. Atomic weight, 164.

There are two chlorides of iron, corresponding in composition to the
protoxide and the sesquioxide respectively. The protochloride is very
soluble in water, forming a green solution, which precipitates a dirty
white protoxide on the addition of an alkali. The perchloride, on the
other hand, is dark brown, and gives a foxy-red precipitate with alkalies.

_Properties._--Perchloride of iron may be obtained in the solid form by
heating iron wire in excess of chlorine; it condenses in the shape of
brilliant and iridescent brown crystals, which are volatile, and dissolve
in water, the solution being acid to test-paper. It is also soluble in
alcohol, forming the _tinctura ferri sesquichloridi_ of the Pharmacopoeia.
Commercial perchloride of iron ordinarily contains an excess of
hydrochloric acid.


Litmus.

Litmus is a vegetable substance, prepared from various _lichens_, which
are principally collected on rocks adjoining the sea. The coloring matter
is extracted by a peculiar process, and afterwards made up into a paste
with chalk, plaster of Paris, &c.

Litmus occurs in commerce in the form of small cubes, of a fine violet
color. In using it for the preparation of test-papers, it is digested
in hot water, and sheets of porous paper are soaked in the blue liquid
so formed. The red papers are prepared at first in the same manner, but
afterwards placed in water which has been rendered faintly acid with
sulphuric or hydrochloric acid.


Mercury, Bichloride of.

Symbol, HgCl{2}. Atomic weight, 274.

This salt, also called corrosive sublimate, and sometimes _chloride of
mercury_ (the atomic weight of mercury being halved), may be formed by
heating mercury in excess of chlorine, or, more economically, by subliming
a mixture of persulphate of mercury and chloride of sodium.

_Properties._--a very corrosive and poisonous salt, usually sold in
semi-transparent, crystalline masses, or in the state of powder. Soluble
in 16 parts of cold, and in 3 of hot water; more abundantly so in alcohol,
and also in ether. The solubility in water may be increased almost to any
extent by the addition of free hydrochloric acid.

The protochloride of mercury is an insoluble white powder, commonly known
under the name of _calomel_.


Milk.

The milk of herbivorous animals contains three principal
constituents--fatty matter, caseine, and sugar; in addition to these,
small quantities of the chloride of potassium, and of phosphates of lime
and magnesia, are present.

The fatty matter is contained in small cells, and forms the greater part
of the cream which rises to the surface of the milk on standing. Hence
_skimmed_ milk is to be preferred for photographic use.

The second constituent, _caseine_, is an organic principle somewhat
analogous to albumen in composition and properties. Its aqueous solution
however does not, like albumen, _coagulate_ on boiling, unless _an acid_
be present, which probably removes a small portion of alkali with which
the caseine was previously combined. The substance termed "rennet," which
is the dried stomach of the calf, possesses the property of coagulating
caseine, but the exact mode of its action is unknown. Sherry wine is also
employed to curdle milk; but brandy and other spirituous liquids, when
free from acid and astringent matter, have no effect.

In all these cases a proportion of the caseine usually remains in a
soluble form in the _whey_; but when the milk is coagulated by the
addition of acids, the quantity so left is very small, and hence the
use of the rennet is to be preferred, since the presence of caseine
facilitates the reduction of the sensitive silver salts.

Caseine combines with oxide of silver in the same manner as albumen,
forming a white coagulum, which becomes _brick-red_ on exposure to light.

Sugar of milk, the third principal constituent, differs from both
cane and grape sugar; it may be obtained by evaporating _whey_ until
crystallization begins to take place. It is hard and gritty, and only
slightly sweet; slowly soluble, without forming a syrup, in about two and
a half parts of boiling, and six of cold water. It does not ferment and
form alcohol on the addition of yeast, like grape sugar, but by the action
of _decomposing animal matter_ is converted into lactic acid.

When skimmed milk is exposed to the air for some hours it gradually
becomes _sour_, from lactic acid formed in this way; and if then heated to
ebullition, the caseine coagulates very perfectly.


Nitric Acid.

Symbol, NO{5}. Atomic weight, 54.

Nitric acid, or _aqua-fortis_, is prepared by adding sulphuric acid
to nitrate of potash, and distilling the mixture in a retort. Sulphate
of potash and free nitric acid are formed, the latter of which, being
volatile, distils over in combination with one atom of water previously
united with sulphuric acid.

_Properties._--Anhydrous nitric acid is a solid substance, white and
crystalline, but it cannot be prepared except by an expensive and
complicated process.

The concentrated liquid nitric acid contains 1 atom of water, and has a
sp. gr. of about 1·5: if perfectly pure it is colorless, but usually it
has a slight yellow tint, from partial decomposition into peroxide of
nitrogen: it fumes strongly in the air.

The strength of commercial nitric acid is subject to much variation. An
acid of sp. gr. 1·42, containing about 4 atoms of water, is commonly
met with. If the specific gravity is much lower than this (less than
1·36), it will scarcely be adapted for the preparation of peroxyline.
The yellow _nitrous acid_, so called, is a strong nitric acid partially
saturated with the brown vapors of peroxide of nitrogen; it has a high
specific gravity, but this is somewhat deceptive, being caused in part
by the presence of the peroxide. On mixing with sulphuric acid the color
disappears, a compound being formed which has been termed a _sulphate of
nitrous acid_.

_Chemical properties._--Nitric acid is a powerful oxidizing agent; it
dissolves all the common metals, with the exception of gold and platinum.
Animal substances, such as the cuticle, nails, etc., are tinged of a
permanent yellow color, and deeply corroded by a prolonged application.
Nitric acid forms a numerous class of salts, all of which _are soluble
in water_. Hence its presence cannot be determined by any precipitating
re-agent, in the same manner as that of hydrochloric and sulphuric acid.

_Impurities of Commercial Nitric Acid._--These are principally _chlorine_
and _sulphuric acid_; also peroxide of nitrogen, which tinges the acid
yellow, as already described. Chlorine is detected by diluting the acid
with an equal bulk of distilled water, and adding a few drops of nitrate
of silver,--a _milkiness_, which is chloride of silver in suspension,
indicates the presence of chlorine. In testing for sulphuric acid, dilute
the nitric acid as before, and drop in _a single drop_ of solution of
chloride of barium; if sulphuric acid be present, an insoluble precipitate
of sulphate of baryta will be formed.


Nitrous Acid. (_See_ Silver, Nitrate of.)


Nitrate of Potash.

Symbol, KO NO{5}. Atomic weight, 102.

This salt, also termed _nitre_ or _saltpetre_, is an abundant natural
product, found effloresced upon the soil in certain parts of the East
Indies. It is also produced artificially in what are called nitre-beds.

Nitrate of potash is _an anhydrous salt_,--it contains simply nitric acid
and potash, without any water of crystallization; still, in many cases,
a little water is retained mechanically between the interstices of the
crystals, and therefore it is better to dry before use. This may be done
by laying it in a state of fine powder upon blotting-paper, close to a
fire, or upon a heated metallic plate.


Nitrate of Baryta.

Symbol, BaO NO{5}. Atomic weight, 131.

Nitrate of baryta forms octahedral crystals, which are anhydrous. It is
considerably less soluble than the chloride of barium, requiring 12 parts
of cold and 4 of boiling water for solution. It may be substituted for the
nitrate of lead in the preparation of protonitrate of iron.


Nitrate of Lead.

Symbol, PbO NO{5}. Atomic weight, 166.

Nitrate of lead is obtained by dissolving the metal, or the oxide of lead,
in _excess_ of nitric acid, diluted with 2 parts of water. It crystallizes
on evaporation in white anhydrous tetrahedra and octahedra, which are
hard, and decrepitate on being heated; they are soluble in 8 parts of
water at 60°.

Nitrate of lead forms with sulphuric acid, or soluble sulphates, a white
precipitate, which is the insoluble sulphate of lead. The _Iodide_ of lead
is also very sparingly soluble in water.


Nitrate of Silver. (_See_ Silver, Nitrate of.)


Nitro-Hydrochloric Acid.

Symbol, NO{4} + Cl.

This liquid is the aqua-regia of the old alchemists. It is produced by
mixing nitric and hydrochloric acids: the oxygen contained in the former
combines with the hydrogen of the latter, forming water and liberating
chlorine, thus:--

  NO{5} + HCl = NO{4} + HO + Cl.

The presence of free chlorine confers on the mixture the power of
dissolving gold and platinum, which neither of the two acids possesses
separately. In preparing aqua-regia it is usual to mix one part, by
measure, of nitric acid with four of hydrochloric acid, and to dilute
with an equal bulk of water. The application of a gentle heat assists the
solution of the metal; but if the temperature rises to the boiling point,
a violent effervescence and escape of chlorine takes place.


Oxygen.

Symbol, O. Atomic weight, 8.

Oxygen gas may be obtained by heating nitrate of potash to redness, but in
this case it is contaminated with a portion of nitrogen. The salt termed
chlorate of potash (the composition of which is closely analogous to that
of the nitrate, chlorine being substituted for nitrogen) yields abundance
of pure oxygen gas on the application of heat, leaving behind chloride of
potassium.

_Chemical Properties._--Oxygen combines eagerly with many of the chemical
elements, forming oxides. This chemical affinity however is not well
seen when the elementary body is exposed to the action of _oxygen in the
gaseous form_. It is the _nascent_ oxygen which acts most powerfully as
an oxidizer. By nascent oxygen is meant oxygen on the point of separation
from other elementary atoms with which it was previously associated; it
may then be considered to be in the liquid form, and hence it comes more
perfectly into contact with the particles of the body to be oxidized.

Illustrations of the superior chemical energy of nascent oxygen are
numerous, but none perhaps are more striking than the mild and gradual
oxidizing influence exerted by atmospheric air, as compared with the
violent action of nitric acid and bodies of that class which contain
oxygen loosely combined.


Oxymel.

This syrup of honey and vinegar is prepared as follows:--Take of

  Honey                                               1 pound.
  Acid, acetic, fortiss. (Beaufoy's acid)            11 drachms.
  Water                                              13 drachms.

Stand the pot containing the honey in boiling water until a scum rises
to the surface, which is to be removed two or three times. Then add the
acetic acid and water, and skim once more if required. Allow to cool, and
it will be fit for use.


Potash.

Symbol, KO + HO. Atomic weight, 57.

Potash is obtained by separating the carbonic acid from carbonate of
potash by means of caustic lime. Lime is a more feeble base than potash,
but the carbonate of lime, being _insoluble_ in water, is at once formed
on adding milk of lime to a solution of carbonate of potash.

_Properties._--Usually met with in the form of solid lumps, or in
cylindrical sticks, which are formed by melting the potash and running
it into a mould. It always contain some atoms of water, which cannot be
driven off by the application of heat.

Potash is soluble almost to any extent in water, much heat being evolved.
The solution is powerfully alkaline and acts rapidly upon the skin; it
dissolves fatty and resinous bodies, converting them into soaps; Solution
of potash absorbs carbonic acid quickly from the air, and should therefore
be preserved in stoppered bottles; the glass stoppers must be wiped
occasionally, in order to prevent them from becoming immovably fixed by
the solvent action of the potash upon the silica of the glass.

The liquor potassæ of the London Pharmacopoeia has a sp. gr. of 1·063,
and contains about 5 per cent; of real potash. It is usually contaminated
with _carbonate_ of potash, which causes it to effervesce on the addition
of acids; also, to a less extent, with sulphate of potash, chloride of
potassium, silica, etc.


Potash, Carbonate of.

Symbol, KO CO{2}. Atomic weight, 70.

The impure carbonate of potash, termed _pearlash_, is obtained from the
ashes of wood and vegetable matter, in the same manner as carbonate of
soda is prepared from the ashes of seaweeds. Salts of potash and of soda
appear essential to vegetation, and are absorbed and approximated by
the living tissues of the plant. They exist in the vegetable structure
combined with organic acids in the form of salts, like the oxalate,
tartrate, etc., which when burned are converted into carbonates.

_Properties._--The pearlash of commerce contains large and variable
quantities of chloride of potassium, sulphate of potash, etc. A purer
carbonate is sold, which is free from sulphates, and with only a trace of
chlorides. Carbonate of potash is a strongly alkaline salt, deliquescent,
and soluble in twice its weight of cold water; insoluble in alcohol, and
employed to deprive it of water.


Pyrogallic Acid.

Symbol, C{8}H{4}O{4} (Stenhouse). Atomic weight. 84.

The term _pyro_ prefixed to gallic acid implies that the new substance is
obtained by the _action of heat_ upon that body. At a temperature of about
410° Fahr., gallic acid is decomposed, and a white sublimate forms, which
condenses in lamellar Crystals; this is pyrogallic acid.

Pyrogallic acid is very soluble in cold water, and in alcohol and ether;
the solution decomposes and becomes brown by exposure to the air. It gives
an indigo blue color with protosulphate of iron, which changes to dark
green if any persulphate be present.

Although termed an _acid_, this substance is strictly _neutral_; it does
not redden litmus-paper, and forms no salts. The addition of potash
or soda decomposes pyrogallic acid, at the same time increasing the
attraction for oxygen; hence this mixture may conveniently be employed for
absorbing the oxygen contained in atmospheric air. The compounds of silver
and gold are reduced by pyrogallic acid even more rapidly than by gallic
acid, the reducing agent absorbing the oxygen, and becoming converted into
carbonic acid and a brown matter insoluble in water.

Commercial pyrogallic acid is often contaminated with empyreumatic oil,
and also with a black insoluble substance known as _metagallic acid_,
which is formed when the heat is raised above the proper temperature in
the process of manufacture.


Sel D'or. (_See_ Gold, Hyposulphite of.)


Silver.

Symbol, Ag. Atomic Weight, 108.

This metal, the _luna_ or _diana_ of the alchemists, is found native in
Peru and Mexico; it occurs also in the form of sulphuret of silver.

When pure it has a sp. gr. of 10·5, and is very malleable and ductile;
melts at a bright red heat. Silver does not oxidize in the air, but
when exposed to an impure atmosphere containing traces of sulphuretted
hydrogen, it is slowly tarnished from formation of sulphuret of silver. It
dissolves in sulphuric acid, but the best solvent is nitric acid.

The standard coin of the realm is an alloy of silver and copper,
containing about one-eleventh of the latter metal. It may be converted
into nitrate of silver, sufficiently pure for photographic purposes,
by dissolving it in nitric acid and evaporating the solution to the
crystallizing point: or, if the quantity be small, the solution may be
boiled down to complete dryness, and the residue _fused_ strongly; which
decomposes the nitrate of copper, but leaves the greater portion of the
silver salt unaffected. (N. B. Nitrate of silver which has undergone
fusion contains nitrite of silver, and will require the addition of acetic
acid if used for preparing the collodion sensitive film.)


Silver, Ammonio-Nitrate of.

Crystallized nitrate of silver absorbs ammoniacal gas rapidly, with
production of heat sufficient to fuse the resulting compound, which
is white, and consists of 100 parts of the nitrate + 29·5 of ammonia.
The compound however which photographers employ under the name of
ammonio-nitrate of silver, may be viewed more simply as a solution of the
oxide of silver in ammonia, without reference to the nitrate of ammonia
necessarily produced in the reaction.

Very strong ammonia, in acting upon oxide of silver, converts it into
a black powder, termed _fulminating silver_, which possesses the most
dangerous explosive properties. Its composition is uncertain. In
preparing ammonio-nitrate of silver by the common process, the oxide
first precipitated occasionally leaves a little black powder behind, on
re-solution; this does not appear, however, according to the observations
of the author, to be fulminating silver.

In sensitizing salted paper by the ammonio-nitrate of silver, _free
ammonia_ is necessarily formed. Thus:--

  Chloride of ammonium + oxide of silver in ammonia
    = chloride of silver + ammonia + water.


Silver, Oxide of.

Symbol, AgO. Atomic weight, 116.

If a little potash or ammonia be added to solution of nitrate of silver,
a brown substance is formed, which, on standing, collects at the bottom
of the vessel. This is oxide of silver, displaced from its previous
state of combination with nitric acid by the stronger oxide, potash.
Oxide of silver is soluble _to a very minute extent_ in pure water, the
solution possessing an alkaline reaction to litmus; it is easily dissolved
by nitric or acetic acid, forming a neutral nitrate or acetate; also
soluble in ammonia (ammonio-nitrate of silver), and in nitrate of ammonia
hyposulphite of soda, and cyanide of potassium. Long exposure to light
converts it into a black substance, which is probably a suboxide.

_Properties of the Suboxide of Silver._--Suboxide of silver bears the same
relation to the ordinary brown protoxide of silver that subchloride bears
to protochloride of silver.

It is a black powder, which assumes the metallic lustre on rubbing, and
when treated with dilute acids is resolved into protoxide of silver which
dissolves, and metallic silver.


Silver, Chloride of.

Symbol, AgCl. Atomic weight, 144.

_Preparation of Chloride of Silver by double decomposition._--In order
to illustrate this, take a solution in water of chloride of sodium or
"common salt," and mix it with a solution containing nitrate of silver;
immediately a dense, curdy, white precipitate falls, which is the
substance in question.

In this reaction the elements change places; the chlorine leaves the
sodium with which it was previously combined, and crosses over to the
silver; the oxygen and nitric acid are released from the silver, and unite
with the sodium: thus

  Chloride of sodium + nitrate of silver
    = Chloride of silver + nitrate of soda.

This interchange of elements is termed by chemists _double decomposition_.

The essential requirements in two salts intended for the preparation of
chloride of silver, are simply that the first should contain chlorine,
the second silver, and that both should be soluble in water; hence the
chloride of potassium or ammonium may be substituted for the chloride of
sodium, and the sulphate or acetate for the nitrate of silver.

In preparing chloride of silver by double decomposition, the white clotty
masses which first form must be washed repeatedly with water, in order to
free them from soluble nitrate of soda, the other product of the change.
When this is done, the salt is in a pure state, and may be dried, etc., in
the usual way.

_Properties of Chloride of Silver._--Chloride of silver differs in
appearance from the nitrate of silver. It is not met with in crystals,
but forms a soft white powder resembling common chalk or whiting. It is
tasteless and insoluble in water; unaffected by boiling with the strongest
nitric acid, but sparingly dissolved by concentrated hydrochloric acid.

Ammonia dissolves chloride of silver freely, as do solutions of
hyposulphite of soda and cyanide of potassium. Concentrated solutions
of alkaline chlorides, iodides, and bromides are likewise solvents of
chloride of silver, but to a limited extent.

Dry chloride of silver heated to redness fuses, and concretes on cooling
into a tough and semi-transparent substance, which has been termed _horn
silver_ or _luna cornea_.

Placed in contact with metallic zinc or iron acidified with dilute
sulphuric acid, chloride of silver is reduced to the metallic state, the
chlorine passing to the other metal under the decomposing influence of the
galvanic current which is established.

_Preparation and properties of the Subchloride of Silver._--If a plate
of polished silver be dipped in solution of perchloride of iron, or of
bichloride of mercury, a _black stain_ is produced, the iron or mercury
salt losing a portion of chlorine, which passes to the silver and
converts it superficially into subchloride of silver. This compound
differs from the white chloride of silver in containing less chlorine
and more of the metallic element; the composition of the latter being
represented by the formula AgCl, that of the former may perhaps be written
as Ag{2}Cl. (?)

Subchloride of silver is interesting to the photographer as corresponding
in properties and composition with the ordinary chloride of silver
blackened by light. It is a pulverulent substance of a bluish-black color,
which is decomposed by ammonia, hyposulphite of soda, and cyanide of
potassium, into chloride of silver which dissolves, and insoluble metallic
silver.


Silver, Bromide of.

Symbol, AgBr. Atomic weight, 186.

This substance so closely resembles the corresponding salts containing,
chlorine and iodine, that a short notice of it will suffice.

Bromide of silver is prepared by exposing a silvered plate to the vapor
of bromine, or by adding solution of bromide of potassium to nitrate
of silver. It is an insoluble substance, slightly yellow in color, and
distinguished from iodide of silver by dissolving in strong ammonia and in
chloride of ammonium. It is freely soluble in hyposulphite of soda and in
cyanide of potassium.


Silver, Citrate of. (_See_ Citric Acid.)


Silver, Iodide of.

Symbol, AgI. Atomic weight, 234.

