van Monckhoven, Désiré van.
A Popular Treatise on Photography. Translated By W.H.
Thornthwaite. London, 1863.
On the Preparation of Substances Required in the Manufacture of
A MIXTURE of alcohol, sulphuric ether, and
gun-cotton forms a liquid called plain collodion, to
which is added, to render it suitable for photographic purposes, an
iodide or bromide; it is then termed iodised or sensitised
Spirits of wine, or alcohol, is a liquid well known, and can
generally be procured sufficiently pure for photographic purposes.,
it boils at about 172° Fahr., and burns with a bluish flame
without leaving a residue. One hundred ounces by weight of alcohol
measure about 125 fluid ounces, and 100 fluid ounces weigh about 80
ounces. It should be perfectly clear, transparent, and absolutely
free from any floating impurities; should it be otherwise, it must
be carefully filtered. The operation of filtering, applicable to
other liquids as well as alcohol, is thus performed. A circular
sheet of filtering paper is first folded in two, as
represented by Figs. 7 and 8; then a new fold is made in the middle,
Fig. 9; the filter is then opened out, as shown at Fig. 10, and
placed in a funnel, b furnished with its support, Fig. 11.
The alcohol or other fluid to be filtered, is poured carefully into
the filtering paper, through which it will pass perfectly clear.
Should the first portion that runs through not be quite bright, it
must be returned to the filter. When a very rapid Fig. 12. Plaited
filtration is desired the filter paper may be folded into a number
of plaits, as shown at Fig. 12, which affords a larger surface of
paper for the liquid to pass through.
Figs. 7, 8, 9, 10. Method of folding Filtering
Fig. 11. Apparatus for Filtering Papers.
Fig. 12. Plaited Filter.
Figs. 13, 14, Hydrometer and Glass
The strength of alcohol is conveniently ascertained by a specific
gravity hydrometer. This instrument is formed of glass, Fig. 14. It
consists of a glass bulb with a glass stem attached at the top, and
a smaller bulb filled with mercury, to serve as a counterpoise at
the bottom. In the stem is placed a graduated scale of specific
gravities, and the whole is so arranged that when placed in pure
distilled water, the instrument floats, and the surface of the water
is coincident with 0 or 1000 on the scale. When placed in alcohol or
any fluid lighter than water, the hydrometer sinks according to its
strength or specific gravity. A test-glass or cylinder, Fig. 13, is
used to hold a sample of the alcohol or other liquid to be tested,
and care must be taken when the hydrometer is placed in it that it
floats perfectly free in the fluid, and that no air bubbles attach
them selves to its surface. The specific gravity is. then
immediately indicated by noting the degree cut by the surface of the
fluid. alcohol, suitable for photographic purposes, should not have
a greater specific gravity than .819. Its best strength is about
.803 to .810.
It is comparatively easy to procure alcohol of sufficient purity
for photographic use, to what it is to obtain pure sulphuric ether.
When manufactured on a large scale for ordinary pharmaceutical
purposes, there is generally so
little care taken, that the ether becomes contaminated with
sulphovinic acid aldehyde, or, worse than all, a peculiar principle
resembling ozone, which is capable of decomposing iodides and
liberating free iodine, sherries, highly detrimental to its
photographic action, The formation of this substance is touch
accelerated by the joint nation of air and light; the knowledge of
this circumstance is, therefore, of soma importance to
photographers, as it indicates a very necessary precaution to be
taken to keep ether, mod liquids containing it, particularly
collodion, it yell filled and closed bottles.
