IMPROVEMENTS IN COMPOSITIONS TO BE USED IN THE PREPARATION OF SENSITIVE PHOTOGRAPHIC PLATES
Year: 1879

page_text: LETTERS PATENT to Joseph Horatio Ritchie, of 57, Fenchurch Street, in the
City of London, for the Invention of "IMPROVEMENTS IN COMPOSITIONS TO BE
USED IN THE PREPARATION OF SENSITIVE PHOTOGRAPHIC PLATES."
Sealed the 18th November 1879, and dated the 26th May 1879.
PROVISIONAL SPECIFICATION left by the said Joseph Horatio Ritchie at
the Office of the Commissioners of Patents on the 26th May 1879.
JOSEPH HORATIO RITCHIE, of 57, Fenchurch Street, in the City of London.
"IMPROVEMENTS IN COMPOSITIONS TO BE USED IN THE PREPARATION OF SENSITIVE
PHOTOGRAPHIC PLATES."
This Invention has for its object improvements in compositions to be used in
the preparation of sensitive photographic plates.
At the present time one description of sensitive photographic plates is now
prepared with gelatine in which bromide of silver is suspended, a mixture which
is known as gelatino-bromide of silver.
Gelatino-bromide of silver has hitherto been prepared by various methods, the
bromide of silver having generally been formed in the gelatine itself. My Inven-
tion consists in forming such bromide in a mucilage of gum, and I prefer to use for
this purpose gum arabic purified by being deposited from a solution by excess of
alcohol called Arabin, this after having been dried is again dissolved in water, and
the bromide of silver is formed in it by the mixture therein of a bromide salt and
nitrate of silver, as has hitherto been done in gelatine solution. This mixture is
dialysed until the free salts have been eliminated and alcohol is added to it; it is
then ready for use at any time, and when required the gelatine is added and
dissolved by warmth, and the plates are coated.
In some cases I pass a current of electricity through the sensitising solution or
mixture, by which I believe it to be in some respects improved.
Amongst the advantages of this Invention are,-
1. The facility of using any quantity of bromide of silver in proportion to
gelatine, and varying it to suit various descriptions of subjects.
2. The facility with which the free salts can be with certainty eliminated.
3. The convenience of having the bromide of silver mucilage ready to make any
quantity of any sized plates required.
4. The uniform quality of the plates, their great sensitivenes, and the facility of
using them.
5. Immunity from the defect known as frilling or wrinkling of the film, so
common in gelatino-bromide of silver plates made by the ordinary methods.

page_text: "
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Joseph Horatio Ritchie in the Great Seal Patent Office on the
26th November 1879.
JOSEPH HORATIO RITCHIE, of 57, Fenchurch Street, in the City of London.
"IMPROVEMENTS IN COMPOSITIONS TO BE USED IN THE PREPARATION OF SENSITIVE
PHOTOGRAPHIC PLATES."
This Invention has for its object improvements in compositions to be used in
the preparation of sensitive photographic plates.
At the present time one description of sensitive photographic plates is now
prepared with gelatine in which bromide of silver is suspended, a mixture which
is known as gelatino-bromide of silver.
Gelatino-bromide of silver has hitherto been prepared by various methods, the
bromide of silver having generally been formed in the gelatine itself. My Inven-
tion consists in forming such bromide in a mucilage of gum, and I prefer to use
for this purpose gum arabic purified by being deposited from a solution by excess
of alcohol called Arabin, this after having been dried is again dissolved in water,
and the bromide of silver is formed in it by the mixture therein of a bromide salt
and nitrate of silver, as has hitherto been done in gelatine solution. This mixture
is dialysed until the free salts have been eliminated and alcohol is added to it; it
is then ready for use at any time, and when required the gelatine is added and
dissolved by warmth, and the plates are coated.
Amongst the advantages of this Invention are,—
1. The facility of using any quantity of bromide of silver in proportion to
gelatine, and varying it to suit various descriptions of subjects.
2. The facility with which the free salts can be with certainty eliminated.
3. The convenience of having the bromide of silver mucilage ready to make any
quantity of any sized plates required.
4. The uniform quality of the plates, their great sensitiveness, and the facility of
using them.
5. Immunity from the defect known as frilling or wrinkling of the film, so
common in gelatino-bromide of silver plates made by the ordinary methods.
Having described the general character of my Invention, I now proceed to
describe fully the method of making the bromide of silver emulsion.
The emulsion being preferably made with Arabin, rather than gum arabic, being
more reliable, I first describe a convenient method for preparing that substance.
I lavigate to a fine powder that it may more rapidly dissolve, say, 10 ounces of
the purest gum arabic, and pour on it 12 ounces of distilled water, and well stir it
until thoroughly dissolved; I then add 15 ounces of pure absolute alcohol, and stir
it well when the Arabin goes to the bottom, and allows the water with soluble
impurities of the gum and the alcohol to be poured off; I further add 7 ounces
of the same alcohol, stir it, and pour it off, and repeat the same again; I then
place the Arabin in a clean cloth, and wring out the most of the remaining alcohol,
and dry it up finally by spreading it out on a tray in a warm place; it is, then
bottled and kept ready for use.
To make the emulsion, the formula I prefer, say, for a quantity of 5 ounces, is as
follows:-
55 grains of the above described Arabin or gum arabic are thoroughly dissolved
in 1 ounce of distilled water, filtered through bibulous paper or a piece of cotton
wool in the neck of a funnel, and poured into a jar or convenient vessel for mixing
the emulsion.
300 grains of recrystallised nitrate of silver are dissolved in 5 drachms of distilled
water filtered through bibulous paper, measured and carefully divided into four
equal portions, which are poured into four phials or convenient vessels.
250 grains of bromide of potassium are dissolved in 2 ounces of distilled water,