_Preparation and Properties of Iodide of Silver._--Iodide of silver may be
formed in an analogous manner to the chloride, viz. by the direct action
of the vapor of iodine upon metallic silver, or by double decomposition
between solutions of iodide of potassium and nitrate of silver.

When prepared by the latter mode it forms an impalpable powder, the color
of which varies slightly with the manner of precipitation. If the iodide
of potassium be in excess, the iodide of silver falls to the bottom of the
vessel nearly white; but with an excess of nitrate of silver it is of a
straw-yellow tint. This point may be noticed, because the yellow salt is
the one adapted for photographic use, the other being insensible to the
influence of light.

Iodide of silver is tasteless and inodorous; insoluble in water and in
dilute nitric acid. It is scarcely dissolved by ammonia, which serves
to distinguish it from the chloride of silver, freely soluble in that
liquid. Hyposulphite of soda and cyanide of potassium both dissolve iodide
of silver; it is also soluble in solutions of the alkaline bromides and
iodides.


Silver, Fluoride of.

Symbol, AgF. Atomic weight, 127.

This compound differs from those just described in being soluble in
water. The dry salt fuses on being heated, and is reduced by a higher
temperature, or by exposure to light.


Silver, Sulphuret of.

Symbol, AgS. Atomic weight, 124.

This compound is formed by the action of sulphur upon metallic silver, or
of sulphuretted hydrogen, or hydrosulphate of ammonia, upon the silver
salts; the decomposition of hyposulphite of silver also furnishes the
black sulphuret.

Sulphuret of silver is insoluble in water, and nearly so in those
substances which dissolve the chloride, bromide, and iodide, such as
ammonia, hyposulphites, cyanides, etc.; but it dissolves in nitric acid,
being converted into soluble sulphate and nitrate of silver.


Silver, Nitrate of.

Symbol, AgO NO{5}. Atomic weight, 170.

Nitrate of silver is prepared by dissolving metallic silver in nitric
acid. Nitric acid is a powerfully acid and corrosive substance, containing
two elementary bodies united in definite proportions. These are nitrogen
and oxygen; the latter being present in greatest quantity.

Nitric acid is a powerful solvent for the metallic bodies generally. To
illustrate its action in that particular, as contrasted with other acids,
place pieces of silver foil in two test-tubes, the one containing dilute
sulphuric, the other dilute nitric acid; on the application of heat a
violent action soon commences in the latter, but the former is unaffected.
In order to understand the cause of the difference, it must be borne in
mind that when a metallic substance dissolves in an acid, the nature of
the solution is unlike that of an _aqueous_ solution of salt or sugar.
If you take salt water, and boil it down until the whole of the water
has evaporated, you obtain the salt again, with properties the same as
at first; but if a similar experiment be made with a solution of silver
in nitric acid, the result is different: in that case you do not get
metallic silver on evaporation, but silver _combined with oxygen_ and
_nitric acid_, both of which are tightly retained, being, in fact, in a
state of chemical combination with the metal.

If we closely examine the effects produced by treating silver with nitric
acid, we find them to be of the following nature:--first, a certain
amount of oxygen is imparted to the metal, so as to form an _oxide_, and
afterwards this oxide dissolves in another portion of the nitric acid,
producing _nitrate_ of the oxide, or, as it is shortly termed, nitrate of
silver.

It is therefore the _instability_ of nitric acid, its proneness to part
with oxygen, which renders it superior to sulphuric acid in the experiment
of dissolving silver. Nitric acid stands high in the list of "oxidizing
agents," and it is important that the photographer should bear this fact
in mind.

_Properties of Nitrate of Silver._--In the preparation of nitrate of
silver, when the metal has dissolved, the solution is boiled down in order
to drive off the excess of nitric acid, and set aside to crystallize. The
salt, however, as so obtained is still acid to test-paper, and requires
either recrystallization, or a careful heating to about 300° Fahrenheit,
to render it perfectly neutral.

Pure nitrate of silver occurs in the form of white crystalline plates,
which are very heavy and dissolve readily in an equal weight of cold
water. The solubility is much lessened by the presence of free nitric
acid, and in the _concentrated_ nitric acid the crystals are almost
insoluble. Boiling alcohol takes up about one-fourth part of its weight
of the crystallized nitrate, but deposits nearly the whole on cooling.
Nitrate of silver has an intensely bitter and nauseous taste; acting as a
caustic, and corroding the skin by a prolonged application. Its aqueous
solution is perfectly neutral to test-paper.

Heated in a crucible the salt melts, and when poured into a mould and
solidified, forms the _lunar caustic_ of commerce. At a still higher
temperature it is decomposed, and bubbles of oxygen gas are evolved.
The melted mass, cooled and dissolved in water, leaves behind a black
powder, and yields a solution which is faintly alkaline to test-paper. The
alkalinity depends upon the presence of _nitrite_ of silver associated
with excess of oxide, in the form probably of a basic or _sub_-nitrite of
silver.[B]

[Footnote B: Nitrite of silver differs from the nitrate in containing less
oxygen, and is formed from it by the abstraction of two atoms of that
element.]

Solution of nitrate of silver is decomposed by iron, zinc, copper,
mercury, etc., the nitric acid and oxygen passing to the other metal, and
metallic silver being precipitated.


Silver, Nitrite of.

Symbol, AgO NO{3}. Atomic weight, 154.

Nitrite of silver is a compound of nitrous acid, or NO{3}, with oxide of
silver. It is formed by heating nitrate of silver, so as to drive off a
portion of its oxygen, or more conveniently, by mixing nitrate of silver
and nitrate of potash in equal parts, fusing strongly, and dissolving in a
small quantity of boiling water; on cooling, the nitrite crystallizes out,
and may be purified by pressing in blotting paper. Mr. Hadow describes
an economical method of preparing nitrite of silver in quantity, viz. by
heating 1 part of starch in 8 of nitric acid of 1·25 specific gravity,
and conducting the evolved gases into a solution of pure carbonate of
soda until effervescence has ceased. The nitrite of soda thus formed is
afterwards added to nitrate of silver in the usual way.

_Properties._--Nitrite of silver is soluble in 120 parts of cold water;
easily soluble in boiling water, and crystallizes, on cooling, in long
slender needles. It has a certain degree of affinity for oxygen, and tends
to pass into the condition of nitrate of silver; but it is probable that
its photographic properties depend more upon a decomposition of the salt
and liberation of nitrous acid.

_Properties of Nitrous Acid._--This substance possesses very feeble
acid properties, its salts being decomposed even by acetic acid. It is
an unstable body, and splits up, in contact with water, into binoxide
of nitrogen and nitric acid. The peroxide of nitrogen, NO{4}, is also
decomposed by water and yields the same products.


Silver, Acetate of.

Symbol, AgO (C{4}H{3}O{3}). Atomic weight, 167.

This is a difficultly soluble salt, deposited in lamellar crystals when
an acetate is added to a strong solution of nitrate of silver. If _acetic
acid_ be used in place of an acetate, the acetate of silver does not fall
so readily, since the nitric acid which would then be liberated impedes
the decomposition.


Silver, Hyposulphite of.

Symbol, AgO S{2}O{3} . Atomic weight, 164.

In order to understand, more fully how _decomposition_ of hyposulphite
of silver may affect the process of fixing, the peculiar properties
of this salt should be studied. With this view nitrate of silver and
hyposulphite of soda may be mixed in equivalent proportions, viz. about
twenty-one grains of the former salt to sixteen grains of the latter,
first dissolving each in separate vessels in half an ounce of distilled
water. These solutions are to be added to each other and well agitated;
immediately a dense deposit forms, which is hyposulphite of silver.

At this point a curious series of changes commences. The precipitate, at
first white and curdy, soon alters in color: it becomes canary-yellow,
then of a rich orange-yellow, afterwards liver-color, and finally black.
The _rationale_ of these changes is explained to a certain extent by
studying the composition of the hyposulphite of silver.

The formula for this substance is as follows:--

  AgO S{2}O{2},

But AgO S{2}O{2} plainly equals AgS, or sulphuret of silver, and SO{3}, or
sulphuric acid. The acid reaction assumed by the supernatant liquid is due
therefore to sulphuric acid, and the black substance formed is sulphuret
of silver. The yellow and orange-yellow compounds are earlier stages of
the decomposition, but their exact nature is uncertain.

The instability of hyposulphite of silver is principally seen when, it is
in an isolated state: the presence of an excess of hyposulphite of soda
renders it more permanent, by forming a double salt.

In fixing photographic prints this brown deposit of sulphuret of silver
is very liable to form in the bath and upon the picture; particularly
so when the _temperature_ is high. To obviate it observe the following
directions:--It is especially in the reaction between _nitrate of silver_
and hyposulphite of soda that the blackening is seen; the chloride and
other _insoluble_ salts of silver being dissolved, even to saturation,
without any decomposition of the hyposulphite first formed. Hence, if the
print be washed in water to remove the soluble nitrate, a very much weaker
fixing bath than usual may be employed. This plan, however, involving a
little additional trouble, is, on that account, often objected to, and,
when such is the case, a _concentrated_ solution of hyposulphite of soda
must be used, in order to dissolve off the white hyposulphite of silver
before it begins to decompose. When the proofs are taken at once from
the printing frame and immersed in a _dilute_ bath of hyposulphite (one
part of the salt to six or eight of water), _a shade of brown_ may often
be observed to pass over the surface of the print, and a large deposit
of sulphuret of silver soon forms as the result of this decomposition.
On the other hand, with a strong hyposulphite bath there is little or no
discoloration and the black deposit is absent.

But even if, by a preliminary removal of the nitrate of silver, the danger
of blackening be in a great measure obviated, yet the print must not be
taken out of the fixing bath too speedily, or some appearance of brown
patches, visible by transmitted light, may occur.

Each atom of nitrate of silver requires _three_ atoms of hyposulphite of
soda to form the _sweet and soluble double salt_, and hence, if the action
be not continued sufficiently long, another compound will be formed almost
tasteless and insoluble. Even immersion in a new bath of hyposulphite of
soda does not fix the print when once the yellow stage of decomposition
has been established. This yellow salt is insoluble in hyposulphite of
soda, and consequently remains in the paper.


Sugar of Milk. (_See_ Milk.)


Sulphuretted Hydrogen. (_See_ Hydrosulphuric Acid.)


Sulphuric Acid.

Symbol, SO{3}. Atomic weight, 40.

Sulphuric acid maybe formed by oxidizing sulphur with boiling nitric
acid; but this plan would be too expensive to be adopted on a large
scale. The commercial process for the manufacture of sulphuric acid is
exceedingly ingenious and beautiful, but it involves reactions which are
too complicated to admit of a superficial explanation. The sulphur is
first burnt into gaseous sulphurous acid (SO{2}), and then, by the agency
of binoxide of nitrogen gas, an additional atom of oxygen is imparted from
the atmosphere, so as to convert the SO{2} into SO{3}, or sulphuric acid.

_Properties._--Anhydrous sulphuric acid is a white crystalline solid. The
strongest liquid acid always contains one atom of water, which is closely
associated with it, and cannot be driven off by the application of heat.

This _mono-hydrated_ sulphuric acid, represented by the formula HO SO{3},
is a dense fluid, having a specific gravity of about 1·845; boils at
620°, and distils without decomposition. It is not volatile at common
temperatures, and therefore does not _fume_ in the same manner as nitric
or hydrochloric acid. The concentrated acid may be cooled down even to
zero without solidifying; but a weaker compound, containing twice the
quantity of water, and termed _glacial_ sulphuric acid, crystallizes at
40° Fahr. Sulphuric acid is intensely acid and caustic, but it does not
destroy the skin or dissolve metals so readily as nitric acid. It has an
energetic attraction for water, and when the two are mixed, condensation
ensues, and much heat is evolved; four parts of acid and one of water
produce a temperature equal to that of boiling water. Mixed with aqueous
nitric acid, it forms the compound known as nitro-sulphuric acid.

Sulphuric acid possesses intense chemical powers, and displaces the
greater number of ordinary acids from their salts. It _chars_ organic
substances, by removing the elements of water, and converts alcohol into
ether in a similar manner. The _strength_ of a given sample of sulphuric
acid may generally be calculated from its specific gravity, and a table is
given by Dr. Ure for that purpose.

_Impurities of Commercial Sulphuric Acid._--The liquid acid sold as _oil
of vitriol_ is tolerably constant in composition, and seems to be as well
adapted for photographic use as the _pure_ sulphuric acid, which is far
more expensive. The specific gravity should be about 1·836 at 60°. If
a drop, evaporated upon platinum foil, gives a fixed residue, probably
bisulphate of potash is present. A milkiness, on dilution, indicates
sulphate of lead.

_Test for Sulphuric Acid._--If the presence of sulphuric acid, or a
soluble sulphate, be suspected in any liquid, it is tested for by adding a
few drops of dilute solution of chloride of barium, or nitrate of baryta.
A white precipitate, _insoluble in nitric acid_, indicates sulphuric acid.
If the liquid to be tested is very acid, from nitric or hydrochloric acid,
it must be largely diluted before testing, or a crystalline precipitate
will form, caused by the sparing solubility of the chloride of barium
itself in acid solutions.


Sulphurous Acid.

Symbol, SO{2}. Atomic weight, 32.

This is a gaseous compound, formed by burning sulphur in atmospheric air
or oxygen gas; also by heating oil of vitriol in contact with metallic
copper, or with charcoal.

When an acid of any kind is added to hyposulphite of soda, sulphurous acid
is formed as a product of the decomposition of hyposulphurous acid, but it
afterwards disappears from the liquid by a secondary reaction, resulting
in the production of trithionate and tetrathionate of soda.

_Properties._--Sulphurous acid possesses a peculiar and suffocating odor,
familiar to all in the fumes of burning sulphur. It is a feeble acid, and
escapes with effervescence, like carbonic acid, when its salts are treated
with oil of vitriol. It is soluble in water.


_Water._

Symbol, H{2}O. Atomic weight, 9.

Water is an oxide of hydrogen, containing single atoms of each of the
gases.

_Distilled water_ is water which has been vaporized and again condensed:
by this means it is freed from earthy and saline impurities, which, not
being volatile, are left in the body of the retort. _Pure_ distilled water
leaves no residue on evaporation, and should remain perfectly clear on the
addition of nitrate of silver, _even when exposed to the light_; it should
also be neutral to test-paper.

The condensed water of steam-boilers sold as distilled water is apt to be
contaminated with oily and empyreumatic matter, which discolors nitrate of
silver, and is therefore injurious.

_Rain-water_, having undergone a natural process of distillation, is
free from inorganic salts, but it usually contains a minute portion of
_ammonia_, which gives it an alkaline reaction to test-paper. It is very
good for photographic purposes if collected in clean vessels, but when
taken from a common rain-water tank should always be examined, and if much
organic matter be present, tinging it of a brown color and imparting an
unpleasant smell, it must be rejected.

_Spring_ or _river_ water, commonly known as "hard water," usually
contains sulphate of lime, and carbonate of lime dissolved in carbonic
acid: also chloride of sodium in greater or less quantity. On boiling
the water, the carbonic acid gas is evolved, and the greater part of
the carbonate of lime (if any is present) deposits, forming an earthy
incrustation on the boiler.

In testing water for sulphates and chlorides, acidify a portion with a few
drops of _pure_ nitric acid, free from chlorine (if this is not at hand,
use pure acetic acid); then divide it into two parts, and add to the first
a _dilute_ solution of chloride of barium, and to the second nitrate of
silver,--a milkiness indicates the presence of sulphates in the first case
or of chlorides in the second. The _photographic nitrate bath_ cannot be
used as a test, since the iodide of silver it contains is precipitated
on dilution, giving a milkiness which might be mistaken for chloride of
silver.

Common hard water can often be used for making a nitrate bath when nothing
better is at hand. The chlorides it contains are precipitated by the
nitrate of silver, leaving soluble _nitrates_ in solution, which are not
injurious. The carbonate of lime, if any is present, neutralizes free
nitric acid, rendering the bath alkaline in the same manner as carbonate
of soda. Sulphate of lime, usually present in well water, is said to
exercise a retarding action upon the sensitive silver salts, but on this
point the writer is unable to give certain information.

Hard water is not often sufficiently pure for the developing fluids. The
chloride of sodium it contains decomposes the nitrate of silver upon the
film, and the image cannot be brought out perfectly. The New River water,
however supplied to many parts of London, is almost free from chlorides
and answers very well. In other cases a few drops of nitrate of silver
solution may be added to separate the chlorine, taking care not to use a
large excess.


Black Varnish.

_Asphaltum, dissolved in Spirits or Oil of Turpentine._--The asphaltum may
be coarsely pulverized and put into a bottle containing the turpentine,
and in a few hours, if it be occasionally shaken, it will be dissolved and
ready for use. It should be of about the consistency of thick paste.

I use the above, but will now give two more compositions, for any who may
wish to adopt them:

_Black Japan._--Boil together a gallon of boiled linseed oil, 8 ounces of
amber, and 3 ounces of asphaltum. When sufficiently cool, thin it with oil
of turpentine.

_Brunswick Black._--Melt 4 lbs. of asphaltum, add 2 lbs. of hot boiled
linseed oil, and when sufficiently cool, add a gallon of oil of turpentine.

The following is from _Humphrey's Journal_, Vol. viii, number 16.

_Black Varnish._--I generally purchase this from the dealer; but I have
made an article which answered the purpose well, by dissolving pulverized
asphaltum in spirits of turpentine. Any of the black varnishes can be
improved by the addition of a little bees'-wax to it. It is less liable to
crack and gives an improved gloss.

Before closing this chapter, it has been thought advisable to remark,
that one of the most important departments of Photography is the practice
of its chemistry. Many of the annoying failures experienced by those who
are just engaging in the practice of the art, arise from the want of good
and pure chemical agents, and the most certain way to avoid this, is
to purchase them only from persons who thoroughly understand both their
nature and mode of application. As many who may read this work might wish
to know the prices of the various articles employed in the practice of the
processes given, they can be informed by addressing the author, who will
furnish them with a printed Price List.



                            PRACTICAL DETAILS

                                  OF THE

                                 POSITIVE

                                    OR

                           =AMBROTYPE PROCESS.=



CHAPTER IV.

LEWIS'S PATENT VICES FOR HOLDING THE GLASS--CLEANING AND DRYING
THE GLASS--COATING--EXPOSURE IN THE CAMERA--DEVELOPING--FIXING OR
BRIGHTENING--BACKING UP, &C.


Manipulations.

[Sidenote: MANIPULATIONS.]

Under the head of manipulations I give the method I employ, and avoid
confusion by omitting all comments upon the thousand suggestions of others.

The glass is to have its sharp edges and corners removed, by drawing a
file once or twice over it. The article used for holding the glass is
called a vice. This vice is firmly secured to a bench.

[Since the foregoing pages have been in type there has been introduced
into market a new patent vice, adopted both for glass and plate blocks. I
find it, although a little more expensive, an article better suited to the
wants of the operator or amateur. It is called Lewis's Patent Glass Vice.]

Clasp the glass firmly in the vice, and pour or _spurt_ upon it a little
alcohol and rotten stone, previously formed into a paste, and then, with
a piece of cotton flannel, the same as used in the daguerreotype, rub the
glass until it is perfectly cleansed from all foreign substances, which
will soon be known by experience. The rotten stone paste should not be
allowed to dry while rubbing, as it is more liable to scratch the glass. I
use another small bottle containing clear alcohol, which I spurt upon the
glass, to obviate the drying.

When the glass has been sufficiently cleaned, it should, while wet, be put
in a vessel of water for future rinsing. Clean, as before, as many plates
of glass as may be required, and when enough are ready, rinse them off in
the water, and then in a quantity of clean water, or a running current,
give them a second thorough rinsing, and set them aside to drain.

A convenient method of doing this, is to drive two nails horizontally
into the wall or partition, a sufficient distance apart (say about 2-1/2
inches) for the glass to rest on: the upper corner of the glass should
be placed against the wall, and the extreme lower diagonal corner left
hanging between the nails--which will probably be found the best position
for draining yet suggested.

After drying, they may be put into a box for safe and clean keeping.
Particular caution is necessary to avoid handling the glass during the
operation. I never take the glass between my fingers, so that they come in
contact with _both sides_ of it, except at one particular corner, as at
Figs. A and B. A quantity of glass prepared as above, may be kept on hand
for use two or three days, and when wanted they should be again put into
the vice[C] and cleaned, first with cotton flannel wet with alcohol, and
then with dry flannel; and then, at a temperature slightly above that of
the surrounding atmosphere, except in cases where the thermometer stands
above 70°, it is ready for the brush,[D] which should be carefully applied
to each surface, to free it from all particles of dust, and then it is
ready for the film of collodion.