Sulphuric ether is a colourless liquid, and very volatile; whom
poured into water it boats about like oil, and a very smell quantity
is dissolved. It is much lighter than water, 10, ounce. by weight of
ether being equal in volume to 106 ounces by weight of water. Ether
is tested to, to its strength by the specific gravity hydrometer, in
the same manner as described for alcohol on the opposite page. It
should have a specific gravity of .750 to .720 to be of any use in
In consequence of the highly volatile nature of ether and
its vapour being very explosive when mixed with ,atmospheric air, it
is necessary, to prevent accidents, to avoid pouring ether from one
vessel to another in a close room, or in proximity to a fire, or
flame. As the vapour of ether is much heavier than the air, it
naturally tends to fall, and therefore it is n proper precaution to
take, when employing ether or fluids containing it--as collodion,
for example--by artificial light, to have the source of light
situated at some distant, above the vessel from which the ether or
collodion is poured.
Ether, if not sufficiently pure for photographic purposes. can
generally be made available by the following method of
Into a tall bottle, Fig. 15, is to be poured the ether to be
purified, together with one-fourth of its volume of water, and the
opening closed with a cork; the whole is them strongly agitated, and
left to settle for some few minutes. Two layers of liquid will be
perceived the under layer being water slightly etherised, and the
upper ether. The cork is now removed, and the shorter end of an
ordinary glass syphon, having a small bore, and previously filled
with water, is introduced through the neck of the bottle, and quite
to the bottom of the liquid. The smallness of the bore, and keeping
the finger over the longer end of the tube, will enable the above to
be done with facility, without the water from the syphon running
out. The finger being removed, the syphon begins to act, and the
etherised water from the bottom of the bottle is quickly drawn off.
When the under layer has nearly disappeared, the orifice of the tube
is again stopped with the finger, and the syphon removed.
Fig. 16., Fig. 15.
A fresh quantity of water is now poured into the bottle
containing the ether, which is again agitated and drawn off by the
syphon as before explained.
This operation is called "washing," and the ether after this
process is called "washed ether."
Fig. 17. Bottle with underlayer of liquid has
passed over, the Syphon.
If bent glass tubes can be conveniently made or obtained, the
following arrangement may be found more convenient than the ordinary
syphon, it is shown at Fig. 17: A, the bottle where the ether and
water is shaken together; it is furnished with a good cork pierced
with two holes, in one of which is fitted a narrow tube (a) about
3/8ths of an inch internal diameter, and in the other, a curved
syphon tube (b), of which the shorter end inside the bottle
reaches to the bottom. If the cork be properly fitted, it is only
necessary to blow slightly through the tube (a) to cause the
liquid to rise in the tube (b) and flow over. When nearly the
whole of the syphon is stopped with the finger, the cork removed,
and the fresh quantity of water added, and the operation gone
through a second time.
The ether having been well washed, now requires to be dried and
distilled; this is done by pouring the ether remaining in the
washing bottle into a distilling weasel containing some few pieces
Fig. 18. Apparatus for distilling Ether.
A convenient arrangement of apparatus for the distillation of
small quantities of ether, is shown at Fig. 18; where larger
quantities are operated on, the;lass retort should be replaced by a
vessel of zinc or tin plate. A is a small furnace for charcoal, B a
vessel of copper or iron of some convenient form, to hold a small
quantity of water, C a glass retort or other vessel, the opening of
which is attached, by means of a cork, to a small leaden tube abort
the thickness of the little finger, and 1½ yards long; a
portion of this tube is surrounded by another about 2 inches in
diameter, and ¾ths of a yard long; the top and bottom of this
tube is closed perfectly water-tight round the smaller tube, it has
also an overflow tube (a) at the top part, and a funnel and
tube (b) at the bottom, through which a stream of cold water
can be passed from any convenient vessel, as F, and
discharged into the receptacle H. The end of the small leaden
tube is bent so as to dip into a perfectly clean bottle (G);
in every other respect the figure will convey a correct idea of the
construction of the apparatus.
