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.