An Improved Process for Making Silver Halogen Emulsions Sensitive to Light.
Year: 1898

page_text: An Improved Process for Making Silver Halogen Emulsions
Sensitive to Light.
I, MAX PETZOLD, of 23, Langestrasse, Chemnitz, in the Empire of Germany,
Chemist, do hereby decláre the nature of this invention to be as follows;-
This invention has for its object a process intended to be employed for making
silver halogen emulsions sensitive to light, so that thereby dry plates and papers
sensitive to light may be made which only require alkaline solutions for their
development. The process is explained in the following way:-
If reducing substances be added to a bromide or chloride of silver emulsion
ready for running or coating, the emulsion is decomposed on drying, in conse-
quence of the energetic tendency to oxidation of the developing substance..
In order to avoid this, the simultaneous addition of sulphide of soda is pro-
posed but this is a failure owing to its also being exposed under certain circum-
stances to very energetic oxidation, that is to say, it is very easily decomposed
because sulphite of soda in and of itself has an alkaline reaction
whilst the reduction chemicals are only oxidised in this (alkaline) solution.
If this easy oxidation of suphite of soda could be avoided, the oxidation of the
developing substance in the emulsion could also be avoided. This is easily
attained if, in place of sulphite of soda, bisulphite he employed, which is only
slightly constant and decomposes into sulphite and sulphurous acid. The sul
phurous acid thereby released prevents in statu nascendi the oxidation of the
resultant sulphite and also of the developing substance, whilst on the other hand
the silver salt is guarded against reduction in the emulsion. These appearances.
are also assisted by the acid reaction.
The same result is attained with the use of acids in the presence of or without
sulphite of soda instead of bisulphite. The sulphite of soda is then converted
into a soda salt of the actual acid employed whilst sulphurous acid is released.
The process which forms the object of the present invention allows of sensitive
dry plates and papers being produced, the emulsions of which contain developing
substances and for the development of which only alkaline solutions are necessary.
The following is an example of one means of carrying out the invention.
300 grammes of developing substance, such for instance as hydroquinone,
pyrogallic acid, eikonogen paramidophenol, glycin, metol or other suitable reduc-
ing substances employed for photography are added to 10 litres of emulsion ready
for use, the said reducing substance being in turn treated up to 20% of its

page_text: weight with an acid sulphite or with sulphite of soda and organic acids which
are thoroughly well stirred poured out and allowed to dry.
Dated this 7th day of May 1898.
W. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.
An Improved Process for Making Silver Halogen Emulsions
Sensitive to Light.
I, MAX PETZOLD, of 23, Langestrasse, Chemnitz, in the Empire of Germany,
Chemist, do hereby declare the nature of this invention, and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement;-
This invention has for its object a process intended to be employed for making
silver halogen emulsions sensitive to light, so that thereby dry plates and papers
sensitive to light may be made which only require alkaline solutions for their
development. The process is explained in the following way:-
If reducing substances be added to a bromide or chloride of silver emulsion
ready for running or coating, the emulsion is decomposed on drying, in conse-
quence of the energetic tendency to oxidation of the developing substance.
In order to avoid this, the simultaneous addition of sulphite of soda is pro-
posed but this is a failure owing to its also being exposed under certain circum-
stances to very energetic oxidation, that is to say, it is very easily decomposed
an alkaline
because sulphite of soda in and of itself has
reaction
whilst the reduction chemicals are only oxidised in this (alkaline) solution.
If this easy oxidation of sulphite of soda could be avoided, the oxidation of the
developing substance in the emulsion could also be avoided. This is easily
attained if, in place of sulphite of soda, bisulphite be employed, which is only
slightly constant and decomposes into sulphite and sulphurous acid. The sul-
phurous acid thereby released prevents in statu nascendi the oxidation of the
resultant sulphite and also of the developing substance, whilst on the other hand
the silver salt is guarded against reduction in the emulsion. These appearances
are also assisted by the acid reaction.
The same result is attained with the use of acids in the presence of or without
sulphite of soda instead of bisulphite. The sulphite of soda is then converted
into a soda salt of the actual acid employed whilst sulphurous acid is released.
The process which forms the object of the present invention allows of sensitive
dry plates and papers being produced, the emulsions of which contain developing
substances and for the development of which only alkaline solutions are necessary.
The following is an example of one means of carrying out this invention.
300 grammes of developing substance, such for instance as hydroquinone,
pyrogallic acid, eikonogen paramidophenol, glycin, metol or other suitable reduc-
ing substances employed for photography are added to 10 litres of emulsion ready
for use,
the said reducing substance being in turn treated up to 20% of its
weight with an acid sulphite or with sulphite of soda and organic acids which
are thoroughly well stirred, poured out and allowed to dry.
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the same is to be performed, I declare that what
I claim is:-
A process for making sensitive silver halogen emulsions with reducing sub-

page_text: stances for producing sensitive dry plates and papers, characterised by their.
emulsions containing developing substances to which materials which directly
reduce the emulsions are added in the presence of acid sulphite, or sulphite with
organic acids, so that only dissolved alkali is employed for developing said
plates or papers, substantially as herein before set forth.
Dated this 8th day of February 1899.
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.