GB676746A - Improvements in the preparation of photographic emulsions - Google Patents

Abstract

676,746. Photographic emulsions. KODAK, Ltd. (Eastman Kodak Co., Jones, J. E., and Ballard, A. E.). May 25, 1950 [Feb. 25, 1949], No. 5263/49. Addition to 676,745. Class 98 (ii). In the preparation of a photographic silver halide emulsion according to the parent Specification, ammoniated silver oxide stabilized against violent decomposition is prepared by dissolving silver oxide in an aqueous ammoniacal solution in the presence of an ammonium salt of an oxygen-containing acid, e.g. ammonium nitrate, carbonate, sulphate, citrate, acetate, or oxalate. The addition also reduces the tendency of the solution to deposit silver, and, in the case of ammonium carbonate, reduces the quantity of ammonia required. In an example, ammonium carbonate solution is added to washed silver oxide, and ammonia is then added to bring the silver oxide into solution. Silver halide is precipitated by adding this solution to an aqueous solution of gelatin, ammonium bromide, and a small amount of potassium or ammonium iodide, and excess ammonia and substantially all of the ammonium carbonate are removed by passing the mixture through a vacuum apparatus as described in the parent Specification. The preparation of the emulsion is completed in the usual manner. The precipitation of the silver halide may be effected by reacting an aqueous ammonia solution of silver oxide in the presence of gelatin and the ammonium salt with one or more alkali metal or alkaline earth metal halides (e.g. sodium or calcium bromide), with hydrobromic or hydrochloric acid, with ammonium bromide, chloride, or iodide, with pyridinium hydrobromide, or with a halide of formula RR 1 R 1 R 1 NX, wherein X is a halogen atom and R-R 3 are each a hydrogen atom or an alkyl group of 1 to 4 carbon atoms, the total number of carbon atoms in the R groups being from 0 to 4.