When about to be used, each separate part of the apparatus should
be perfectly cleaned and washed out with water, and arranged as
described and shown in the cut. The glass retort (C) or other
vessel, is filled for about one-fourth its volume, with small pieces
of quick lime, and the washed ether poured on to it until two thirds
of the bulk of the retort is filled; the end of the leaden tube is
then attached to the neck of the retort, and. the refrigerator E D
arranged in an inclined position, and firmly fixed by its support
(d) so that the bent end of the tube dips into the mouth of the
bottle G, which is to receive the distilled ether. The whole being
thus arranged, a small quantity of water is poured into the vessel
B, so that the lower portion of the retort C is immersed in it,
forming what is called a water bath some lighted charcoal is now
placed in the furnace fl. and the water in the vessel B becoming
heated, communicates its beat to the ether in the retort, which
begins to evaporate, and in a short time drops of ether appear at
the bottom of the leaden tube, and the distillation begins.**
The water in the vessel B gets more and more heated as the bulk
of ether in the retort diminishes, until no more drops are perceived
to fall from the end of the tube; the fire is now removed, the
apparatus separated, and the retort (C) or other vessel at once
cleaned out, for should this be delayed, it becomes very difficult
The heat of the fire must be kept as much as possible from the
bottle (G) containing the distilled ether, and a current of very
cold water passed through the refrigerator E D, otherwise the ether
vapour is not condensed. Sulphuric ether, rectified in the manner
described, although not absolutely and chemically pure, is
nevertheless well adapted for photographic purposes.
Gun-cotton, also termed "pyroxyline," is nothing more than
ordinary cotton combined with peroxide of nitrogen. It can be
prepared by plunging cotton wool for a few minutes into concentrated
nitric acid, then washed in water and dried; but in order to obtain
a good pyroxyline for photographic purposes, a particular process
must be followed, and a rigorous attention paid to each separate
detail. Gun-cotton in appearance much resembles ordinary cotton, but
it is heavier, and its fibres break more easily; it possesses also a
slightly yellow tint, which resembles that of raw cotton as imported
into Europe from the colonies. It is insoluble in water, alcohol,
pure ether, sulphuret of carbon, or chloroform, but it dissolves in
acetate of ethyle and methyle, methylic alcohol, acetone, and also
in alcoholised ether.
Pyroxyline burns with violence when brought in contact with any
flame; so much so as in many instances to answer the purpose of
The solution of gun-cotton in alcoholised ether is called
collodion, and is employed in surgery and photography; but for this
latter purpose it requires to be specially manufactured.
The following is the method of preparing gun-cotton for
photography, although we strongly recommend its being purchased
ready made, as photography being now so extensively employed,
gun-cotton is prepared on a large scale, and at a low price.
In a porcelain mortar is placed 2 ozs. of saltpetre in fine
powder, and over it is poured 3 ozs. by weight of sulphuric acid of
commerce. With the pestle, or a large glass tube, the materials are
well mixed, so as to obtain a homogeneous paste. In this is
immersed, in successive portions, ¼ oz. of carded cotton,
free from any mechanical impurities. The cotton is pressed down with
the pestle until thoroughly wetted and imbedded in the liquid paste.
The mortar is then covered with a plate, to prevent the nitrous
vapours which are given off from vitiating the air of the
laboratory. It is also advisable to perform this operation, if
possible, in the open air.
The cotton is left in this mixture for ten minutes; the mortar is
then placed in an inclined position, and water poured into it, at
the same time pressing the cotton with the pestle so as rapidly to
remove the excess of acid. After washing for a half minute in this
manner, it is taken up with the hands and thrown into a wooden tub
filled with water, and well kneaded; or else held under a watercock,
and constantly worked about, and from time to time pressed strongly
between the hands. This washing should be thoroughly done, until a
portion of the cotton, when put, in contact with blue litmus
paper.1 does not produce a
red stain. It is then strongly pressed, and left to dry in the air
or in the sun, having previously spread it oat thinly, so as to
present a large surface to the air. When the cotton is dry it is
preserved in glass bottles, well stopped. Gun-cotton, thus prepared,
very often gives traces of sulphate of potass; but as this substance
is absolutely insoluble ether and alcohol, it is of no
Large quantities of gun-cotton should not be bought or ,prepared
at one time, as it appears to be liable to decompose by keeping.