[Footnote C: The vice should be thoroughly cleansed, and no particles of
rotten stone, or other matter, be allowed to come in contact with the
glass, as it might adhere to the edges and wash off into the silvering
bath, and ultimately cause specks. Always remember that cleanliness is an
indispensable requisite in order to produce a good picture.]

[Footnote D: One of the most desirable articles I have found for this
purpose is the wide (3 inch) flat camel's-hair brush often called a
blender.]

[Illustration: Fig. A. Fig. B.]

The glass is held between the thumb and forefinger of the left hand by the
corner 1, Fig. A., 3 and 4 towards and nearest the body, and as nearly
level as possible. I find this the best position to hold the glass; as, in
the case of the larger ones, they can be rested on the end of the little
finger, which should be placed as near the edge as possible. Then, from
the collodion vial, pour on the collodion, commencing a little beyond
the centre and towards 1, continuing pouring in the same place until the
collodion nearly reaches the thumb--the glass slightly inclined that way;
then let the glass incline towards 4, and continue to pour towards 2.

As soon as enough has been put on to liberally flow the glass, rapidly and
steadily raise corner 1, and hold it directly over 3, where the excess
will flow oil into the mouth of the vial, which should be placed there to
receive it. In case of a speck of dust falling at the time of coating, it
can often be prevented from injuring the surface by changing the direction
of the flowing collodion, so as to stop it in some place where it will
not be seen when the picture is finished. Now, with the thumb and finger
of the right hand, I wipe off any drops or lines of collodion that may be
found upon the _outer_ edge or side of the glass, being careful not to
disturb that connected with the face.

When the coating has become sufficiently dry, so that when I put my finger
against it, it does not break the film, but only leaves a print, I put
it into the silvering bath [_see_ Fig. p. 34]. I generally try corners 2
and 3. The time, from the first commencement of pouring on collodion to
its being put into the bath, should not exceed about half a minute, at a
temperature of 60°. The finger test is the best I have found. The glass
is to be rested on a dipper [_see_ Fig. p. 34], and placed steadily and
firmly into the nitrate of silver bath--this in a dark room. It should not
be allowed to rest for an instant as it is entering the solution, or it
would cause a line. The time for the glass to remain in the bath depends
upon the age and amount of silver the bath contains; for a new solution,
from _two_ to _three_ minutes will be sufficient to give the proper
action. If it be old, three to five minutes will be better. When it is
properly coated, it can be raised up and taken by the corner, and allowed
to drain for a few seconds, and then should be placed in the tablet, and
is ready for the camera. The time of exposure will depend upon the amount
of light present. If the bath is newly mixed, and the collodion recently
iodized, it should produce a sufficiently strong impression by an exposure
of about one-third of the time required for a daguerreotype. If the
collodion has been iodized some time, and the bath is old, about one-half
of the time necessary to produce a daguerreian image will be required.

The plate should in no case be allowed to become dry from the time it
is taken from the bath up to the time of pouring on the developer. At a
temperature of about 70°, I have had the glass out of the bath ten minutes
without drying. After exposure, the glass should be taken again into the
dark room, and removed from the tablet and held over a sink, pail, or
basin and the developing solution poured on it as follows: hold the glass
between the thumb and finger of the left hand, by the opposite end corner
from that in coating with collodion, _i. e._, 2, and let 3 and 4 be from
you.

[Sidenote: MANIPULATIONS OF THE POSITIVE PROCESS.]

Commence pouring on the developing solution at the end by the thumb, and
let it flow quickly and evenly over the entire surface, the first flooding
washing off any excess of nitrate of silver there may be about the edges
or corners of the glass (if this silver is not washed off, it flows over
the edges and on the surface of the impression, producing white wavy
clouds of scum), and then hold the glass as nearly level as possible,
it having upon its surface a thin covering of solution (care should be
observed not to pour the developing solution on the plate in _one place_,
as it would remove all the nitrate of silver and prevent the development
of the image, leaving only a dark or black spot where it is poured on).
Put down the bottle containing the developing solution, and take up a
quart pitcher previously filled with water, and as soon as the outline of
the image can be plainly seen by the weak or subdued light of an oil or
fluid lamp or candle, pour the water over copiously and rapidly. Continue
this until all the iron solution has been removed. If this is not done,
the plate will be covered with blue scum on the application of the washing
solution. Then the glass can be taken into a light room, and the iodide
of silver coating washed off with the cyanide solution, and then rinsed
with clear pure water, and stood in a position to drain and dry. I place
a little blotting paper under them: it aids in absorbing the water, and
facilitates the operation.

Place the face of the glass against the wall, in order to prevent dust
from falling upon it. I have often dried the coating by holding or
standing the glass adjacent to a stove. A steady heat is advisable, as it
leaves the surface in a more perfect state, and free from any scum. After
the coating is perfectly dry, it is ready for the preserving process. It
should be warmed evenly, and when about milk warm, "Humphrey's Collodion
Gilding" is poured on the image in precisely the same manner as the
collodion. In a few seconds the coating sets, and after three-quarters
of a minute, if it has not become dry, the blaze of a spirit lamp
may be applied to the back and it will immediately become _perfectly
transparent_, and nearly as hard as the glass itself: the effect is
fully equal, if not superior, to that of chloride of gold in gilding the
daguerreotype image. The surface becomes brilliant and permanent. The back
of the glass can now be wiped and cleaned with paper or cloth, and gently
warmed, and then with a common small brush one coat of black varnish can
be applied. This brush should be drawn from side to side across the
glass, and on the side opposite to that which has received the image.

This is in order not to make streaks in the coating of varnish, but to
have uniform lines across the entire length or breadth of the glass. If
the varnish is of the proper consistency, it will flow into a smooth,
even coating. After this first coating is dry, apply a second in the same
manner, only in an opposite direction, so as to cross the lines of the
first, uniting at right angles; when this last coating is very nearly dry,
a piece of paper, glazed black on one side, and cut to the proper size,
can be put next the varnish; it gives it a clean finish, at the same time
that it aids towards a dense blackening.

I sometimes apply the black varnish by flowing, in the same manner as in
putting on the collodion.

This picture is to be colored and put up in the same manner as the
daguerreotype image, with a mat and glass. The last glass may be dispensed
with by first using the collodion gilding, and then upon its surface apply
the black varnish, as before. In this case the image is seen through the
same glass it is on, and without being reversed: in this case the mat goes
on the outside of the glass.

When the image is seen through the glass upon which it is taken, it
cannot be colored with very great success, as it cannot be seen through
the reduced silver forming it. This forms a more or less opaque surface;
but in point of economy the single glass is preferable. Yet I would not
recommend such economy, for I consider that a good impression ought to
be well put up, and the welfare of the art fully substantiates that
consideration.

Many ways have been devised for putting up pictures I have produced
pleasing effects upon colored glasses: for instance, a picture on a light
purple glass has a very pleasing effect; also in some other colors. I have
also used patent leather for backing the image.

I have produced curious and interesting results by placing a piece of
white paper, or coloring white the back of the _whites_ of the image,
and then blackening over or around this. By this means the whites are
preserved very clear.

_Positives for Pins, Lockets, etc._--I employ mica for floating the
collodion on, as it can be as easily cut and fitted as the metallic plate
in the daguerreotype; and positives taken upon fine, clear, transparent
mica, are fully equal to those taken upon glass, and yet they are
ambrotypes.

Mica is an article familiar to every one, as being used in stoves,
gratings, etc.

The method of using it, is to take the impression on a thick piece, and
then split it off, which can readily be done in the most perfect, thin,
transparent plates; it is equally as thin as tissue paper, and can be cut
as easily. The thickness of the piece upon which the impression is taken
is of no moment, since it can be reduced at pleasure and is more easily
handled while thick.


Observations on the Positive Collodion Process.

Fogging.--There are numerous causes which will produce fogging: the
principal ones will be mentioned. One is the admission of light upon the
collodion. This maybe from a want of closeness of the dark room, the
tablet,[E] the camera, or by accidental exposure. The method to locate
the particular cause is to, _first_, when the glass is taken from the
nitrate bath, let it stand for sufficient time to drain, then pour on the
developer, and if the coating assumes a mistiness, or light-grey color,
the fault is in the dark room; again, if the plate, after it has been
treated with the developer and fixed, is clear, then also the fault is
there. Now try the tablet in the same manner, and if not there, try the
camera, and the proper location will be found.

[Footnote E: Since the foregoing pages have been in type an entirely new
feature in the line of apparatus has been introduced; this is W. & W.
H. Lewis's Patent Plate-holder with solid glass corners. These Holders
have every requisite for excluding the light from the sensitive surface;
they are accompanied with a "shut off," so that when the slide is drawn
no light can reach the glass. This, in connection with the unequalled
advantage of the solid corners, makes them the most desirable article for
the Operator. _Humphrey's Journal_, in referring to these Holders, says:--

    "We are always glad to note every step which our mechanics make
    towards improvement on the apparatus used by our practical
    photographic operators, and make the present announcement of one
    which has only to be known to be readily understood, and to be seen
    to be appreciated. A patent has recently been granted for making
    solid glass corners, which are to be attached to plate-holders,
    and form the most perfect article that has ever been introduced.
    Heretofore the operator has had the corners of his plate-holders
    made with separate pieces of glass, cut so as to fit the corners of
    his frames; these are only glued or grooved in, and are constantly
    coming apart, falling out, and annoying in many ways; for our part,
    we never have considered them as fit for use in any manner. We look
    upon the present improvement as destined to entirely supersede all
    the methods heretofore introduced. In this case the collodionized
    or albumenized plate can come in contact with no other substance
    than a single piece of glass, and consequently there is far less
    liability of accident from either the staining of the plate or
    breaking of the holder. The rapid favor this improvement has gained
    already shows its great advantage over all other methods heretofore
    employed."

]

"Decomposition by exposure to light or by long keeping, even in the dark.
The author conceives that it is possible for organic matter alone to
produce, after a time, a partial decomposition of solution of nitrate of
silver, sufficient to prevent it from being employed chemically neutral,
but probably not much interfering with its properties in other respects.

"Use of rain water or of water containing carbonate of silver being
perfectly neutral and from nitric acid. This difficulty is not a
theoretical one only, but has actually been experienced. Rain water
usually contains ammonia, and has a faint alkaline reaction. Pump water
often abounds with carbonate of lime, much of which, but not the whole, is
deposited on boiling. To remove the alkaline condition, add acetic acid,
one drop to half a pint of the solution.

"Partial decomposition of the bath, by contact with metallic iron,
with hyposulphite of soda, or with any developing agent, even in small
quantity. Also by the use of accelerators, which injure the bath by
degrees, and eventually prevent its employment in an accurately neutral
state.

"Vapor of ammonia, or hydrosulphate of ammonia, escaping into the
developing room."

Spots.--One principal cause of spots is _dust_. The operating room
should be kept as free from this as possible, and instead of its being
dusted, it should be wiped with a damp cloth. Specks or flakes of iodide
of silver are often found in the nitrate bath. These sometimes occur by
an ever-iodized collodion, and sometimes by collodion falling off while
being silvered. When this occurs, the nitrate of silver solution should
be filtered. A new sponge or a tuft of cotton is a good article to filter
nitrate of silver solution through. A small particle of light finding its
way upon the plate, will produce a spot. Another and very frequent cause
is, putting the slide of the tablet down rapidly, causing it to spatter
upon the plate the solution which has drained off from it. This paper
will be opaque when viewed by reflected light, and dark when viewed by
transmitted light. Occasionally a sort of transparent spot will appear:
this may be traced to a want of sensibility of the iodide of silver.
Large transparent spots frequently appear by the operator's pouring the
developing solution upon one place, and washing off the small quantity of
nitrate of silver necessary to develope the image. This will be easily
detected, and can be obviated by _flooding_ the most of the surface of the
glass with a steady stream of the developer.

Stains and Lines.--If the glass be allowed to rest for an instant with one
portion of its surface in the silvering solution and the other out of it,
it would cause a streak across; hence the necessity of totally immersing
it with one firm, steady motion removing the glass before it has been
thoroughly wetted, and the ether and alcohol allowed a uniform action over
the entire surface. A plate should not be disturbed in the bath until it
has been in a full minute at least.

_Irregular Lines_ are often caused by using the developing solution too
strong, or by not pouring it evenly over the plate at once. Should it be
allowed to rest in its progress, if but for an instant, it will leave its
line. Sometimes spangles of metallic silver appear: these are caused by
the presence of too much nitric acid in the developer for the proportion
of iodide in the film and the strength of the bath.

There are other phases connected with the practice of the positive
process, which it would be almost impossible to commit to paper, and
cannot be so explained as to be perfectly comprehended by the new
experimenter. It is absolutely necessary for all to observe every little
point noticed in the foregoing pages, and at the same time exercise
some good judgment, and no one need hesitate through fear of not being
successful.



                            PRACTICAL DETAILS

                                  OF THE

                           =NEGATIVE PROCESS.=



CHAPTER V.

NEGATIVE PROCESS--SOLUBLE COTTON--PLAIN COLLODION--DEVELOPING
SOLUTION--RE-DEVELOPING SOLUTION--FIXING THE IMAGE--FINISHING THE
IMAGE--NITRATE OF SILVER BATH.


Negative Process.

The manipulations and chemicals employed in the production of the negative
collodion pictures are very similar to those already given for operating
by the positive process; frequent reference will therefore necessarily be
made to portions of that process, as described in the preceding pages,
and only such parts will be given here, as do not correspond with the
foregoing.

It is thought advisable to omit in this chapter every reference that
does not have a desired tendency to aid the operator in the plain
straightforward order of manipulation. The negative process is fast
becoming popular and needs the attention of all who desire to keep pace
with the experiments in the art. Since the first edition of this work it
has been my pleasure to see many fine photographic specimens produced by
the following process, and no one need fail, if he will carefully adhere
to the details given.

There perhaps may be circumstances making it advisable for some to
have but one nitrate of silver solution for both positive and negative
collodion pictures: for such, a process will be given in the following
pages, which has recently appeared in _Humphrey's Journal_, and is called,
after its author, the "Helio Process," this is well adapted for most
purposes.


Soluble Cotton.

The method for preparing this has been given in page 41. It is prepared in
the same manner for both positives and negatives.


Plain Collodion.

The preparation of plain collodion employed is the same as that described
at page 53.


Developing Solution for Negatives.

  Rain or distilled water                             6 ounces.
  Protosulphate of iron                             300 grains.
  Acetic acid                                         2 ounces.

A little alcohol may be added to make it flow more evenly over the
plate--say 1 oz.

This solution can be kept in a pint bottle, and should have a funnel
devoted solely to the purpose of filtering it. One of the most convenient
dishes for receiving this solution, when poured over the plate, is a bowl
with a lip to it, as it can be readily poured back into the funnel.

The mode of employing this developer is the same as that for positives,
described at page 133. It may be used an indefinite number of times, but
should be kept clean; it soon assumes a red color.


Re-developing Solution.

This solution is for the purpose of giving increased intensity to the
negative, but as its use in the hands of beginners is attended with some
difficulty, I would not recommend the operator to try it until he has had
considerable experience in the developing process, or he will undoubtedly
spoil his proofs. Its use requires promptness of action and quick
observation.

The following is the formula for its preparation:

  Water                                               4 ounces.
  Protosulphite of iron                             400 grains.

Put this into a bottle, and when the crystals are dissolved, it is ready
for use. It should be kept filtered, and can be used only once. Now in
another bottle put

  Water                                               4 ounces.
  Nitrate of silver                                  48 grains.

Remarks.--The impression is to be well washed after the developing
solution has been poured off, and then the _re-developing solution_ (that
portion containing the protosulphate of iron) can be poured on--the plate
being held perfectly level: the surface is completely covered; the water
containing the nitrate of silver should then be poured _rapidly_ on, to
mix with the iron, when the surface of the impression will instantly
commence to blacken; and if the action be allowed to continue for a
lengthened period, say one minute, the impression will be ruined.

It is a matter worthy of notice, that there is no perceptible action
when the iron solution is poured over the glass; but the action is very
energetic the instant the nitrate of silver solution comes in contact with
the iron salt and the silver.

As soon as any change can be observed, after the re-developer has been
poured over the plate, it should be _quickly_ and copiously washed off
with clean water, and then it is ready for the fixing process.

I would dissuade novices in the art from practising with the
_re-developing solution_, until they have first thoroughly mastered the
entire process of taking negatives. The developing solution is the only
one used by operators generally, and will, with proper care, produce
satisfactory results.


Fixing the Image.

  Water                                               8 ounces.
  Hyposulphite of soda                                4 ounces.

Remarks.--This is nearly a saturated solution. The glass can be put in a
dish and the solution poured over, or held in the hand, in the same way
as the plate in the daguerreotype process. It can readily be seen when
a sufficient action has been attained, as the unaltered bromo-iodide of
silver will be dissolved, leaving only the reduced surface holding the
image.

This action should not be continued too long, as it affects the intensity
of the picture, injuring it for printing.

The glass should be well washed by pouring over it clean water, and then
it can be stood away to dry, in a _nearly_ perpendicular position, on
clean blotting paper, or otherwise, as is most convenient; when thoroughly
dry, it is ready for the finishing.


Finishing the Image.

This is done with the same material, and in the same manner, as that given
for positives--page 134.

Remarks.--The glass negatives, when not wanted for use, should be
carefully put aside in a box, and kept free from dust and dampness: by so
doing, it is believed that they will remain good for any length of time.


Nitrate of Silver Bath.

This solution differs only from the positive bath, by omitting the _nitric
acid_: in all other respects it is precisely the same, and is prepared by
the same formula, as given at page 64.

This is called the _neutral bath_, and is best adapted to the negative
process. The nitrate of silver employed in its preparation should be
perfectly free from excess of nitric acid, otherwise the whole solution
will be slightly acid.

If it should not be convenient to obtain nitrate of silver without this
objection, the acid may be neutralized by putting into the solution a
small quantity of common washing soda-- say 1 grain to each 100 grains of
nitrate of silver--previously dissolved in about half an ounce of water.
This may be put in at the same time that the iodide of potassium is, and
it would save one filtration.

In twenty samples of nitrate of silver that I have tried the above
quantity of soda has been found sufficient; if, however, the _white_
precipitate first formed is re-dissolved on shaking the mixture, free
nitric acid is present, and more of the soda may be added.

This bath will improve by age, and be less liable to fog after having been
in constant use for one or two weeks.

Operators who have the means, and design following the art professionally,
will find it to their advantage to make from two to three times the
quantity of solution they require for immediate use: by this means
they will be enabled to replenish their stock, which may be used up or
otherwise lost.



                            PRACTICAL DETAILS

                                  OF THE

                           =PRINTING PROCESS.=



CHAPTER VI.


PRINTING PROCESS--SALTING PAPER--SILVERING PAPER--PRINTING THE
POSITIVE--FIXING AND COLORING BATH--MOUNTING THE POSITIVE.


The Printing Process.

[Sidenote: MANIPULATIONS OF THE PRINTING PROCESS.]

There is probably no department of the photographic art where can be found
an equal amount of variety, as regards chemicals, manipulations, etc.
The course adopted in the commencement, of giving only one process for
the operator to work by--and that a good one--will be strictly adhered
to in this place. I have produced as good positives on paper by the
following plan, as I have ever seen. Should the reader wish more extensive
acquaintance with the printing processes, he is referred to Humphrey's
Journal.


Salting Paper.

  Water                                               1 quart.
  Muriate of ammonia                                 65 grains.