page_text: filtered through bibulous paper, measured and accurately divided into four equal
portions, which are put into convenient vessels in the same manner as the nitrate
of silver solution.
Thus far the process may be done by day light or gas light, but before the
mixture of these ingredients (which renders the substance sensitive) the light must
be screened by passing through a non actinic medium, such as chrysoidine dyed
paper or orange ruby glass.
The first portion of the solution of the bromide salt is now poured into the
mixing jar and well mixed with the solution of Arabin or gum arabic, and the first
portion of the nitrate of silver solution is added, then the second portion of the
bromide solution is poured in and mixed, and is followed by the second portion of
the nitrate of silver solution, and the third portions of the salts are similarly added,
but not the fourth portions, as previous to that the emulsion must be partly cleared
of the large quantity of soluble salts which it now contains by placing it in a
dialyser, arranged as afterwards described, for about twelve hours, when it is
returned to the jar or mixing vessel, and the fourth portion of the bromide solution
followed by the nitrate of silver solution are added and well mixed in the same
way as described for the first and other portions.
The emulsion is then replaced in the dialyser and allowed to remain there in
contact with water (which has to be frequently changed) until the soluble salts
have passed through the diaphragm, which can be ascertained by placing a few
drops at intervals of about twelve hours on a piece of glass or other similar
substance, and allowing them to dry when the salts will shew their presence by
forming crystals on the surface, and when such spots dry with a bright surface it
shews that the main portion of the excess of bromide salt and salts formed by the
decomposition have passed through, and a further time in the dialyser equal to
about two thirds of the time taken for the crystals to disappear will practically
clear the solution from soluble salts, when it will only be necessary to add 7
drachms of pure absolute alcohol, and any water required to make up the 5 ounce.
quantity to filter it through bibulous paper, or with greater facility through
cotton wool placed in the neck of a funnel, and finally to bottle and secure it from
any accession of light.
On dialysing it is important to adjust the height of the dialyser with reference
to the surrounding water, so that there may be as little as possible either of a flow.
into or out of the dialyser, it being supported at a proper height for this purpose.
This is an exact description of the preparation of one sort of the emulsion,
which I prefer as giving excellent results and being uniform in quality, but great
varieties may be made by slight modifications of the process, namely, a larger
addition of Arabin or gum arabic will allow the above mentioned quantities of the
bromide and silver salts to be added without any intermediate dialysing previous
to the last addition; this saves a little time, a smaller or larger quantity of the
bromide and silver salts may be used with the same or a larger portion of Arabin
or gum arabic, the salts may be added in a larger or smaller number of portions,
the former tending to form the bromide of silver in a molecular state supposed to
be finer than the former, it being more transparent to transmitted light. The salts
may be added in varying quantities, the bromide salt and its following portion of
nitrate of silver solution always having the same proportion to each other, so that
the bromide may be always in excess to the same extent, the bromide salt may be
added in a decreasingly concentrated solution, or the nitrate of silver solution may
be more diluted at first than at the last additions, so that the first deposit of
bromide of silver may not be quite so fine, or the last quite so coarse as it other-
wise is, for the solution of Arabin, &c., being at first free from soluble salts, and at
the end strongly charged with them, the deposit becomes more and more coarse
and diluting the bromide salt or strengthening the nitrate of silver solution more
and more towards the end tends to counteract this. The bromide salt may be
added to the Arabin, and at the several stages in a dry state, the water which
>

page_text: would otherwise have been mixed with it being added to the Arabin or gum arabic,
either in equal or varying portions during the process.
In whatever way the bromide salt is added it is important to observe that it
must be at all times a little more than necessary to convert the nitrate of silver
which is to be added in the several instalments, and with reference to the kind of
bromide salt to be used; I prefer bromide of potassium, because the soluble salt
which it forms by decomposition crystallizes distinctly on the surface of the
dialysing testing portions above mentioned; other bromide salts may however be
used in quantity, similarly proportioned to the bromide contained in them.
By following the first above described exact formula it will be found that a very
good emulsion may be prepared, and by modifying it according to the general
principles indicated afterwards great varieties in the molecular condition of the
bromide of silver may be produced.
.
The emulsion having been made as above described, and stored for use, is to be
used as follows:-
For every ounce of the emulsion used, I take 10 grains of the strongest and
purest gelatine, and place it in a phial or other convenient vessel, and pour on it
clean water (hard or soft) until it is covered, when it is allowed to soak until quite
soft, the excess of water is then poured off and the ounce of emulsion added to the
soaked gelatine, the phial or other vessel with the emulsion and gelatine in it is
then plunged into hot water until quite warm and dissolved, when the bottle is
well shaken to mix the contents, and when this is done it is passed through a
piece of cambric in a funnel into a small beaker or other vessel, and poured on
glass plates in the manner usual in the preparation of gelatine plates, which plates
are then dried in a level position exposed when required, and developed with the
various developers at present in use for developing gelatine plates, and are fixed in
the usual manner.
Having now fully described the method of making and using this substance, I
claim as my Invention,-
First. The use of Arabin or gum arabic as a vehicle for keeping in suspension
bromide of silver in a suitable condition, and the addition of bromide of silver thus
held in suspension to gelatine for the preparation of photographic sensitive plates.
Second. The above described methods by which I produce and suspend in a
solution of Arabin or gum arabic bromide of silver in a pure, stable, sensitive
condition, suitable and ready for the production of sensitive photographic plates.
In witness whereof, I, the said Joseph Horatio Ritchie, have hereunto set
my hand and seal, this Twenty-fourth day of November, in the year of
our Lord One thousand eight hundred and seventy nine.