US1673522A - Process of manufacturing photographic silver halide emulsions and products obtained thereby - Google Patents

Description

Patented June 12, 1928 UNITED STATES PATENT oFFic s.

OTTO MATTHIES, OF DESSAU, PETER WULFF, F STARNBERG, AND WALTER DIETEELE AND BRUNO WENDT, OF DESSAU, GERMANY, ASSIGNOES TO I. G. FARBENINDUSTRIE AKTIEN'GESELLSCHAFT, OF FRANKFORT, GERMANY.

PROCESS OF IMANUFACTURING PHOTOGRAPHIC SILVER HALIDE EMULSION'S AND PRODUCTS OBTAINED THEREBY.

No Drawing. Application filed 311137 19, 1926, Serial No. 121,781, and in Germany July 25, 1925.

It is known that sulphydric acid or sul phides produce more or less fog in hotographic silver halide emulsions. Alt ough attempts have been made to add only very minute, exactlydefined, quantities of these chemical compositions, they generally are found to produce fog, although a certain increase in the sensitivity of the emulsion may be perceived at the same time.

The sensitivity of photographic silver halide emulsions ma be raised without fogging, according to t e present invention, by adding to the emulsion, during emulsion making, small quantities of salts soluble in water, the anions of which contain at least three atoms of sulphur. The addition may be made to the constituents of the emulsion, or at any step of emulsion making, or to the finished emulsion. 2a The compounds adapted to be added for this purpose, e. g. sodium trithionate, sodium tetrathionate, the sodium salt of the trithiodi-glycolic acid (COOH.OH,.S.S.S.CH .COOH) produce the desired effect in emulsions having an alkaline reaction, as well as in neutral and weakly acid emulsions. With silverions they form silver-compositions which so are diflicultly soluble in water and decom-' pose spontaneously producing a silver-metalloid-composition.

The decomposable silver-sulphur-compounds having been formed in the silver halide crystals formerly free from sulphur,

or on their surfaces, the. decomposition producing silver-metalloid takes place in the emulsion. The invention depends on the knowledge that the sensitivity of photo- 40 graphic emulsions is raised in a particularly good manner when traces of silver-metalloid, especially of silver sulphide,constituting reducing agents,--are produced by the de- A com osition of the above-mentioned decomposa le compounds inside of the silver halide crystals or on their surfaces. The use of soluble sulphides or of colloidal silver sulhide solutions never results inanalogous increases in the sensitivity of the halide emulsions.

Selenium and tellurium are equivalent tobe raised.

Example 1.

To a photographic silver halide emulsion prepare from 1 kg. of gelatine and 4.00 g. of silver nitrate, there is added 50-100 mg. of sodium trithionate. By this addition the sensitivity increases from 12 to 17 Scheiner.

y Example 2. The same effect is reached by substituting for; the sodium trithionate in Example 1,

30-40 mg. of the sodium salt of the trithiodi-glycolic acid.

Example 3.

' To the emulsion manufactured according to Example 1, there is added, instead of sodium trithionate, 5 com. of a n TO solution of potassium selenotrithionate which is obtained by dissolving selenium in-potassium sul hite.

aving now particularly described andascertained the nature of our invention and in what manner it is to be performed, we declare that What we claim is:

1. Process of making a photographic silver halide emulsion which comprises ,incorporating in said emulsion a water-soluble salt the anions of which contain at least three atoms of an element of the sulphur g in; 2. rocess of manufacturing photographic silver halide emulsions which comprises addin to the emulsion Water-soluble saltsthe anions of which contain at least three atoms of an element of the sulphur group.

elatine, particles of silver halide suspended t erein, and a small amount of a water-solu- 15 Me compound the anions of which contain at least three atoms of sulphur.

7. Photographic layers comprising the silver halide emulsion defined in claim 6.

In testimony whereof we aflix our signa- 90 ture s.

OTTO MATTHIES.

WALTER DIETERLE. PETER WULFF.

BRUNO WENDT.