The water is put into a flat, gutta-percha, glass, or earthen dish, and
the muriate of ammonia is put into it, and stirred until it is dissolved
and is well mixed with the water; then proceed as follows: we will suppose
we have a gutta-percha dish sufficiently large to take in a sheet of
paper 8 by 10 inches, and about 1-1/2 or 2 inches deep: take hold of two
corners of the paper with the thumb and finger of each hand, and then
draw the paper through the solution, by passing it from one end of the
dish to the other, so that it will be wetted on both sides; then turning
it over in the same manner, draw it back, so that its surface will be
thoroughly moistened, but it is not necessary to _saturate_ the paper.
Now the paper is ready for drying, which may be done by hanging it on the
edge of a shelf by means of little tack nails put through it at the same
corners by which it was held in passing through the salting solution. In
order to prevent streaks, from forming upon the paper, it is better to
hang it in such a manner that it cannot touch the shelf, except at the
corners: say the sheet is eight inches wide, and the tacks (which are put
through the corners) to be only five or six inches apart, this will give
the proper bend outwards, preventing its contact with the shelf. This
entire operation can be performed in daylight, or otherwise as suits the
convenience of the operator.

This paper, when dry, should be laid between the folds of blotting paper
(filtering paper will answer), and may be kept for any length of time, and
is ready for the silvering process.


Silvering Paper.

In silvering paper, I employ the ammonio-nitrate, which is prepared as
follows:--

  Water                                               2-1/4 ounces.
  Nitrate of silver                                  75     grains.

Dissolve (in a 4-ounce vial) the nitrate of silver in the water, and then
pour one-fourth of the solution into an ounce graduate or any convenient
vessel: this keep for farther use in preventing the presence of an excess
of ammonia. Now, into the bottle containing the three-fourths put about
4 drops of aqua-ammonia; shake well and a brown precipitate will be
given. Continue adding the ammonia, _drop by drop_, and shake after each
addition, until the brown precipitate is re-dissolved and the solution is
clear; then pour back into the bottle the one-fourth taken out at first:
this will leave the solution slightly turbid, and when so, there is no
excess of ammonia which would be objectionable. It may now be filtered
through filtering paper, and it (the clear liquid) is ready for use. This
should be kept in the dark, as it decomposes rapidly when exposed to light.

The method of silvering the paper with ammonio-nitrate of silver, is as
follows: take a tuft of clean cotton, roll it into a ball-shape, then
wet it by holding it against the mouth of the bottle containing the
ammonio-nitrate, and when well wet, apply it to the paper (which should be
placed flat on a clean board) by gently rubbing it over the surface, care
being taken not to roughen it.

If the solution has not been filtered for some time, it would be advisable
to pour a little on the centre of the paper, and then distribute it over
the surface by means of the cotton, which is held in the fingers: by this
last method any sediment which may be in the bottom of the bottle is
prevented from getting upon the paper, and causing spots.

I have used a brush for the purpose of distributing the solution, by which
plan there is less liability of getting it on the fingers and staining
them. Care must be taken to cover the _entire surface_ of the paper, or
there will be light streaks, occasioned by the absence of the silvering
solution.

This want of silver will appear on the paper in light parts, as seen in
the accompanying cut:

[Illustration: Fig. 36.]

After the paper has been perfectly coated, or washed with the silvering
solution, it should be placed in a perpendicular position to dry. I
usually tack the paper on a board of the requisite size, and then stand it
on one edge until it has drained and dried. As soon as dry, it is ready
for use. This paper will not keep more than twelve hours, therefore the
operator should silver in the morning the quantity required for the day.
It is imperatively necessary that the silvered paper be kept in the dark.
It is extremely sensitive to light, and a very brief exposure of the
prepared sheet would render it unfit for use.


Printing the Positive.

The several kinds of apparatus used for holding the negative and the
sensitive paper together, have already been given on page 36, Figs. 31,
32, 33. The paper having been salted and silvered, as just described,
should be placed on the pad of the printing frame or glasses, with its
sensitive surface up, and then the negative placed directly upon and in
contact with it; then it is to be fastened together, when it will be ready
for exposure to the direct rays of the sun. From 10 to 40 seconds will be
found enough to give a sufficiently intense print.

The paper first changes to a slate color, and then to a brown or copper
color t when of a dark slate color is about the proper time to take it out
and immerse in the toning bath.


Fixing and Coloring Bath.

I have employed the proportions given by Mr. Hardwich in his _Photographic
Chemistry_, page 209--Humphrey's American edition.

  Solution of chloride of gold, a quantity
    equivalent to                                     4 grains.
  Nitrate of silver                                  30   "
  Hyposulphite of soda                                2 ounces.
  Water                                               8   "

"Dissolve the hyposulphite of soda in four ounces of the water, the
chloride of gold in three ounces, the nitrate of silver in the remaining
ounce; then pour the diluted chloride by degrees into the hyposulphite,
stirring meanwhile with a glass rod; and afterwards the nitrate of silver
in the same way. This order of mixing the solution is to be strictly
observed; if it were reversed, the hyposulphite of soda being added to
the chloride of gold, the result would be the reduction of metallic gold.
The difference depends upon the fact that the hyposulphite of gold which
is formed is an exceedingly unstable substance, and cannot exist in
contact with unaltered chloride of gold. It is necessary that it should be
dissolved by hyposulphite of soda _immediately_ on its formation, and so
rendered more permanent by conversion into a double salt of soda and gold.

"The _time of coloration_ depends much upon the quantity of gold present,
and may in some cases be extended to many hours. The results of a few
experiments, performed roughly, appeared to indicate that the activity
of this bath is less affected by depression of temperature than those
prepared with tetrathionate. Certainly the injurious effects of prolonged
immersion are not so evident as with the first two formulæ: the purity of
the whites remains unaltered for many hours if the bath is new, but with
an old bath there is a tendency to yellowness, which is probably caused
by the presence of sulphuretted hydrogen. Fresh chloride of gold must be
added from time to time, as it appears to be required."

After the impression has remained in the toning bath a sufficient length
of time, it should be placed in a dish or sink of clean water, which
should be changed several times--floating for at least 12 hours; then it
may be taken out and hung up to dry.

"Touching."--The _coloring_ of a photograph forms no part of my process:
this is a matter to be given into the hands of an artist, and when it
bears the finishing touch of his skill, it is no longer a _photograph_,
but _an oil_ or _watercolor painting_; all the delicate workings of nature
having been lost or hidden under the colors.

A photograph may often be "touched" to advantage. If, as is frequently the
case, there be little white spots on the face of the paper, they may be
readily covered by the application of a little India ink, with the point
of a wet pencil or fine small brush.


Mounting of Positives.

This, though a small matter in itself, is worthy of great attention. The
durability of the proof depends much upon the purity of the paste used in
causing its adhesion to the Bristol board. I have employed the following
composition with the most eminent success:--

  Gum arabic                                          2     ounces
  Gum tragacanth                                      1-1/2   "
  Isinglass                                           1-1/2   "
  Sugar                                                 1/2   "
  Water                                               3     pints

These ingredients should all be dissolved, and then boiled down to the
proper consistency, by means of a gentle heat.

I will give another composition, which will serve a good purpose, and keep
for a long time:--

  Water                                               8 ounces.
  One table spoonful of wheat flour
  Powdered alum                                      40 grains.
  Powdered resin                                          "
  Brown sugar                                         1 ounce.
  Bichloride of mercury                              20 grains.

This last composition may be more convenient for operators, and it will
answer the purpose well. It is thought by some to be the _best_ and _most
durable_ paste yet prepared for the purpose.



=FACTS WORTH MENTIONING.=

[Sidenote: FACTS WORTH KNOWING.]


_The Poisonous Effects_ of cyanide of potassium upon sores, may be
obviated by immediately applying some of the positive developing solution,
described at page 62. By this means much annoyance may be avoided to
persons afflicted with chapped or sore hands.

_Bending Glass Rods_ or tubes can be easily done by subjecting them
to the blaze of a spirit lamp--the same as that used for gilding the
daguerreotype. First hold the rod just above the blaze, then gradually
allow it to descend into it, imparting to the rod a rotatory motion with
the finger and thumb: this will soon cause a softening of the glass, when
it may be bent to any desired shape. If the ends are to be bent to form
hooks, another small piece of glass, or any warm metal, may be placed upon
the end, in the blaze of the lamp, and as soon as thoroughly softened, it
can be pressed or bent to form the hook. By filing around a glass tube or
rod, it may be easily and safely broken at the desired point, by giving it
a sudden jerk between both hands, holding it close to the encircled part.

_Cementing Glass_ may be readily accomplished by placing the two ends
together in the blaze of the lamp, and holding them there until they
attain a sufficient degree of heat to slightly fuse: when cool, the ends
will be found perfectly united.

_The Background_ best adapted to positives is unbleached muslin, such, as
is sold for sheeting, and can be found in almost any dry goods' store:
it should be from two to three yards wide. A clouded appearance is given
to the background by merely marking it with _charcoal_, forming streaks
or "_waves_" resembling clouds. These come out black, or dark, in the
positive, and give a variegated appearance. The roughness of the marking
does not matter, since the background is generally a little out of the
focus of the lenses. Trees and other designs may be represented in this
matter.

_Positive Collodion Pictures_ may be whitened by the use of bichloride of
mercury, thirty grains to one ounce of water. After the picture has been
developed, fixed and washed, by the process given in the preceding pages,
the solution of bichloride of mercury may be poured over the surface of
the image: it almost immediately presents a series of interesting changes
in color. The surface at first blackens but for a few minutes, when it
begins to get lighter, and gradually brightens to a pure white, inclining
to a blue. It should then be thoroughly washed and dried, as usual.

_Instantaneous Pictures_ may be taken by employing the _iodide of iron_ in
the collodion. The best method with which I am acquainted, is to have a
saturated solution of iodide of iron in alcohol, and drop one or two drops
into an ounce of the collodion (which has been previously iodized) used
in taking positives. This can be used at once, as soon as mixed. No more
of this collodion should be prepared than is wanted for immediate use, as
it will keep good for only a few hours. The saturated solution of iodide
of iron can be kept on hand ready for use at all times. There should be
an excess of the iodide in the alcohol. The same accelerating effect is
produced with the negative collodion prepared in this way.

_Plain Collodion_ may be iodized as soon as dissolved: this will save time
in settling. It is a fact that some cotton is more readily dissolved when
the bromo-iodizing is present: but by the addition of this, I have often
taken up considerable quantities of the gummy sediment remaining in the
bottom of bottles.

_Prepared Glass_ may be preserved clean and free from dust by keeping in
boxes such as those used for keeping daguerreotype plates. By taking out
every other partition between the grooves, the glass can be readily put in.

_Collodion Vials and Bottles_, after having collodion in them once, should
be rinsed with alcohol and ether (in the same proportions as employed for
dissolving the cotton), before using them a second time for that purpose.
Penuriousness in this respect would be bad policy.

_Coating Large Glasses._--A convenient method of doing this is represented
in the following illustration:

[Illustration]

The glass is held by one corner, 2; the other corner, 4, is rested on a
table or bench, and the collodion poured on, so that the excess may be
poured off at 1.

_Black Stains_ upon the hands, caused by nitrate of silver, may be removed
by moistening them and rubbing with a lump of cyanuret of potassium. This
salt is poisonous, if used to a great extent [_See page 139_]. Another
safer, but more expensive plan, however, is to take a saturated solution
of iodide of potassium in water, and then wash with nitric acid diluted
with two parts water.

_Stains upon White Linen_ can be removed by washing with a saturated
solution of iodide of potassium containing a little iodine; then wash with
water, and soak in a saturated solution of hyposulphite of soda until the
yellow iodide of silver is dissolved.

_The hands_ should always be washed after fixing a positive or negative
picture, before again touching a glass to be coated, or the dipper; this
precaution is necessary, lest any of the iron salt, or the hyposulphite,
should get into the silvering solution and spoil it.

_In taking Collodion Pictures_, it is always advisable for the sitter to
be arranged before the glass is taken from the bath: this will save time
and there will be less liability of the collodion drying.

_A Good Negative_ may be known by its possessing the following
characteristics:--By transmitted light the figure is bright, and appears
to stand out from the glass; the dark shadows are clear, without any misty
deposit of metallic silver; the high lights black almost to complete
opacity.

_A Glass Coated with Collodion_, if kept too long before immersion in the
bath, will not be equally sensitive over its surface; the parts most dry
being the least sensitive.

_Glass Pans, for Scales_, can be procured by every one at trifling
expense: Take a watch crystal, and place in the common metal pan; balance
this with lead, or any weight: this can easily be kept clean, and is the
most advisable for weighing all deliquescent salts, and chemicals employed
in the collodion process.

_Caution._--Persons engaged in making collodion, and using ether and
alcohol, must bear in mind that these chemicals are _very inflammable_;
hence extreme caution is necessary to avoid exposing them to the flame of
a lamp or candle. I have known of several serious accidents, of recent
date, all of which were caused by the imprudence of the experimenter in
the particular above mentioned.

_Wipe the Plate-holder_ every time before the glass is put into it: this
will prevent spots, which might otherwise occur from the presence of
nitrate of silver solution which drained from the plate previously used.
These spots are of an opaque yellowish tinge, and in shape resemble the
stain which would be occasioned by a _splash_ of water.

_Glass jar Positives._--A good _white_ or light-green glass will answer
for the collodion coating. Glass which contains air-spots can be used, if
it be placed in such a manner as to let the light of the image come over
them, as the spots cannot be seen through the opaque surface. Only the
best white glass should be used for _covering_ the picture. Some operators
use the convex glass, which is very clear, and answers the purpose.

_The Nitrate of Silver Bath_ should be kept covered, except when in use.

_If a Glass be Immersed too soon_, streaks and waves will be occasioned.
These will be seen at the end of the plate which is least dry: the coating
is also more liable to peel off. It should be borne in mind, however, that
the peeling of collodion is not always attributable to this cause.

_Diffused Light in the Developing Room._--In proportion as the
sensitiveness of the plates increases, greater care must be exercised
in thoroughly excluding all rays of white light. With opalescent films,
neutral, this cause of fogging is more common than any other.

_Tn the case_ of a portrait, if the features have an unnaturally black and
gloomy appearance, the dark portions of the drapery, &c., being invisible,
the picture has been _underexposed_ in the camera.



CHAPTER VII.


=HELIO PROCESS.=[F]

[Footnote F: It has been thought advisable to publish in this work
the _Helio Process_, and I do so just as it appeared in _Humphrey's
Journal_.--S. D. H.]

An Entire Process for Producing Collodion Positives and Negatives with
one Bath, and in much less time than by any other known Process.--By
Helio.--Photographic Patents.

                                              Boston, Oct., 1856.

  S. D. Humphrey.

_Sir_,--As _Humphrey's Journal_ is the only truly progressive and
independent Photographic publication in America, I feel it the duty of
every one to aid its Editor in furthering the interest of the amateur and
practitioner of the art; and, suiting the action to the word, I present
the following Process as being worthy of confidence, and having, in my
hands, proved eminently satisfactory. I am surprised to see that Operators
and men respectably connected with the practice of the Art should so far
fall beneath the station of true artists as to advertise to catch each
other, or the verdant ones, by offering this or that little improvement
all "printed complete for five dollars." As an amateur, and having the
good of the science I love at heart, I now contribute my mite for the
benefit of all interested; and, following the glorious example of G. B.
C. (who I hope we shall soon hear from again,) in your last, I say--God
speed!

I shall endeavor to be as minute and concise as possible, so as to enable
any one to adopt and successfully use my processes.

_Preparation of Soluble Cotton._--I put into a Wedgewood mortar, twelve
ounces, by weight, of dry and finely pulverized nitrate of potash (I
use Dupont's refined), and add to it twelve ounces, by measure, of good
commercial sulphuric acid; I mix these well together by the use of a glass
rod and pestle, so that it forms a paste; I then add, in small quantities
at a time, about 325 grains of good coarse cotton (this is according to
your process), and _knead_ the mass well for from three to five minutes;
and then cover the mortar with a piece of glass, and let it stand for
twenty or thirty minutes, by which time it will have been sufficiently
acted upon. Then the cotton is to be plunged into a quantity of clean
water and thoroughly washed in a number of changes of water, so that when
it is squeezed between the folds of blue litmus-paper it will not redden
it; this indicates that the acid has been washed out; I then place the
cotton in a clean strong towel and wring out all the water I can, then put
it into alcohol, then wring it again, and adopt your plan of not letting
it become thoroughly dry.

The cotton being now ready for use, I dissolve it in the following
mixture, in a bottle of proper size:--

  Sulphuric ether                                   10 ounces.
  Alcohol, 95 per cent.                              5 ounces.
  Soluble cotton, enough to make it about as
    thick as cream.

The above should be well shaken, and then allowed to stand for one or two
days to settle. This constitutes my Plain Collodion, and should be poured
off into another bottle, leaving the sediment behind.

_Iodizing._--For this purpose I employ the following preparation:--

_A._--_Iodide of Silver._--Dissolve fifty grains of nitrate of silver,
crystals, in two ounces of pure water, and forty grains of iodide of
ammonium in two ounces of pure water; then pour the two together, shaking
the mixture well; let it settle, which it will do in a few minutes; then
pour off the water carefully, leaving behind all the yellow iodide of
silver; pour again a fresh quantity of water over the precipitate, and
continue this washing for at least six changes of water; then drain off
the water as close as possible and pour on two ounces of alcohol, which,
when drained off, will leave the powder sufficiently clean for the purpose.

_B._--I now dissolve forty grains of bromide of ammonium and one hundred
grains of iodide of ammonium in two ounces of 95 per cent, alcohol, and
then add the iodide of silver (preparation _A_), and shake the whole well
together, giving a saturated solution. This is to be filtered through
cotton or paper, when it will be ready for use.

_C._--To sixteen ounces of Plain Collodion add from eight to twelve drops
of tincture of iodine (50 grains of dry iodine dissolved in half an oz. of
alcohol) and 14 grains or drops of fluoride of ammonium; shake the mixture
well; then add all of the solution _B_; shake it again and thoroughly;
after this has stood for twenty-four hours it can be used, but will be
found better after it has been prepared one week.


Nitrate of Silver Solution.

  Pure rain or distilled water                       64 ounces.
  Nitrate of silver (in crystals)                     4-1/4 ounces.
  Clean pure white sugar                             75 grains.
  Six grains of iodide of ammonium dissolved in
    half a drachm of alcohol.

The above, thoroughly mixed and allowed to stand for a few hours, should
be filtered through a new clean sponge, asbestos, or Swedish filtering
paper, and then a few drops of nitric acid, chemically pure, should be
added, just enough to redden blue litmus-paper; then it is ready for use,
and will improve by age.

_Developing Solution._--This formula has proved very satisfactory in my
hands, and I hope will be equally so with all who give it a trial:--

  Water                                               1   pint.
  Boracic acid                                        3/4 ounce.
  Protosulphate of iron                               3/4 ounce.
  Pulverized nitre                                    1/2 ounce
  Three drops of oil of cinnamon dissolved in two
    ounces of alcohol.

Dissolve and filter, and it is ready for use. It is better to make this
developer fresh every other day.

_Dissolving off the Iodide of Silver._--Water, about half a pint; cyanide
of potassium, enough to clear the impression in about thirty seconds--say
a quarter of an ounce.

_Fixing the Impression._--I use the article well known to every good
photographer as Humphrey's Collodion Gilding, and it serves the purpose
better than anything that I I know of.

_Black Varnish._--I generally purchase this from the dealer; but I have
made an article which answered the purpose well, by dissolving pulverized
asphaltum in spirits of turpentine. Any of the black varnishes can be
improved by the addition of a little bees'-wax to it. It is less liable to
crack and gives an improved gloss.

_Negative and Printing Processes._--Being myself an amateur, and desiring
to study economy and convenience, my attention has been given to the test
of numerous plans for avoiding the necessity of two baths and silvering
solutions and I feel confident that the amateur will find the following,
in connection with the foregoing Positive Process, the best adapted to his
wants.

The same bath and solution is used for the negative as for the positive
process; and the time of exposure in the camera should be prolonged a few
seconds. I have produced beautiful negatives, in-doors, in _four seconds_,
and, out-doors, _instantaneously_. The manipulation, bath, and developing
solution are precisely the same as those used in the positive process.

_Fixing the Negative._--Place the following mixture in a well-stoppered
bottle:

  Pure Water                                          6 ounces.
  Aqua-ammonia, concentrated                          1 ounce.

This solution should be poured on the negative and allowed to remain for
about twenty seconds. It should be borne in mind, that the developing
solution (same as for positives) should be well washed off the glass
before the fixing solution is poured over; after it has remained on the
glass for the time given (20 seconds), the negative can be washed with
clean water and dried; it is then ready for printing. The iodide of
silver is not, as in other processes, dissolved off, but remains on the
glass.