Gun-cotton, or pyroxyline, can be prepared according to the
formula given above from paper, linen, or hemp; but these
preparations have not been sufficiently studied for us to recommend
their employment in photography.
At the end of this volume3 Some
details are given relative to the manufacture of gun-cotton. on a
large scale by a mixture of nitric and sulphuric; acids. In
,general, the gun-cotton so prepared is less soluble than that which
has just been described; it, however, yields an excellent collodion,
especially adapted for coating large plates, from its being very
Gun-cotton was discovered by M. Schonbein, a German chemist ill
1846. The photographic process which employs collodion as its basis
was first described by Mr. Archer, in England, in 1861. M. Schonbein
prepared bun-cotton by steeping cotton in monohydrated nitric acid.
Afterwards M. Meynier discovered the advantage of using a mixture of
concentrated nitric and sulphuric., acids, and the method of
preparation with saltpetre and sulphuric acid is clue to M. Marc
Antoine Gaudin, calculator in the Bureau des Longitudes of
In connection with the method of preparing collodion, presently
to be described, will be indicated some other important points as
further guides to the selection or manufacture of a good
4. The Iodides and Bromides employed in
the Preparation of Photographic Collodion
A great number of iodides, bromides, and their compounds have
been at various times proposed for sensitising collodion, but the
formula most to be recommended is a mixture of iodide and
bromide of cadmium. In Note
4 will be found some remarks on the employment of the iodides
and bromides of potassium and ammonium.
Cadmium is now easily procured, almost, in a pure, state,
and at a comparatively cheap price. This metal is generally found in
commerce in small cylindrical ingots, about four inches in diameter,
and one-fourth in diameter. Its purity can be known by its making a
ringing crackling noise when bent, like tin. If it bends with
difficulty, and produces no sound when bent, it contains some other
metals, usually copper and zinc.
Iodine is a crystalline substance, having the aspect of
black-lead, or plumbago, volatile at a slight increase of
temperature, giving off purple vapours, highly corrosive, and
irritating to the eyes; it should always be preserved in glass
-stoppered bottles. It is obtained from the ashes of burnt
Bromine.--This substance is obtained froth sea-water,
after all the common salt has been removed by boiling. It is a very
dense, dark, red liquid; its vapour is highly injurious and
corrosive, and, froth its great volatility, is always kept under a
stratum of water or sulphuric acid, and in glass-stoppered bottles.
Both iodine and bromine are easily procured from any chemist.
Iodide of cadmium is thus prepared:-In a glass flash-, containing
a quart of water, at first put in 8 ozs. of iodine, and immediately
after 4 ozs. of cadmium in small pieces. The flask is placed on a
stove, moderately heated, in such a manner that the water in the
flask shall be kept only warm, not boiling. At the end of a few
hours, especially if shaken from time to time, the liquid, from red,
which it was at first, will become entirely colourless. Leave it to
cool, and then filter. The cadmium that remains may be used for
The solution of iodide of cadmium thus obtained, is evaporated in
a porcelain capsule. After a certain time crystals will appear in
the liquid. It is then placed on a very hot stove, where all the
water is driven off, and a dry mass obtained. The resulting
substance is detached from the capsule with a knife, then reduced to
a fine powder in a mortar, and finally preserved in a stoppered
The iodide of cadmium thus prepared is of a yellow tint, very
soluble in water and alcohol, but less soluble in ether.
Bromide of cadmium is made by pouring 6 ozs. of bromine into 1
quart of water, contained in a stoppered flask; 4 ozs. of cadmium,
in small pieces, are now added, and the flask closed. This mixture
is left for some days, and very carefully shaken from time to time;
the liquid gradually becomes discoloured, from the absorption of the
bromine; when this takes place it is filtered and evaporated to
dryness, as described for iodide of cadmium.
Bromide of cadmium is of a white colour, and less soluble in
water and alcohol than the iodide. These substances, when prepared
for sale on a large scale, are obtained beautifully crystallised,
which may be taken as an evidence of their purity.