It sometimes happens that the negative is not sufficiently intense; this
result can be obtained by pouring over the plate the following solution,
which should remain for about three-fourths of a minute:

  Water                                               8 ounces.
  Nitrate of silver                                  28 grains.
  Alcohol                                             1 ounce.
  Loaf sugar                                        1/3 ounce

After this solution is used, I pour over the impression the developing
solution, and then wash well with water. This re-developing may be
repeated two or three times, and almost any desired intensity obtained.

_Printing Process--Salting the Paper._--Boil the following mixture in an
earthen vessel until it becomes transparent:--

  Distilled water                                    12 ounces.
  Muriate of ammonia                                240 grains.
  Arrowroot                                         112 grains.

After this has been sufficiently boiled, it should be strained through
clean linen or cotton cloth (free from soap or other substances), and,
when cool, it is ready for coating the paper, which is done by dipping a
new clean sponge into it and rubbing it over one side of the paper, giving
it a uniform coating; but as it is not desirable to have too much on the
paper, it should be rubbed with a clean sponge until nearly dry; it can
then be hung up by the corner until thoroughly dry, when it can be put
into a portfolio and kept for exciting for use.

_Silvering Solution._--This solution may be prepared in the light, but
must be used in a dark room:--

  Distilled water                                     1 pint.
  Nitrate of silver                                   3-3/4 ounces.

Dissolve and pour into an earthen or gutta-percha dish. Take the paper
(cut to the proper size) and _float_ it on this solution for about three
minutes; care must be observed that there are no air-bubbles between the
solution and the paper, for this would cause spots. It now can be hung up
to dry, and as soon as dry it may be used. Let me here repeat, that this
operation must be conducted in a dark room.

_Fixing and Toning Bath._--I find that a better effect is produced if the
positive be a little over-printed before being acted upon by the following
mixture:--

  Distilled water                                     8 ounces.
  Chloride of sodium                                240 grains.

This solution should be put into a flat dish and the print placed on it,
face down, for from one and a-half to three minutes, when it should be
taken off and put into the following solution, and allowed to remain there
from three quarters of an hour to two hours:--

  Distilled water                                    18 ounces.
  Hyposulphite of soda                                3 ounces.
  Nitrate of silver                                  60 grains.

The following method should be observed in preparing this last mixture,
viz.:--dissolve the three ounces of hyposulphite of soda in _sixteen_
ounces of the water and the sixty grains of nitrate of silver in the
remaining two ounces; then pour the nitrate of silver solution into that
containing the hyposulphite of soda, stirring the mixture continually
until all is well mixed.

After the print has remained in the toning solution for the specified
time, it should be taken out and well washed in several changes of clean
water, and dried and mounted in any of the usual ways.

With a few general remarks I will close this, perhaps, too long
communication. It should be a point in the practice of every one who
desires success in any process, to maintain a strict observance to
cleanliness; this is one point in which most persons fail, and it cannot
be too strongly impressed upon the minds of manipulators. It should be
understood that the foregoing process is _complete in itself_, and is not
to be confounded with any other method. The _collodion_ is adapted for
the _nitrate of silver bath_, and the _bath_ for the _collodion_; and no
one should use other preparations of collodion and silvering solution,
except they do so with the full expectation that it will be at the _loss
of either or both of the preparations employed_.

Allow me, through the columns of your invaluable Journal, to say to
those who may read the foregoing process, that if they find (as I have)
my process to prove profitable to them, I shall consider myself amply
repaid if they will, through the same medium, contribute to our stock
of information by giving an account of their experiments. I feel quite
confident that some of the amateurs, with whose reputation I am already
acquainted, and of whose private works in photography America has cause to
feel proud,--could furnish interesting, useful and valuable information
upon this subject. Such men, for instance, as G. B. C, of Md. (who has
already made a good beginning), G. W. D., of the same place, and Mr. G.
G., of Pa. Friends and co-laborers, shall we hear from you? I pause for a
reply!

I look with interest upon every stroke of the pen from your able
correspondent G. M., of Washington, whose specimens of photographic
engraving you recently had the kindness to show me. I assure you, it did
not a little astonish me to witness the surprising truthfulness with which
the details were presented.

                                                        Helio.



=CORRESPONDENCE=

BETWEEN THE U. S. COMMISSIONER OF PATENTS AND JAMES A. CUTTING, RELATIVE
TO HIS APPLICATIONS FOR LETTERS PATENT.

                              United States Patent Office, April 17, 1854.

Sir: Your application for letters patent for an alleged improvement
in making photographic pictures, having been submitted to the proper
examiner, is rejected. As the use of alcohol to absorb water in hasty
desiccation is understood to be commonly practical in most chemical
laboratories, no reference is thought necessary for the rejection of the
first claim.

Secondly, the mixture of alcohol and ether in unlimited proportions to
dissolve gun cotton for photographic purposes, is common. [_See_ Gaudin's
Process, "Humphrey's Daguerreian Journal," vol. 4, p. 229.]

Thirdly, collodion with bromide basis, is not new. [_See_ General Remarks
on Collodion, by Gaudin, "Photographic Art Journal," 1st Series, vol. 6,
p. 348.]

The two articles above referred to are translated from the French, and
contain also, it is believed, sufficient to show that the subject of the
fourth claim has been anticipated, rendering further reference unnecessary.

                   Respectfully yours, &c.,
                            S. F. Shugert, Acting Commissioner.

  J. A. Cutting (care of C. G. Page), Washington, D. C.

       *       *       *       *       *

                                                            Jane 17, 1854.

Sir: In regard to the use of bromide bases with collodion, I am prepared
to show that I had it in successful use in the month of April, 1853;
and if the circumstances require legal proof of the same, it will be
furnished, though at some expense of time and money to me; and as the
question is only between the public and myself, I trust the office will
see fit to grant me a patent for the same.

                                                         James A. Cutting.

  Hon. Chas. Mason, Commissioner of Patents.

       *       *       *       *       *

                              United States Patent Office, April 19, 1854.

Sir: In your letter of the 17th, you say that, if necessary, proof can
be given that you had in successful use, in the month of April, 1853,
collodion prepared with a bromide oasis. On referring to the "Journal of
the Photographic Society," of London, No. 6 (June, 1853), page 70, you
will see that Sir John Herschel used bromide for the same purpose previous
to the year 1840. Ammonia, in various combinations, has long been in use
for the preparation of sensitive collodions. [_See_ Report of the British
Association, 1850, p. 150, "Journal of the Photographic Society" No. 9,
1853, p. 116.] F. M. Lyndes' process and compositions show that he has
used iodine, bromide, and chloride of ammonium; and Count de Montegon, in
the same journal, No. 2, April, 1853; page 24, for his fifth composition
of collodion, used liquid ammonia. These are all regarded as equivalents
for your compositions covered by the fourth claim; if, however, there is
a difference, you are at liberty to show in what it consists; and the
examination is accordingly postponed to await your action.

                                     Yours, &c.,
                                          C. Mason, Commissioner.

  J. A. Cutting (care of C. G. Page), Washington, D. C.

       *       *       *       *       *

  Washington, June 21, 1854.

Sir: In reply to your communications of the 19th instant, and April 17th,
1854, I propose to modify my claims as follows, to wit:

After the first clause of the claim, nineteenth line, ending with the
words "set forth," add as follows: "I do not claim the use of alcohol as a
_desiccating agent_, but limit my claim to its special use and purpose, as
herein stated."

Erase the fourth clause of the claim, commencing on the twenty-sixth line,
and ending with the words "set forth" on the thirtieth line.

In reply to the objection raised by the office that "bromide was used
in 1840," I have to say that I was fully aware of the employment of
bromide in various ways for photographic purposes, and that I have also,
in common with photographers, known the extreme difficulty of using
bromide, and that notwithstanding the sensitiveness imparted by bromide
to other compounds, it has been almost universally discarded by practical
photographers. The discovery of collodion as a vehicle for sensitive
materials is of recent date, and there seems to have been a backwardness
on the part of photographers to attempt bromide bases with collodion, and
so far, whatever trials have been made subsequent to my discovery, it is
evident that they have been attended with the results of "misty pictures."
To whatever my success may be due, I maintain that I have been the first
to use a bromide base with collodion--and with that only do I claim
it--and the results in my pictures show with what success.

                          Respectfully,
                                 James A. Cutting,
                                      By Att'y, Chas. G. Page.

  Hon. Chas. Mason, Commissioner of Patents.

       *       *       *       *       *

                               United States Patent Office, June 21, 1854.

Sir: Your specification of an improvement in composition for producing
photographic pictures is herewith returned for a slight amendment, which
is, to omit the reference to specimens which do not accompany the patent,
and to correct an error in the oath as noted on the margin.

                                 Yours, &c.,
                                     C. Mason, Commissioner.

  James A. Cutting, 142 Hanover st.; Boston, Mass.

       *       *       *       *       *

                               United States Patent Office, June 22, 1854.

Sir: By reading a paper by Mr. W. Crookes in the "Journal of the
Photographic Society, London," No. 7, p. 86, "on the employment of bromine
in collodion," it is believed you will be satisfied that the date there
given on which he used bromized collodion is prior to your claim to
having used it; he refers to p. 72, No, 6, published in June, 1853, for
experiments made with bromized collodion, which paper is dated June 2d,
1853. Mr. Isaac Rehn, of Philadelphia, has testified to having seen you
make use of a bromide base, viz., bromide of potassium and collodion,
about the 1st of July, 1853, or about one month after the date of Mr.
Crookes' paper in England. The specification is accordingly returned, that
you may cancel the fourth claim, and amend the papers to suit.

                               Yours, &c.,
                                   C. Mason, Commissioner.

  Mr. J. A. Cutting, (care of C. G. Page), Washington, D. C.

       *       *       *       *       *


PATENT FOR THE USE OF CAMPHOR IN COMBINATION WITH IODIZED COLLODION.

The schedule referred to in the Letters Patent, and making part of the
same.

_To whom it may concern:_

Be it known, that I, James A. Cutting, of the City of Boston, County
of Suffolk, and State of Massachusetts, have invented a new and useful
improvement in positive photographic pictures on glass, and I do hereby
declare the following to be an exact description thereof:

The nature of my invention consists in the use of gum camphor, in addition
to the existing materials in the preparation of collodion for positive
photographic pictures on glass.

To enable others skilled in the art to make and use my invention, I will
proceed to describe the process as follows:

Having prepared the collodion in the usual manner, I take a pint bottle,
in which I introduce twelve ounces of collodion, to which I add one drachm
of iodide of potassium, dissolved in alcohol. I then shake the mixture
thoroughly, and add thereto eighteen grains of refined gum camphor,
shaking the mixture again, until the whole is combined, then allow it to
settle, when it is lit for use.

The advantages of my improvement consist in the increased vigor of the
delineations of the half-tones of positive pictures on glass, giving
greater depth and rotundity thereto, which render this combination
exceedingly useful for microscopic pictures, as well as the ordinary
purposes of portraiture.

T would have it understood that the combination of camphor with iodide
of potassium and collodion, as above specified, is adapted solely to the
production of positive pictures on glass and not to the production of
negative pictures on glass, from which positive pictures on paper may be
printed, as a sufficient degree of opacity is not thus afforded for that
purpose.

What I claim as my invention, and desire to secure by Letters Patent, is
the use of camphor, in combination with iodized collodion, as set forth in
the specification.

                                                James A. Cutting.

  Samuel Grubb, } _Witnesses._
  I. Rehn.      }

  _Dated, July 4th, 1854._

         *       *       *       *       *


PATENT FOR THE USE OF BALSAM FOR SEALING PHOTOGRAPHIC PICTURES ON GLASS.

The schedule referred to in Letters Patent and making part of the same.

_To whom it may concern:_

Be it known that I, James A. Cutting, of Boston, in the County of Suffolk
and State of Massachusetts, have invented new and useful improvements in
photographic pictures on glass, and I do hereby declare the following to
be an exact description thereof:

The nature of my improvement consists in the application of a coating of
balsam of fir to the side of the glass on which the picture is made, over
which coating I place another glass of equal size with the one on which
the picture is.

To enable others skilled in the art to make and use my invention, I will
proceed to describe the process as follows:

After thoroughly cleaning a glass plate of the same size as that on which
the picture to be secured is made, and moving all dust from the picture,
I hold the glass containing the picture in a horizontal position with the
pictured side uppermost, then apply the balsam in a line along one edge
of the glass and placing one edge of the second glass in close contact
with the first, containing the balsam, press them gradually together
towards the opposite edge, causing the balsam to flow by a gentle pressure
towards the opposite edge, in this manner excluding all air from between
the glasses; then by an even pressure exclude the superabundant balsam.
The advantages of my improvements are, that by a mechanical combination
of the balsam with the picture it is greatly increased in strength and
beauty, by an additional brilliancy and the exhibition of the most minute
delineations; and by the application of the second glass in combination
with the balsam, the picture is hermetically sealed and rendered entirely
permanent, by being secured from the influence of both air and moisture,
and also from injury by dust or other extraneous matter, or acid vapors,
or any violence less than what could occasion the fracture of the plate
glass.

I am aware of the previous use of balsam for the cementing of lenses and
the securing of microscopic objects, and other like purposes, and do not
therefore extend my claim to any of these uses; but

What I claim as my invention, and desire to secure by Letters Patent, is
the combination of balsam with photographic pictures on glass, and with
additional glass by which they; with the balsam, are hermetically sealed,
as described in the specifications; and for the purposes therein set
forth, and for no other.

                                                James A. Cutting.

  Issac Rehn,   } _Witnesses._
  Samuel Grubb. }

  _Dated July 11th, 1854._

       *       *       *       *       *


PATENT FOR DISPLACING WATER FROM SOLUBLE COTTON BY THE USE OF ALCOHOL;
ALSO, FOR THE USE OF BROMIDE OF POTASSIUM IN COMBINATION WITH COLLODION.

The schedule referred to in these Letters Patent, and making part of the
same.

_To all to whom these presents shall come:_

Be it known that I, James A. Cutting, of Boston, in the County of Suffolk
and State of Massachusetts, have invented certain improvements in making
photographic pictures, and that the following is a full, clear and exact
description of the principle or character which distinguishes them
from all other things before known, and of the usual manner of making,
modifying, and using the same.

My improvements relate to that class of photographic pictures in which the
pictures are obtained upon a prepared film of glass or other substance.

The film which I employ is collodion, and in order to insure success, the
collodion must be prepared after my own process, as follows: Take 3 ounces
(Troy) of pure dry nitrate potassa, and pulverize in a clean glass mortar;
add to this 2-1/2 ounces, fluid measure, of pure sulphuric acid, and stir
the mixture with a glass rod; immerse in this liquid, 80 grains of clean,
dry cotton, and knead the mass of cotton in the liquid for about Ave
minutes; remove the cotton and quickly wash it, till every trace of acid
is gone, and it must then be dried quickly--for I have discovered that the
more rapidly the cotton is dried, the more sensitive the collodion; and
I have found the best effects produced by displacing the water from the
cotton by strong alcohol.

To prepare the collodion, take 10 ounces concentrated sulphuric ether, 60°
Baumé, and mix this with 6 ounces of 95 per cent. alcohol. To this mixture
add the prepared cotton, in quantity sufficient to make a collodion as
thick as it can, and yet at the same time flow evenly over the surface of
glass. Let it settle clear, and decant the solution.

In order to "excite" this collodion, take a deep 1 ounce vial--introduce
2-1/2 grains of bromide of potassium, and add water, drop by drop, to make
a saturated solution. In this solution dissolve 2-1/2 grains of iodide of
potassium, then add 1 ounce of collodion, and shake well. Let it settle
clear and decant for use.

The solution must be decanted every day. In order to make the most
sensitive collodion, I dissolve the bromide and iodide of potassium and
the collodion[G] in a saturated solution of carbonate of ammonia in water.
In using this collodion, pour it upon a clean glass plate to form a film
in the usual way, and as soon as the collodion has set, and before it
becomes dry, immerse the plate in a bath of nitrate of silver, made with
30 grains of nitrate of silver, 2 grains of iodide of silver, and 1 ounce
water. Take the plate directly from the bath to the camera, and after
sufficient exposure, the plate is taken to a dark room to develope the
impression with the following solution: 'Take pyrogallic acid, 4 grains;
acetic acid, No. 8, 1 ounce; dissolve and filter. For use, take of this
liquid 1-1/2 drachms, diluted with 6-1/2 drachms of water, and when the
impression is sufficiently developed, pour off the liquid, and immerse the
plate in a solution of the hyposulphite of soda, 4 ounces to the pint of
water. Wash the plate with pure water, and dry it in the usual way.

[Footnote G: This is a mistake: the collodion is not to be dissolved in
the "carbonate of ammonia in water," but only the bromide and iodide of
potassium. I called Mr. Cutting's attention to this, and he said I was
correct.--S. D. H.]

The advantages of the above process are, the brief time required to
produce an impression, and the sharpness of the pictures. Portraits can be
taken with as much facility as with the Daguerreotype, and the pictures
are sharp and of excellent tone. The impression thus obtained is negative,
and the positive picture is produced in the usual way. I denominate this
the mezzographic process.

What I claim as my improvements in the process of obtaining photographic
pictures, are--

_First._ Displacing the water from the cotton, for this purpose, with
strong alcohol, as set forth. I do not claim the use of alcohol as a
desiccating agent, but limit my claim to its special use and purpose, as
herein stated.

_Second._ The employment of bromide of potassium in combination with
collodion.

                                                James A. Cutting.

  T. Campbell,  } _Witnesses._
  Samuel Grubb. }

  _Dated July 11th, 1854._

       *       *       *       *       *

PATENT FOR THE USE OF JAPANNED SURFACES PREVIOUSLY PREPARED UPON IRON OR
OTHER METALLIC OR MINERAL SHEETS OR PLATES IN THE COLLODION PROCESS.

_To all whom it may concern:_

Be it known that I, Hamilton L. Smith, of Gambier, in the County of Knox,
and State of Ohio, have invented certain new and useful improvements in
Photographic Pictures, and I do hereby declare the following to be a full,
clear, and exact description of the same, and of the manner of making and
using my invention or discovery.

The nature of my invention or discovery relates to the taking of
_positive_ pictures by the photographic process, upon a black japanned
surface prepared upon iron or any other metallic plates or sheets, and
consists in the use of collodion, and a solution of a salt of silver, and
an ordinary camera.

To enable others skilled in the art to make and use my invention. I
will proceed to describe the manner of preparing and applying it which
I have found to answer well in practice; not confining myself, however,
to the special process or processes herein described, so long as the
characteristics of the invention remain the same.

I first take metallic sheets, preferring for the purpose iron, as this
metal is the only one, except the precious metals, which is without action
on the silver salts generally used, as also the other chemicals; but other
metallic or mineral sheets may be used, and I do not, therefore, confine
myself specially to any particular metal. Upon each of the sheets is
prepared a black japanned or varnished surface, such as is used by tinners
or japanners for coating metallic and other surfaces. The japan or varnish
may be made and applied as follows:--Take one quart of raw linseed oil;
add to this two ounces of asphaltum and sufficient umber, or lamp black,
to give the desired shade. Boil these ingredients until a portion dropped
on a cool surface will remain in a round spot without flowing away. It
is then thick enough to use. If it should be too thick, it can readily
be thinned with spirits of turpentine. Apply the japan to the sheets or
plates with a brush, and after allowing it to stand a short time, until
the marks of the brush disappear, place the sheets or plates in a drying
oven and submit them to heat until the surface will bear the finger to be
drawn over it without bringing off the japan; it may, if found necessary,
be coated again and treated in a similar way, and finally polished with
rotten-stone and oil, or other polishing material. Other ingredients may
be used in making the japan, such as mastic, lac or copal varnish, and
other shades of coloring matter may be used.

By collodion I mean any solution of gun-cotton or pyroxyline; and by a
solution of salt of silver, I mean any of the salts thereof which can be
used in photography for obtaining positive impressions by a camera.

A japanned surface may be prepared on glass, or on leather and other
fibrous materials. Or glass may be made black by means of coloring
matter introduced or embodied with the glass, so as to be _in_ instead
of _on_ the glass. But foreseeing the difficulty of embracing all
these applications in one application, I do not desire to have them so
considered; but reserve the right to hereafter apply for such application
of my general principle as I may deem essential, or of sufficient
importance to be protected by Letters Patent. And it might be proper to
add, that vulcanized gutta-percha or indurated rubber may be used as
the basis upon which, or in which the japanned surface may be made. The
invention, however, consists mainly on the surface, so that a silver
picture may be made upon it, said surface forming the background of the
picture.

The ingredients for fixing and developing the positive impression, upon
the japanned surface may be the same as those heretofore essayed by me in
a former application, and need not again be repeated here. Though other
chemicals, or other proportions of the same chemicals, may be used.

Having thus fully described the nature of my improvement in photographic
pictures, and shown how the same may be accomplished, what I claim therein
as new and desire to secure by Letters Patent, is:--

The obtaining _positive_ impressions upon a japanned surface previously
prepared upon an iron or other metallic or mineral sheet or plate, by
means of collodion and a solution of a salt of silver and a camera,
substantially as herein described.

                                                Hamilton L. Smith.

  Geo. T. Chapman. } _Witnesses._
  James H. Lee.    }

  _Dated February, 19th, 1856._

         *       *       *       *       *

PHOTOGRAPHIC PICTURES ON OIL.

_To all whom it may concern:_

Be it known that I, Joel Haywood Tatum, of the City of Baltimore and State
of Maryland, have discovered or invented a new and useful preparation of
oil ground or body, and mode of preparing the same by which Photographic
impressions, such as portraits of all sizes, landscapes or still life may
be produced upon such oil prepared ground body or surface, whether upon
canvass, mill-board, pannel, or other body whatever, without any permanent
injury to such body, ground or surface for the reception of colors in
oil (water) or dry (paste), without impairing the texture, quality,
durability, or other desirable quality of the body ground, or surface
rendered so impressible, and give the following as the Process used in
accomplishing the result.

I take ordinary prepared canvass, mill-board, pannel or other substance
for the reception of oil painting by any composition of oil (or oleaginous
substance) and oxide of lead or zinc, Spanish whiting, Fuller's earth, or
their equivalents, singly or in combination, and after having removed all
irregularities or lumps from the surface I damp or wet the surface with
spirits of wine, and wipe clean; after which, I treat the surface with a
solution of potassium or any good alkali, regulating the strength to the
amount of oil in the body-ground or surface to be treated (ordinarily 1
oz. of super, carb. soda to 1 pint of water), as soon as the surface has
uniformly changed color allow the surplus solution to run off, wash off
by pouring over the surface clean water, let dry, but not by the fire or
in the sun, as that would bring out the oil to the surface. When dry,
treat the surface again with a solution of the chloride of sodium (of
the strength ordinarily used and prescribed for paper positives), decant
from the surface the superfluous fluid after a minute, and let dry, as
before; remove to a dark room, and treat the surface with a solution
of the nitrate of silver, its strength being governed by the strength
of impression desired, usually 18 grains of nitrate of silver to 1 oz.
of distilled water; allow the solution to float upon the surface a few
moments to insure uniformity of deposit, and then decant the surplus,
in the bottle or lath; place a small piece of filtering paper on the
edge of the body, and place that, edge down, to facilitate the drainage;
when dry, place the negative impression (which must previously have been
obtained, by the use of the camera, either on collodion or albumen upon
glass or upon paper) upon the body or ground to receive the impression in
the position the picture is desired, with the face of the negative to the
surface of the body to receive the impression. If the negative impression
does not cover the whole surface, then a mat should be used so as to
extend to the edge of the ground on all sides. Expose to the light, and,
when sufficiently long, remove the negative into a dark room (lighted with
a feeble lamp); dash over the impression a weak solution of hyposulphite
of soda, and let stand a few moments; then wash off with a very dilute
acid of only sufficient strength to neutralize the alkalies remaining upon
the surface, usually five or six drops of sulphuric acid to an oz. of
water is sufficient.

What I claim as my own invention and discovery, and desire to secure by
Letters Patent, is the mode of preparing and rendering oil (oroleaginous)
bodies, grounds, or surfaces impressible or sensitive to the Photographic
art by the temporary destruction or chemical change of the oil or
oleaginous matter of the immediate surface only, by the use of spirits of
wine and alkaline solution, or their equivalents, and, after fixing the
impression by the use of hyposulphate of soda, the use of dilute acid, by
which last application the alkalies are neutralized and the oil restored
with the impression permanent upon the surface.

Disclaiming everything heretofore known in the production of Photographic
pictures upon paper or any unoiled body or surface.

                                                Joel Haywood Tatum.

  _Witnesses._

  J. S. Hollingshead, }
  E. G. Handy.        }

  Original, _dated April, 15. 1856_.
  Re-issue, _dated May 13, 1856_.

       *       *       *       *       *

PATENT FOR MAKING THE BORDER OF THE PICTURE TRANSPARENT, AND PLACING THE
MAT BACK OF THE PICTURE.

_To all whom it may concern:_

Be it known that we, Albert Bisbee, of Columbus, in the County of Franklin
and State of Ohio, and Y. Day, of Nashville, in the County of Davidson
and State of Tennessee, have invented certain new and useful improvements
in photographic pictures on glass, and we do hereby declare the following
to be a full, clear and exact description of the same.

The nature of our invention consists in making the edges of the coating
or film on the glass transparent so that the picture is made only on the
central part of the glass, and extending so far as to meet the inside edge
of the mat or border, generally used in putting up such pictures, and then
placing the mat back of the picture.

To enable others skilled in the art to make and use our invention, we will
proceed to describe the same as follows:--

We place inside of the camera, and about one-tenth of the focal distance
of the lens from the glass, a board having an aperture of any desired
pattern that we wish the edges to have. This board shades the edges of
the glass, thereby leaving them transparent in the picture. Then the
picture, being taken in the usual manner, is finished by varnishing with
transparent white varnish, and then backed with japan varnish, care being
taken to have the japan on the back extend only to meet the inside edges
of the mat. Then we place the mat back of the picture and secure it in its
place with the preserver.

If applied to the process, as patented by J. A. Cutting, with two glasses,
the picture is made as above described, and then the second glass is
applied, and finished as before by backing with japan.

The advantage of our improvement, is in having the mat protected from
being soiled, and making the picture appear more round, causing an
illusion as though the picture or image was suspended in the atmosphere,
clear from the background.

Having thus fully described the nature of our invention, what we claim
therein as new, and desire to secure by Letters Patent, is, making the
border of the picture transparent and placing the mat back of the picture,
as described in the above specification, and for the purpose set forth.

  _Witnesses to the signature of A. Bisbee._

  C. A. Barker,  }
  Wm. Field.     }                                  A. Bisbee.

  _Witnesses to the signature of Y. Day._

  B. Bingham,    }
  W. Atkins.     }                                  Y. Day.

  _Dated May 27th, 1856._

       *       *       *       *       *


PATENT FOR THE APPLICATION OF COLORING SUBSTANCES, OR MATTER, TO
PHOTOGRAPHIC IMPRESSIONS.

Be it known that I, Giles Langdell, and Marcus A. Root, of Philadelphia,
in the State of Pennsylvania, have invented a new and improved mode of
coloring daguerreotype and other photographic portraits or pictures made
on glass, metal or other material; and we do hereby declare that the
following is a full and exact description:--

The nature of our invention or discovery consists in providing and
applying both mineral and vegetable coloring matters in solution to the
daguerreotype or any other photographic impression, introducing the said
coloring matter either into the collodion or the developer, or by pouring
upon the plate after the impression is fixed by hyposulphite of soda, or
the cyanide of potassium, or by any other means.

The several coloring substances, E. G. red saunders, alkanet, dragons'
blood, &c., &c., can be used separately or in conjunction or compounded
with various mineral substances, or with any coloring matters obtained
from other roots, woods, gums or other vegetable matter, the proportions
or quantity employed being varied or regulated by the lightness or depth
and strength of tone which may, from time to time, be required.

The desired or similar results may be obtained from different formulæ.
The following answers for all practical purposes, but may be varied at
pleasure:--

Digest for two or three days red saunders (pterocarpus santalinus) half a
pound in three pints of water to which the aqua-ammonia has been added.
Then pour off the solution and precipitate by the addition of nitric acid.
Wash the precipitate thoroughly with water and dry it. Then dissolve it in
strong alcohol and dilute with the same as required to produce the tone or
tint that may be desired. Alkanet (anchusa tinctoria) may be prepared in
the same way. Dragons' blood dissolved in alcohol and treated in the same
manner will produce the various shades of yellow. The foregoing articles,
and also madder, indigo, cochineal, and some other coloring substances
both vegetable and mineral alone or combined, will produce pleasing
results when applied as follows (although they may be introduced into the
collodion):--

We prefer first to develope the impression, then to fix and dry it, and
afterwards to flow on the toning or tinting solution, as collodion or
varnish, &c., is poured upon the plate, allowing the solution to run off
the corner, and then levelling the plate to make the fluid flow uniformly
over and tint the whole surface of the plate evenly.

Then wash at once and thoroughly with clean water, and stand the plate
up to dry, after which it may be colored (the dress of any tint or color
desired--the face, hands, &c., are flesh tint) with dry colors (as is
usual in coloring daguerreotypes) applied to the collodion or upon the
varnish.

What we claim as our invention and discovery, and desire to secure by
Letters Patent, is the application of coloring substances or matter
to Photographic impressions or pictures upon glass or metal, or other
material in the form and manner herein described.

  _Witnesses._

  James J. B. Ogle, }                             Giles Langdell [L. S.]
  Williams Ogle,    }                             M. A. Root. [L. S.]

  _Dated July 15th, 1856._

       *       *       *       *       *

PATENT FOR THE USE OF ALBUMENIZED COLLODION.

_To all whom it may concern:_

Be it remembered, that I, Victor M. Griswold, of the City of Lancaster,
in the County of Fairfield and State of Ohio, have invented certain
improvements in the art and mode of taking Photographic Pictures, and I do
hereby declare that the following is a full and exact description thereof:

The nature of my invention consists in an improvement in the photographic
art of taking pictures. To one quart of collodion prepared in the usual
way or manner, I add three ounces of a solution prepared thus: The clear
solution which results from the whites of eggs which have been well
beaten, and one equal bulk of pure soft water. When this is added to the
collodion, it is thrown to the bottom in long stringy white masses, which
after a few days impart to the liquid albuminous properties, rendering
the film closer in texture, and bringing out all the minor details more
sharply and perfectly than by the ordinary collodion, and giving to the
picture a glossy and sparkling tone, unlike any produced by other means.

Another method which I frequently adopt is thus; albumen as above, without
water, to which is added iodide of potassium forty grains; this throws
down the albumen in jelly-like masses, and, when added to the collodion,
not only iodizes it, but produces the same effect upon the collodion as by
the formula above. Also, another method: one ounce of chloroform, to which
is added one half ounce of albumen, prepared as above, iodized; this forms
also a soft semi-transparent jelly, which on being added to the collodion
produces perhaps the best effect of any of these preparations.

This addition of albumen also answers a far better purpose, than any that
has hitherto been employed for freeing old samples of collodion from free
iodine held in suspension by which they can be rendered as clear and
limpid as they were when first mixed.

What I claim as my invention, and desire to secure by Letters Patent is
the addition of albumen to collodion in the manner and for the purpose
herein and above specified.

                                               V. M. Griswold.

  Alfred M'Veigh,  } _Witnesses._
  J. C. Heuley.    }

  _Patented July 15th, 1856._

       *       *       *       *       *

COLORING AMBROTYPES.

_To all whom it may concern:_

Be it known that we, D. B. Spooner and H. B. Spooner, of Springfield, in
the County of Hampden, in the State of Massachusetts, having invented new
and useful improvements in coloring Ambrotype or Photographic Pictures on
glass, and we do hereby declare that the following is a full and exact
description thereof:--

The nature of our invention consists, in so preparing the collodion film
containing the picture in alternate placers with gum or other suitable
material, so that when a penetrating dye or pigment, in a solution that
will penetrate the collodion film, may be deposited on any particular
portion of the picture between the collodion film and the glass, in order
to give it the requisite color properly distributed between the face,
drapery, &c.

The following is the process adopted:--

After the picture is thoroughly washed and dried, proceed with a brush to
cover any portion of the picture not designed to take the color, with a
solution of gum or any other substance insoluble in the coloring solution,
but soluble in any other liquid in which the coloring matter is not
soluble.

E. G.--Take a solution of gum arabic in water, and apply it to a portion
of the picture. Now take a solution of turmeric in alcohol, and pour it
upon the collodion surface of the picture, and you immediately get a
deposit of the coloring matter between the collodion and the glass, the
portion of the picture covered with the gum not being penetrated by the
alcohol, is protected from the color while all other portions are colored.

Then, by washing the picture in water, the gum is dissolved and washed
off, and the parts uncolored may remain in their natural state without
color, or, by applying the gum solution to the portion already colored
with a part of the uncolored portion, another color may be produced by the
use of another pigment in the same manner as before described.

In this manner any number of colors may be produced; or, when a small
portion only of the picture is to be colored, the whole of the picture
may be colored and dried, and then that portion which is to retain the
color may be covered with the gum solution, and the coloring matter not
protected by the gum may be extracted with alcohol or other solvent, and
the gum washed off as before.

The advantages of our invention consist in depositing the coloring matter
in its _various tints_ on the front side of the picture between the
collodion and the glass, instead of coloring the fibre of the collodion,
or the upper side of it, as is common, which does not show through to
the positive side of the picture on account of the opacity of the silver
deposit which forms the picture.

We do not claim the coloring of a picture all over with a single tint, but

What we claim as our invention and desire to secure by Letters Patent, is
the application of gum arabic or other equivalent material, as set forth
in the specification, for the purposes therein described, and no other.

                                         D. B. Spooner.
                                         H. B. Spooner.

  _Witnesses._

  George W. Adams, }
  Chas. H. Codman. }

  _Patented August 5, 1856._



CHAPTER VIII.


=THE COLLODIO-ALBUMEN PROCESS.=

[Sidenote: COLLODIO-ALBUMEN PROCESS.]

This is a process, invented by Dr. Taupenot, for obtaining negatives on
glass, which bids fair to outrival all others, being easy of manipulation,
and giving results of the most exquisite minutiæ and beauty. Glass
plates, when prepared and excited by this process, may be kept at least
a fortnight before being developed, and these plates when exposed in the
frame may be developed immediately, or kept for days before commencing
this operation. Indeed it is quite possible to prepare and excite a number
of plates before leaving home to go on a tour of twelve or fourteen days;
to expose the plates at any time or place during the journey, and bring
them home to be developed.

The manipulation may be said to consist of nine distinct operations.

1. Cleaning the plate. 2. Coating with iodized collodion. 3. Exciting the
collodion film. 4. Coating with albumen. 5. Exciting the albumen coating.
6. Exposure in the camera. 7. Developing the image. 8. Fixing the image.
9. Varnishing the plate.

Before describing these operations, I propose to give clear directions for
preparing the necessary solutions, merely promising that, where I have
deviated from the inventor's plan, it has been after performing careful
experiments, to test the merits of the two modes of proceeding.

The necessary solutions for this process are:

Collodion bath solution. Iodized collodion. Iodized albumen. Albumen bath
solution. Pyrogallic solution. Silver developing solution. Fixing solution.


_Collodion Bath Solution._

  Nitrate of silver in crystals                       1 ounce.
  Iodide of potassium                                 2 grains.
  Distilled water                                    16 ounces.
  Alcohol                                             2 drachms.

Dissolve the ounce of nitrate of silver in two ounces of the distilled
water, and the two grains of iodide of potassium in one drachm of
distilled water; mix the two solutions and shake well together until the
precipitate which is first thrown down is re-dissolved; when this takes
place, add the remaining fourteen ounces of distilled water, and the two
drachms of alcohol. On the addition of the water a turbidness ensues,
which must be removed by the solution being very carefully filtered
through filtering paper; and the filtered liquid should be clear and
transparent, free from any deposit or floating particles, and must possess
a slightly acid reaction of test-paper.

In order to ascertain if the solution thus prepared possesses the
necessary amount of free acid without superabundance, proceed to test and
to correct it, if necessary.


_Iodized Collodion,_

The collodion to be used in this process must be one yielding good
_negative_ pictures--that supplied by Home & Thornthwaite under the name
of negative collodion answers admirably. This is supplied either ready
iodized, or the collodion and iodizing in separate bottles. As this
collodion becomes less sensitive after being iodized a fortnight, it is
advisable to iodize no more than will be used in that time--therefore,
obtain the collodion and the iodizing solution separate, as the mode of
iodizing this collodion is very simple. Half an ounce of the iodizing
solution is mixed with one ounce and a half of collodion, and the mixture
allowed to settle twelve hours before being used; and it is even advisable
to pour off the clear solution into a perfectly clean bottle, in order to
get rid of any insoluble matter which may fall to the bottom.


_Iodized Albumen._

  White of egg (free from yelk)                      10 ounces.
  Honey                                               1 ounce.
  Iodide of calcium                                   2 scruples.
  Yeast                                               1 tablespoonful.

Mix these together in a tall glass jar, or wide-mouthed bottle of at least
one pint capacity; tie a piece of paper, pierce with small holes over the
top to keep out dust; then place the whole near a fire or other warm
situation, where the temperature is not lower than seventy degrees, or
higher than ninety degrees. In a few hours fermentation commences, which
is evident by the formation of bubbles of gas, rising through the liquid.
This action continues for five or six days; when it ceases, pour the whole
on a paper-filter contained in a funnel, underneath which must be placed
a bottle to receive the liquid as it passes through. The fluid being of a
viscid nature filters slowly, generally occupying twelve hours.

The filtered liquid is the "iodized albumen," which is said by Dr.
Taupenot to keep good for years. It must be carefully preserved from dust
or contact with any substance, as the success of the picture depends
materially on the condition of this albumen.


_Albumen Bath Solution._

  Nitrate of silver                                   1 ounce and a half.
  Acetic acid, glacial                                1 ounce.
  Distilled water                                    16 ounces.
  Animal charcoal                                     2 drachms.

Dissolve the nitrate of silver in the distilled water, then add the acetic
acid and animal charcoal, and keep in a closely stoppered bottle for use.


_Pyrogallic Solution._

  Pyrogallic acid                                    15 grains.
  Glacial acetic acid                                 2 drachms.
  Alcohol                                             2 drachms.
  Distilled water                                     7 ounces.

Dissolve the pyrogallic acid in the distilled water, and then add the
acetic acid and alcohol.


_Silver Developing Solution._

  Nitrate of silver                                   1 drachm.
  Acetic acid                                         2 drachms.
  Distilled water                                     7 ounces.

Dissolve the nitrate of silver in the distilled water, and then add the
acetic acid.


_Fixing Solution._

  Hyposulphite of soda                                2 ounces.
  Water                                               1 pint--dissolve.


_Varnish._

The varnish best adapted for this purpose is that supplied by Home &
Thornthwaite, and termed negative varnish.[H]

[Footnote H: In this country, Humphrey's Collodion Gilding is the article
in almost universal use.]


_Cleaning the Plate._

The plates must be cleaned in the usual way, merely premising that
extra care must be observed to remove every impurity, as cleanliness in
photography is an absolute necessity.

In order to hold large plates whilst being cleaned, the "screw
plate-holder" is exceedingly useful. This is made in three sizes, and
adapts itself to all sized plates.

The small size is useful for plates up to 7 inches by 6.

The second size is for plates up to 10 inches by 8.

And the third size for plates up to 14 inches by 10.


_Coating with Iodized Collodion._

The plate having been thoroughly cleaned, and received its final polish by
the use of a prepared chamois leather, is coated with negative collodion,
which has been iodized at least twelve hours, and allowed to settle.


_Exciting the Collodion Film._[I]

[Footnote I: This and subsequent operations (except exposure in the
camera) must be performed in a dark room.]

After the ether has evaporated, and the surface of the collodion appears
set, the plate must be laid, collodion side upwards, on a glass dipper,
and plunged with _one downward movement_ into a bath filled to within an
inch of the top with collodion bath solution, made as described at page
190, which must be carefully filtered through filtering paper before
being used. After the plate has been allowed to remain in the bath one
minute, it is lifted out three or four times, in order to facilitate the
removal of the oily appearance the plate now presents. When the surface
appears wetted uniformly, on being drawn out of the solution the plate is
removed from the dipper, and the excess of solution drained off, and is
then placed collodion side upwards, on a fixing stand, and distilled or
filtered rain water poured over the surface, so as to remove as much as
possible of the bath solution from the surface. The plate is now removed
from the fixing stand; the back well washed with water, and then placed
nearly upright on blotting paper, with the face against a wall for _one
minute_ to drain.


_Coating with Albumen._

Having allowed the plate to drain one minute, place it again on a
levelling stand, with the film upwards, and pour over it as much of the
iodized albumen as the plate will hold, from a glass measure containing
not more than enough of the albumen to coat two plates with, pour off the
excess into the measure, and again cover the plate with albumen three
separate times; ultimately drain off as much as possible of the excess of
albumen, and place the plate nearly upright against the wall, with the
coated side inwards, to dry, which takes place in an ordinary temperature
in about one hour.

In coating with albumen, the presence of air-bubbles or dust must be
guarded against. The former can be easily done by taking care, in pouring
the albumen into the measure and on the plate, not to pour so as to
generate air-bubbles in the liquid. But should any be detected, hold the
plate horizontally and give it another coating of albumen, then incline
the plate so that the bulk of the liquid shall pass over and carry off the
bubbles with the running stream. Dust on the plate must be prevented by
operating in a room as free from this photographic enemy as possible.

In order to render the coating of albumen as uniform as possible, the
plate must stand to dry on two or three layers of filtering paper and
the upper surface must touch the wall at _one point only_ and not to be
allowed to rest against it along its entire upper edge.

When the albumen coating is _thoroughly dry_ (and not till then), the
plate is ready to be excited, but if more have been prepared than are
likely to be used for taking pictures on during the next ten days or
fortnight, they may be stowed away in a plate box, ready to receive the
sensitive coating at any time. The author's experience has led him to
believe that these albumenized plates will keep good any length of time,
as plates which had been coated a month, when excited, exposed, and
developed, appeared to possess all the properties of recently prepared
plates.


_Exciting the Albumen Coating._

Prior to the plates being excited they must be _thoroughly dry_ and free
from any particles of loose dust on the surface, back, or edge. Sufficient
of the albumen bath solution, page 192, must be filtered through filtering
paper to fill a dipping bath of the required size, so that the plate can
be immersed in it.

The careful filtering of the fluid is very necessary in order to free it
from any floating particles, and to separate the animal charcoal.

The plate is now taken and laid, albumen side upwards, on the dipper, and
then lowered into the bath with one steady downward movement, where it is
allowed to remain one minute; it is then taken out, the excess of liquid
drained off, and placed on the fixing stand, with the albumen surface
uppermost, and a stream of water poured over it for at least one minute,
so as to remove every particle of the bath solution. This complete washing
is very necessary, in order to prevent stains in the after development,
which invariably takes place around the edges, if not thoroughly washed.
The plate having been thoroughly washed, is leaned against a wall to dry,
or if required for immediate exposure, may be dried on a plate of heated
metal or foot warmer, but in no case must the exposure in the camera take
place until the surface is thoroughly dry.


_Exposure in the Camera._[J]

[Footnote J: Remarks as to the selection of the view, &c., are not given,
as this can be effected by the individual taste of the operator, but care
must be taken that direct rays from the sun shall not fall on the lens or
enter the camera during the exposure of a plate.]

As has been before stated, this operation may take place immediately the
plate is thoroughly dry after being excited, or a fortnight may intervene
between the excitement and exposure, provided the plate is kept very
carefully excluded from light and any chemical or sulphurous vapors, in a
plate-box adapted for that purpose, with the sensitive surface towards the
back of the box. When the exposure is about to take place, or at any time
previously, the camera-backs may each have a plate placed in them ready
for exposure; to do this, the camera-back must be taken into the operating
room and the door closed, so as to exclude all white light. The hinged
flap of the camera back is opened, and the prepared plate laid, with its
sensitive surface downwards, or next the sliding flap, so that its corners
may rest on the silver wire corners of the plate frame previously placed
within the camera back ready to receive it. The hinged flap is now closed
and kept from opening by turning the flap button over it; the sliding
flap is examined to see that it is pushed closely down so as to guard any
access of light, and it is then ready to be placed in the camera, and
may be taken into the open air with impunity. Should the exposure not
take place immediately, or, should the camera back have to be carried any
distance, it is advisable either to wrap it up in black cloth, or secure
the flaps from the chance of coming open during transit, by a stout string
being tied around the back.

The focussing is conducted in the usual way and the cap replaced on the
lens; the focussing glass is now removed and the camera back fitted into
the same aperture, with the sliding flap next the lens. The sliding flap
is pulled up to its fullest extent, placing the hand on the camera back to
prevent it rising out of the camera with this action. The cap of the lens
is then removed, so that the light may be admitted into the camera, and
to fall on the sensitive surface of the plate. After the necessary time
of exposure has taken place, the cap is replaced on the lens, the sliding
flap is pushed down, and the camera back withdrawn from the camera; the
plate can then be taken into the operating room to be developed, or this
operation may be deferred for days or even a week, or more if convenient.
The time of exposure in the camera varies according to the intensity of
the light and the aperture and focal length of the lens; therefore, to
give the exact time of exposure would be impossible, still it may assist
the amateur if I give the time required in summer with full sunshine, and
merely state that this time may be increased to double in winter or dull
weather.

In the ordinary sunshine of a summer's day the time of exposure will be:

  30 seconds with a lens of 4-inch focus and 1/2-inch stop.
  21 seconds with a lens of 4-inch focus and 5/8-inch stop.
  5 seconds with a lens of 4-inch focus and 1-1/4 inch aperture
    with no stop.
  1-1/2 minute with a lens of 6-inch focus and 1/2-inch stop.
  4-1/2 seconds with a lens of 6-inch focus and 2-1/4-inch aperture
    with no stop.
  2 minutes with a lens of 8-inch focus and 1/2-inch stop.
  1-1/4 minute with a lens of 8-inch focus and 5/8-inch stop.
  3-1/4 minutes with a lens of 10-inch focus and 1/2-inch stop.
  2 minutes with a lens of 10-inch focus and 5/8-inch stop.
  5 seconds with a lens of 10-inch focus, 3-1/4-inch aperture,
    with no stop.
  6-1/4 minutes with a lens of 14-inch focus and 1/2-inch stop.
  4 minutes with a lens of 14-inch focus and 5/8-inch stop.
  2-1/4 minutes with a lens of 14-inch focus and 3/4-inch stop.
  8-1/4 minutes with a lens of 16-inch focus and 1/2-inch stop.
  5-1/4 minutes with a lens of 16-inch focus and 5/8-inch stop.
  2-1/4 minutes with a lens of 16-inch focus and 3/4-inch stop.


_Developing the Image._

The camera back is taken into the operating room, from which all white
light is carefully excluded, the plate removed from the camera back, and
laid, albumen side upwards, on the fixing stand; as much distilled water
is now poured on it as the surface will hold, taking care that every part
of the sensitive surface is covered with the liquid; allow the water to
remain on the surface for one minute, then pour off and drain slightly;
replace the plate on the stand, and pour over the surface so as thoroughly
to cover every part, the pyrogallic solution (made as described at page
192, and carefully filtered just before being used); allow this to remain
on the plate for one minute, then drain off into a perfectly clean
measure, and add to it an equal bulk of silver developing solution, page
192; mix these thoroughly together with a glass rod, and then pour the
mixed liquids over the plate; allow them to rest until the picture begins
to appear, which generally takes about from three to five minutes; then
pour off and on repeatedly, until the developing fluid becomes opaque,
which then contains floating particles, and these, if allowed to do so,
would settle on the plate, to the injury of the picture; but this may be
prevented by brushing the surface with a camel's-hair brush frequently
during the development. When this opacity of the developing fluid takes
place, drain all the fluid off the plate, and thoroughly wash with water;
then mix another quantity of pyrogallic and silver developing solution
in the same proportions as before, and pour this on and off the plate as
before, until the picture appears sufficiently intense, and the middle
shades well brought out; when this takes place drain off, and wash with
water, so as to clean the surface thoroughly, and the plate is then ready
for the next step, "fixing the image."

Should the picture begin to develope in less than three minutes after the
application of the mixed developing fluids, thoroughly drain the plate,
and wash well with water, then continue the development with a solution of
three parts pyrogallic solution and one part silver developing solution;
but should the picture not begin to appear in five minutes, the addition
of half a drachm of the albumen bath solution to each ounce of mixed
developing solution will be necessary, in order to obtain the middle
shades and the required intensity. It may be stated, as a guide, that the
best negatives which the author has produced occupied from ten to twelve
minutes in developing.


_Fixing the Image._

The plate, having been thoroughly freed from the developing fluid by
careful washing, is now placed on the fixing stand, and the surface
covered by the fixing solution, made as described at page 192, being
poured over it. In a few seconds the yellow opalescent color of the film
will begin to disappear, and its complete removal may be hastened by
blowing gently on the plate, so as to disturb the fluid.

When every particle of yellowness has disappeared, the fixing solution is
drained off, and the surface _thoroughly_ washed, and it is then leaned
against the wall to drain and dry.


_Varnishing the Plate._

The plate, being thoroughly dry, is ready to receive a coating of
transparent varnish.[K] in order to protect the albumen surface from
injury during the printing process. To do this effectually the plate must
be held before a fire, or over a lamp, until it is slightly warm all over;
then pour over its surface the negative varnish, in the same manner as
collodion is applied; allow the superfluous varnish to drain back into the
bottle; hold the plate again before the fire until the whole of the spirit
is evaporated; and, when cold, the plate is ready to be printed from, so
as to produce any number of positive pictures on paper.

[Footnote K: Humphrey's Collodion Gilding is the best for this purpose.]

It will be observed, that in describing this process, the operator has
been supposed to be so situated, that in case a second view of the same
spot were required, he could return to his operating room, remove the
plate which had been exposed, from the camera back to the plate box,
and place another in the camera back, ready for taking another view.
But, unfortunately, this is not at all times practicable. We, therefore,
require some means of removing the plates, after being exposed, from the
camera back into the plate box, and substituting others in their stead,
whilst we are in the open air.

In order to effect this, the "field plate box" has been devised by the
author, by the aid of which the plates may be removed from the box,
exposed in the camera, and again returned into the box, without any
possibility of access of light falling on it.

This box is but a trifle larger than the ordinary one, and is furnished
with two sliding bottoms, working in grooves, one over the other; the
lower bottom has a grooved channel, into which the side of the camera
back slides; the camera back has an aperture through the side, closed by
a narrow slide, and the lower bottom of the field box has a corresponding
one. We now suppose the field box to have been previously filled with
excited glass plates, having their sensitive sides towards the back of the
box, and the box lid closed. The bottom slide is now pushed on until the
aperture is in a line with any particular groove of the field box (which
position is indicated by a numbered scale and index point). The camera
back is then slid on to its place on the field box, so that the hinged
flap is towards the front of the box, and its narrow slide drawn out. The
upper slide is then withdrawn, and the box inclined, so that the plate in
that groove opposite the aperture in the lower slide, may pass through
into the camera back. When this has taken place, push in the narrow slide
of the camera back, invert the box, and push in the inner slide; then
withdraw the camera back from its channel, and expose the plate in the
camera. When this is done, slide the back again into its channel, draw out
the inner box slide, then the narrow camera back slide, invert the box,
and the plate will then leave the camera back and pass into the field box,
occupying the same groove as before.

In order to get out another plate, slide the lower bottom, so that the
index points to the number on the scale, as that of the groove in which
the required plate is situate. Then proceed as before directed.



CHAPTER IX.


On a mode of Printing enlarged and reduced Positives, etc., from Collodion
Negatives.

To explain the manner in which a photograph may be enlarged or reduced in
the process of printing, it will be necessary to refer to the remarks made
at page 20, on the _conjugate foci_ of lenses.

If a collodion negative be placed at a certain distance in front of a
camera, and (by using a tube of black cloth) the light be admitted into
the dark chamber only through the negative, a reduced image will be formed
upon the ground glass; but if the negative be advanced nearer, the image
will increase in size, until it becomes first equal to, and then larger
than, the original negative; the focus becoming more and more distant from
the lens, or _receding_, as the negative is brought nearer.

Again, if a negative portrait be placed in the camera slide, and if
the instrument be carried into a dark room, a hole be cut in the
window-shutter so as to admit light through the negative, the luminous
rays, after refraction by the lens, will form an image of the exact size
of life upon a white screen placed in the position originally occupied
by the sitter. These two planes, in fact, that of the object and of the
image, are strictly _conjugate foci_, and, as regards the result, it is
immaterial from which of the two, anterior or posterior, the rays of light
proceed.

Therefore in order to obtain a reduced or enlarged copy of a negative, it
is necessary only to form an image of the size required, and to project
the image upon a sensitive surface either of collodion or paper.

A good arrangement for this purpose may be made by taking an ordinary
portrait camera, and prolonging it in front by a deal box blackened inside
and with a double body, to admit of being lengthened out as required; or,
more simply, by adding a framework of wood covered in with black cloth. A
groove in front carries the negative, or receives the slide containing the
sensitive layer, as the case may be.

In reducing photographs, the negative is placed in front of the lens, in
the position ordinarily occupied by the object; but in making an enlarged
copy it must be fixed behind the lens, or, which is equivalent, the lens
must be turned round so that the rays of light, transmitted by the
negative, enter the back glass of the combination, and pass out at the
front. This point should be attended to in order to avoid indistinctness
of image from spherical aberration.

A portrait combination of lenses of 2-1/2 or 3-1/4 inches is the best form
to use, and the actinic and luminous foci should accurately correspond, as
any difference between them would be increased by enlarging. A stop of an
inch or an inch and a half aperture placed between the lenses obviates to
some extent the loss of sharp outline usually following enlargement of the
image.

The light may be admitted through the negative by pointing the camera
towards the sky; or direct sunlight may be used, thrown upon the negative
by a plane reflector. A common swing looking-glass, if clear and free from
specks, does very well; it should be so placed that the centre on which it
turns is on a level with the axis of the lens.

The best negatives for printing enlarged positives are those which are
distinct and clear; and it is important to use a small negative, which
strains the lens less and gives better results than one of larger size.
In printing by 2-1/4 lens for instance, prepare the negative upon a plate
about two inches square and afterwards enlarge it four diameters.

Paper containing chloride of silver is not sufficiently sensitive to
receive the image, and the print should be formed upon collodion, or on
iodized paper developed by gallic acid.

The exposure required will vary not only with the intensity of the light
and the sensibility of the surface used, but also with the degree of
reduction or enlargement of the image.

In printing upon collodion the resulting picture is positive by
transmitted light; it should be backed up with white varnish, and then
becomes positive by reflected light. The tone of the blacks is improved by
treating the plate first with bichloride of mercury, and then with ammonia.

Mr. Wenham, who has written a most practical paper on the mode of
obtaining positives of the life size, operates in the following way:--he
places the camera, with the slide containing the negative in a dark room,
and reflects the sunlight in through a hole in the shutter, so as to
pass first through the negative and then through the lens; the image is
received upon iodized paper, and developed by gallic acid.

_On Printing Collodion Transparencies for the Stereoscope._--This may
be done by using the camera to form an image of the negative in the
mode described at the last page; but more simply by the following
process:--Coat the glass, upon which the print is to be formed, with
collodio-iodide of silver in the usual way, then lay it upon a piece of
black cloth, collodion side uppermost, and place two strips of paper of
about the thickness of cardboard and one-fourth of an inch broad, along
the two opposite edges, to prevent the negative being soiled by contact
with the film. Both glasses must be perfectly flat, and even then it may
happen that the negative is unavoidably wetted; if so, wash it immediately
with water, and if it be properly varnished no harm will result.

A little ingenuity will suggest a simple framework of wood, on which the
negative and sensitive plate are retained, separated only by the thickness
of a sheet of paper; and the use of this will be better than holding the
combination in the hand.

The printing is conducted by the light of gas or of a camphine or
moderator lamp, diffused daylight would be too powerful.

The employment of a concave reflector, which maybe purchased for a few
shillings, ensures parallelism of rays, and is a great improvement.
The lamp is placed in the focus of the mirror, which may at once be
ascertained by moving it backwards and forwards until an _evenly
illuminated circle_ is thrown upon a white screen held in front. This in
fact is one of the disadvantages of printing by a naked flame--that the
light falls most powerfully upon the central part; and less so upon the
edges, of the negative.

       *       *       *       *       *

(From Humphrey's Journal, No. 17, Vol. 8.)

On the Use of Alcohol for Sensitizing Paper.

[Sidenote: TO SENSITIZE PAPER.]


I have practised for some time the following simple method, which appears
to me to be very superior for cleanliness and celerity in working, for
depth of tone, and especially for purity of white in its results. By means
of it T have produced very satisfactory results upon paper which was
otherwise nearly worthless.

To your sensitizing solution (which should be not less than 60 grains to
the ounce), whether simple nitrate or ammonio-nitrate, add 50 per cent, of
alcohol. Float the paper upon the solution for 40 seconds.

This method answers equally well for albumenized or plain paper.
You will find that the solution penetrates the paper which flattens
_instantaneously_ upon it. It becomes as transparent as though it were
oiled, and every minute air-bubble or defect in the paper is rendered
visible. Remove the air-bubbles by pressing upon the paper about an inch
from the bubble, and thus driving it out under the paper. In doing this,
if the solution flows partially over the back of the paper, shake it
until the paper is wholly immersed, which will prevent any unevenness
in printing. The paper reassumes its transparency in the toning bath,
but it will dry a pure white. The sensitising solution will not become
materially discolored even after frequent applications of albumenized
paper. Should it become so much discolored as to give a dark hue to the
paper, shake it in a bottle with two drachms Of animal charcoal and leave
it a night to settle. It will filter clear. A very small portion of your
solution may be made available in sensitizing a sheet of paper by pouring
it upon a clean glass, the size of the paper or a little larger, which
is carefully levelled and nicely laying down the paper upon it. This is
useful when your solution is too small to float in your trays. The alcohol
causes it to flow and be absorbed with perfect evenness.

To remove the papers from the solution and dry them:--Provide a dozen
or more clothes-pins, of the kind that are supplied with a ring of
india-rubber for a spring. Into the top drive a pin firmly and bend it
to a hook. Lift a corner of the paper by passing under it the point of a
quill tooth-pick, and attach to it one of the clothes-pins; lift the edge
out by this, and attach another to the other corner. You may thus carry
the sheet by the pins and hang it upon a line to dry without touching it
with the fingers, a matter of some importance to Amateurs of the art, who
must have unstained hands for their day's _business_.

It may be worth while here to add the following simple and economical
method of printing, which I have found to surpass in convenience and
afford all the advantages of the most expensive printing frames. Four
common clothes-pins, such as work with a _wire_ spring supply pressure
enough for a 4/4-plate. Lay your prepared paper upon the negative, and
next to it about twenty _separate leaves_ of thin common wrapping paper
cut to the size of the negative; next a sheet of tolerably stiff and
smooth writing paper, and lastly, a piece of glass as a back to the whole.
Let the glass back be pushed from the lower edge of the papers about 1/20
of an inch, or just so far as to enable you to pinch the negative and
papers with the thumb-nail and forefinger. Attach a pin to each corner
and your negative is prepared for exposure. Now, to examine your picture
without endangering its displacement:--remove the pins from one end, and
place it, face downwards, on a table, the other end with pins attached
projecting an inch beyond the edge. Hold down the back glass with the left
hand, while with the right you remove the pins and pinch the papers and
negative together between the forefinger and thumb-nail. Upon the smooth
sheet of paper you can easily slide the back glass an inch from the edge.
Hold it there, and on the uncovered margin attach _three_ of the pins with
as deep a bite as they will take. You may now examine your picture to
within an inch of its margin, as you would turn over the leaves of a book.
To replace the back, lay it again on the table and slide the back glass up
to the pins before you remove them. The rest of the process is obvious.

The minutiæ of my communication may excite a smile with some, but I shall
always act upon the principle, that nothing is more out of place than an
apology for minuteness in describing manipulations.

                                                     G. B. C.

       *       *       *       *       *

Recovery of Silver from waste Solutions,--from the black Deposit of Hypo
Baths, etc.

[Sidenote: RECOVERY OF WASTE SILVER, ETC.]


The manner for separating metallic silver from waste solutions varies
according to the presence or absence of alkaline hyposulphite and cyanides.

a. _Separation of metallic Silver from old Nitrate Baths._--The silver
contained in solutions of the nitrate, acetate, etc.; may easily be
precipitated by suspending a strip of sheet copper in the liquid; the
action is completed in two or three days, the whole of the nitric acid and
oxygen passing to the copper, and forming a blue solution of the nitrate
of copper. The metallic silver however separated in this manner, always
contains a portion of copper, and gives a blue solution when dissolved in
nitric acid.

A better process is to commence by precipitating the silver entirely in
the form of _chloride of silver_, by adding common salt until no further
milkiness can be produced. If the liquid is well stirred, the chloride of
silver sinks to the bottom, and may be washed by repeatedly filling the
vessel with common water, and pouring off the upper clear portion when
the clots have again settled down. The chloride of silver thus formed may
afterwards be reduced to metallic silver by a process which will presently
be described.

b. _Separation of Silver from solutions containing alkaline Hyposulphites,
Cyanides or Iodides._--In this case the silver cannot be precipitated by
adding chloride of sodium, since the chloride of silver is _soluble_ in
such liquids. Therefore it is necessary to use the sulphuretted hydrogen,
or the hydrosulphate of ammonia, and to separate the silver in the form of
_sulphuret_.

Sulphuretted hydrogen gas is readily prepared, by fitting a cork and
flexible tubing to the neck of a pint bottle, and having introduced
_sulphuret of iron_ (sold by operative chemists for the purpose), about as
much as will stand in the palm of the hand, pouring upon it 1-1/2 fluid
ounces of oil of vitriol diluted with 10 ounces of water. The gas is
generated gradually without the application of heat; and must be allowed
to bubble up through the liquid from which the silver is to be separated.
The smell of sulphuretted hydrogen being offensive, and highly poisonous
if inhaled in a concentrated form, the operation must be carried on in the
open air, or in a place where the fumes may escape without doing injury.

When the liquid begins to acquire a strong and persistent odor of
sulphuretted hydrogen, the precipitation of sulphuret is completed. The
black mass must therefore be collected upon a filter, and washed by
pouring water over it, until the liquid which runs through gives little or
no precipitation with a drop of nitrate of silver.

The silver may also be separated in the form of sulphuret from old hypo
baths, by adding oil of vitriol in quantity sufficient to decompose the
hyposulphite of soda; and burning off the free sulphur from the brown
deposit.

_Conversion of Sulphuret of Silver into Metallic Silver._--The black
sulphuret of silver may be reduced to the state of metal by roasting and
subsequent fusion with carbonate of soda; but it is more convenient, in
operating on a small scale, to proceed in the following manner:--first
convert the sulphuret into nitrate of silver, by boiling with nitric acid
diluted with two parts of water; when all evolution of red fumes has
ceased, the liquid may be diluted, allowed to cool, and filtered from
the insoluble portion, which consists principally of sulphur, but also
contains a mixture of chloride and sulphuret of silver, unless the nitric
acid employed was free from chlorine; this precipitate may be heated in
order to volatilize the sulphur, and then digested with hyposulphite of
soda, or added to the hypo bath.

The solution of nitrate of silver obtained by dissolving sulphuret of
silver is always strongly acid with nitric acid, and also contains
_sulphate_ of silver. It may be crystallized by evaporation; but unless
the quantity of material operated on is large, it will be better to
precipitate the silver in the form of chloride, by adding common salt, as
already recommended.

       *       *       *       *       *

On the Use of Test Papers.

[Sidenote: ON THE USE OF TEST PAPERS.]


The nature of the coloring matter which is employed in the preparation of
litmus-paper has already been described at page 98.

In testing for the alkalies and basic oxides generally, the blue
litmus-paper which has been reddened by an acid may be used, or, in place
of it, the turmeric paper. Turmeric is a yellow vegetable substance which
possesses the property of becoming brown when treated with an alkali;
it is however decidedly less sensitive than the reddened litmus, and is
scarcely affected by the weaker bases, such as oxide of silver.

In using test papers observe the following precautions:--they should be
kept in a dark place, and protected from the action of the air, or they
soon become purple from carbonic acid, always present in the atmosphere in
small quantity. By immersion in water containing about one drop of liquor
potassæ in four ounces, the blue color is restored.

Test-papers prepared with porous paper show the red color better than
those upon glazed or strongly sized paper. If the quantity of acid present
however is small, it is not sufficient in any case simply to dip the paper
in the liquid; a small strip should be thrown in, and allowed to remain
for ten minutes or a quarter of an hour.

If the paper, on immersion, assumes a _wine-red_ or purple tint, in place
of a decided red, it is probably caused by carbonic aid gas: in that case
the blue color returns when the paper is washed and held to the fire.

Blue litmus-papers may be changed to the red papers used for alkalies by
soaking in water acidified with sulphuric acid, one drop to half a pint.

       *       *       *       *       *


The Salting and Albumenizing Paper.

[Sidenote: SALTING PAPER, ETC.]


Take of

  Chloride of ammonium, or pure chloride of sodium  200 grains.
  Water                                              10 fluid oz.
  Albumen                                            10 fluid oz.

If distilled water cannot be procured, rain water or even common spring
water[L] will answer the purpose. To obtain the albumen, use new-laid
eggs, and be careful that in opening the shell the yelk is not broken;
each egg will yield about one fluid ounce of albumen.

[Footnote L: If the water contained much sulphate of lime, it is likely
that the sensitiveness of the paper would be impaired (?).]

When the ingredients are mixed, take a bundle of quills or a fork, and
beat the whole into a perfect froth. As the froth forms, it is to be
skimmed off and placed in a flat dish to subside. The success of the
operation depends entirely upon the manner in which this part of the
process is conducted; if the albumen is not thoroughly beaten, flakes of
animal membrane will be left in the liquid, and will cause streaks upon
the paper. When the froth has partially subsided, transfer it to a tall
and narrow jar, and allow to stand for several hours, that the membranous
shreds may settle to the bottom. Pour off the upper clear portion, which
is fit for use. Albumenous liquids are too glutinous to run well through a
paper filter, and are better cleared by subsidence.

A more simple plan than the above, and one equally efficacious, is to
fill a bottle to about three parts with the salted mixture of albumen and
water, and to shake it well for ten minutes or a quarter of an hour, until
it loses its glutinosity and can be poured out smoothly from the neck of
the bottle. It is then to be transferred to an open jar, and allowed to
settle as before.

The solution, prepared by the above directions, will contain exactly ten
grains of salt to the ounce, dissolved in an equal bulk of albumen and
water. Some operators employ the albumen alone without an addition of
water, but the paper in that case has a very highly varnished appearance,
which is thought by most to be objectionable.

The principal difficulty in albumenizing paper is to avoid the occurrence
of streaky lines, which, when the paper is rendered sensitive, bronze
strongly under the influence of the light. The writer believes these to
be caused by a commencing decomposition of the animal matter composing
the cells in which the albumen is retained and the best remedy appears to
be to use the eggs quite fresh; the same object may sometimes (but not
invariably) be attained by allowing the albumen to stand for several weeks
until it has become sour; after which it will be sufficiently limpid to
run through a filter.

In salting and albumenizing photographic paper by the formula above given,
it was found that each quarter sheet, measuring eleven by nine inches,
removed one fluid drachm and a half from the bath; equivalent to about
one grain and three quarters of salt (including droppings). In salting
plain paper, each quarter sheet took up only one drachm; so that the
glutinous nature of the albumen causes a third part more of the salt to be
retained by the paper.

_Selection of the Paper._--The English papers are not good for
albumenizing; they are too dense to take the albumen properly, and curl
up when laid upon the liquid; the process of toning the prints is also
slow and tedious. The thin negative paper of Canson, the Papier Rieve, and
Papier Saxe, have succeeded with the writer better than Canson's positive
paper, which is usually recommended; they have a finer texture and give
more smoothness of grain.

To apply the albumen; pour a portion of the solution into a flat dish to
the depth of half an inch. Then, having previously cut the paper to the
proper size, take a sheet by the two corners, bend it into a curved form,
convexity downwards, and lay it upon the albumen, the centre part first
touching the liquid and the corners being lowered gradually. In this way
all bubbles of air will be pushed forwards and excluded. One side only of
the paper is wetted: the other remains dry. Allow the sheet to rest upon
the solution for one minute and a half, and then raise it off, and up by
two corners. If any circular spots, free from albumen, are seen, caused by
bubbles of air, replace the sheet for the same length of time as at first.

The paper must not allowed to remain upon the salting bath much longer
than the time specified, because the solution of albumen being _alkaline_
(as is shown by the strong smell of ammonia evolved on the addition of the
chloride of ammonium), tends to remove the size from the paper and sink in
too deeply; thus losing its surface gloss.

Albumenized paper will keep a long time in a dry place. Some have
recommended to press it with a heated iron, in order to coagulate the
layer of albumen upon the surface; but this precaution is unnecessary,
since the coagulation is perfectly affected by the nitrate of silver used
in the sensitizing; and it is doubtful whether a layer of dry albumen
would admit of coagulation by the simple application of a heated iron.

_To render the paper sensitive._--This operation must be conducted by the
light of a candle, or by yellow light. Take of

  Nitrate of Silver                                  60 grains.
  Distilled Water                                     1 ounce.

Prepare a sufficient quantity of this solution, and lay the sheet upon it
in the same manner as before. Three minutes' contact will be sufficient
with the thin negative paper, but if the Canson positive paper is used,
lour or five minutes must be allowed for the decomposition. The papers are
raised from this solution by a pair of bone forceps or common tweezers
tipped with sealing-wax; or a pin may be used to lift up the corner, which
is then taken by the finger and thumb and allowed to drain a little before
again putting in the pin, otherwise a white mark will be produced upon the
paper, from decomposition of the nitrate of silver. When the sheet is hung
up, a small strip of blotting-paper suspended from the lower edge of the
paper will serve to drain off the last drop of liquid.

The solution of nitrate of silver becomes after a time discolored by the
albumen, but may be used for sensitizing until it is nearly black. The
color can be removed by animal charcoal,[M] but a better plan is to use
the "kaolin" or pure white china clay. The writer has also tried the
common "pipe-clay," which answered perfectly, but appeared to injure the
sensitiveness of paper subsequently floated upon the bath (?).

[Footnote M: Common animal charcoal contains carbonate and phosphate
of lime the former of which renders the nitrate of silver _alkaline_;
purified animal charcoal is usually acid from hydrochloric acid.]

Sensitive albumenized paper, prepared as above, will usually keep for
several days, if protected from the light, but afterwards turns yellow
from partial decomposition.



=Comparison of British and French Weights and Measures.=

[Sidenote: WEIGHTS AND MEASURES.]

                      WEIGHTS.

  Grain,  Apothecaries'   =    0·0648 grammes, French.
  Ounce       "           =    31·102         "
    "     Avoirdupois     =    28·346         "
  Drachm, Apothecaries'   =     3·888         "

                        ----

  Gramme                  =    15·4310 grains, Apoth.
  Decigramme              =     1·5434   "       "
  Centigramme             =     0·1543   "       "

                        ----

                 MEASURES OF CAPACITY.

                  _Cubic Inches._   _Fluid Ounces._
  Litre       =    61·028          =      35·79
  Decilitre   =     6·02           =       3·57
  Centilitre  =     0·610          =       0·35
  Millilitre  =     0·061          =       0·03

                        ----

                         _Lb._      _Oz._
  Killogramme      =       2              3-1/4 Avoirdupois.

                        ----

                   MEASURES OF LENGTH.

  Metre       =  39·37 inches.
  Decimetre   =   3·93   "
  Centimetre  =   0·39   "
  Millimetre  =   0·03   "

                        ----

  Cubic inch of water at 32°     =         252·45 grains.
    "     "     mercury   "      =        3425·35   "
  Fluid oz. of water             =         437·50   "
    "    "           measures    =           1·73 cub. in.
  1 f. drachm                    =          54·68 grains.
  1 pint (New York)              =          27·68 cub. in.
  1 oz. bromine                  =           2-1/2 f. drachms.
  1 grain, Troy or Apoth.        =          1·097 gr. Avoir.
  1 lb. Avoir.                   =          7000 Troy grs.
  1   "                          =          7680 of its own grs.

  The drachm Avoirdupois is never used except in weighing silk.
  Pendulum vibrating seconds at New York    =  39·102 inches.

In weighing solids, few weights are really necessary if they are properly
assorted; nothing less than half a grain is likely to be useful, and
the series following will weigh any quantity from the half grain to two
thousand one hundred and ten and a half grains, by differences of only a
single grain.

The numbers are in grains, but the same principle may be carried out with
any other denomination, whether ounces, pounds, or tons.

  1/2, 1, 2, 3, 4, 10, 20, 30, 40, 100, 200, 300, 400, 1000, &c.

The artist should be provided with not less than three glass measures--one
of a pint, graduated to ounces--one of two ounces, graduated to
drachms--and one of two drachms, graduated to minims.

       *       *       *       *       *

=Lewis's Patent Glass Baths= for Nitrate of Silver Solutions.--Since the
foregoing pages have been in print this new article of Baths has been
introduced, and will probably supersede all others now in market. They
are encased in a box made expressly to hold them, and form a valuable
and important improvement in the apparatus used in the various Glass
processes.



INDEX.


    Aberration, chromatic, 23;
      spherical, 22.
    Acetic acid, 66.
    Albumen, 63;
      preparation of positive paper with, 206.
    Alcohol, 70;
      used in sensitizing paper, 201.
    Ammonia, 71.
    Ammonio-nitrate of silver, preparation and use of, 152.
    Animal charcoal, 74.

    Barium, chloride of, 77.
    Baths, glass, 211;
      gutta-percha, 34.
    Bichloride of mercury for whitening positives, 159.
    Bromide and iodide of potassium and silver, 60.
    Bromide of potassium, 73.
    Bromine, properties of, 72.
    Bromo-iodized collodion for positives, (ambrotypes), 58, 59;
      for negatives, 60.

    Camera boxes, 28.
    Camera, construction of, 28.
    Camera stands, 31.
    Carbonate of soda, 73.
    Chemical and visual focus, 21.
    China clay, 75.
    Chloride of ammonium, 77.
    Chloride of barium, 77.
    Chloride of gold, preparation of, 83;
      for toning, 155
    Chloride of sodium, 78.
    Chlorine, 75.
    Chromatic aberration, 22.
    Citric acid, 78.
    Cleaning glass plates, 129.
    Coating large glasses with collodion, 160.
    Collodion, manufacture of, 53;
      iodized for positives, 58, 59;
      for negatives, 60;
      mode of coating glasses with, 131;
      vials, 38.
    Collodio-Albumen process, Dr. Taupenot, 190.
    Color-boxes, 38.
    Cutting's patents and correspondence, 173.
    Cyanide of potassium, 79;
      use of, 63.

    Decomposition of light, 16.
    Developing solution for positives, 62;
      for negatives, 144, 145.
    Dippers, glass and gutta-percha, 34.
    Double iodide of potassium and silver, 61.

    Ether, preparation of, 79.

    Fixing positives on glass, 134;
      negatives on glass, 146;
      positives on paper, 155.
    Fluoride of potassium, 81.
    Fogging of collodion positives, 137.
    Formic acid, 81.
    Fulminating gold, 84.

    Gelatine, properties of, 82;
      for mounting photographs, 157.
    Glass, cementing, 158.
    Glass plates, cleaning of, 129;
      coating with collodion, 131;
      coating with albumen, 193.
    Glass rods, bending of, 158.
    Glycerine, its properties, 82.
    Gold, chloride of, preparation of, 85;
      for toning, 155.
    Grape sugar, 86.

    Hadow, Mr., Researches and Formula for making soluble cotton, 46;
      on iodizing collodion, 54.
    Head rests, 33.
    Helio, collodion process for positives and negatives, 164.
    Honey, 86.
    Humphrey's collodion gilding, 63.
    Hydrochloric acid, 87.
    Hydriodic acid, 87.
    Hydrosulphuric acid, 88.
    Hypo bath, 203.
    Hyposulphite of gold, 85.
    Hyposulphite of silver, 17.
    Hyposulphite of soda, preparation and properties of, 89.

    Instantaneous positives, 159.
    Iodide of ammonium, preparation of, 91;
      for iodizing collodion, 58, 59.
    Iodide of cadmium, 92.
    Iodide of iron, preparation of, 93;
      its uses and acceleration, 159.
    Iodide of potassium and silver, preparation of, 61;
      use in sensitizing collodion, 58, 60.
    Iodide of potassium, properties and preparation of, 94.
    Iodide of silver, preparation and properties of, 112;
      its use in the nitrate bath, 65, 147.
    Iodine, preparation and properties of, 90.
    Iodized collodion, 58, 59, 60, 131.
    Iron, perchloride of, 98.
      "   protonitrate of, 97.

    Jenny Lind stands, 32.

    Kaolin, properties of, 75.

    Lenses, double-convex, concavo-convex, double-concave, 19.
    Lenses, forms of, 19, 20;
      combination of, for portraits, 27;
      chromatic aberration of, 23;
      spherical aberration of, 22.
    Leveling stands, 35.
    Light, decomposition of, 16.
    Litmus, 98.

    Manipulations of the positive collodion process, 129;
      negative process, 143.
    Measures and Weights, 210.
    Milk, 99.
    Mounting positives on paper, 157.

    Negatives for printing positives, 151, 169.
    Nitrate of potash, 102.
    Nitrate of silver, 116.
    Nitrate of silver bath, mode of preparing for positives, 64;
      for negatives, 147;
      for negatives and positives in Helio's process, 164.

    Nitrate of silver used in developing negatives, 145.
    Nitric acid, preparation and properties of, 100;
      use in nitrate bath, 65, 147;
      use in making soluble cotton, 46.
    Nitro-sulphuric acid used in preparing soluble cotton, 42, 51.

    Oxide of silver, preparation of, 109.
    Oxygen, 109.
    Oxymel, preparation of, 105.

    Paper, sensitive, for printing, 152;
      alcohol used in, 201.
    Patent for the use of camphor in combination with iodized
      collodion, 176;
      for sealing photographic pictures, 177;
      for the use of alcohol as a desiccating agent, 178;
      for the use of bromide of potassium in collodion, 178;
      for the use of japanned surfaces for taking positives, 179;
      for photographic pictures in oil, 181;
      for making transparent borders, 183;
      coloring positives, 185, 187;
      for albumenized collodion, 186.
    Plate-Holders, Lewis's patent, solid glass corners for, 137.
    Plato vices, 64.
    Portrait lenses, combination of, 27.
    Positives, (ambrotypes,) process for producing, 129;
      by the Helio process, 164;
      printing on albumenized paper, 192, 206;
      ammonio-nitrate of silver used in, 152;
      use of chloride of gold in toning, 155;
      fixing, 155;
      fixing and brightening, (ambrotypes), Humphrey's collodion gilding
        used in, 63;
      printing frames for, 36; collodion for, 58, 59;
      mica used for, 136.
    Positives, enlarging from negatives, 199.
    Potash, 105;
      carbonate of, 106.
    Practice of the positive collodion process, 129;
      negative process. 143;
      Helio's positive and negative process, 164;
      printing on paper, 151.
    Prism, 14;
      refraction of light by, 14.
    Protosulphite of iron used in developing positives. 62;
      negatives, 144.
    Pyrogallic acid, preparation of, 107.

    Sensitizing paper, use of alcohol in, 201.
    Silver, properties of, 107;
      removal of stains from the nitrate of, 161;
      recovery of from waste solutions, 203.
    Solar spectrum, 14.
    Soluble cotton, 42;
      Hadow on, 46.
    Spherical aberration, 22.
    Spots upon positives, 139.
    Stains and lines upon positives, 139.

    Taupenot, M., his Collodio-albumen process, 190.
    Test-paper, use of, 205.
    Toning bath for positives on paper, 155.

    Weights and Measures, 210.

       *       *       *       *       *


CORRECTIONS.

[Transcriber Note: Corrections have been applied to text.]


On Page 61 and 16th line from the top, for "Iodide of Silver," read
_Iodide of Potassium_.

On Page 167 and 2nd line, for "32 ounces," read 64 _ounces_.



       *       *       *       *       *


Transcriber Note

Minor typos may have been corrected. Images were moved so as to prevent
splitting paragraphs. All images were derived from materials made
available on The Internet Archive and are placed in the Public Domain.





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