GB472639A - Improvements in and relating to the preparation of photographic emulsions - Google Patents

Abstract

472,639. Photographic silver halide emulsions. CLAUS, B. March 25, 1936, No. 8939. Convention date, April 5, 1935. [Class 98 (ii)] Emulsions of medium grain and high sensitivity are prepared by forming a precipitate of silver halide, especially silver bromide, freeing this from the reaction products by decantation emulsifying it in a binder such as aqueous gelatin solution and allowing it to ripen therein and then adding to the emulsion so formed further silver halide which may be emulsified in a binding medium, and allowing the mixture to ripen further at a suitable temperature with if desired the addition of a ripening agent such as ammonia. In one example, solutions of potassium bromide containing some potassium iodide, and of silver nitrate are mixed and the precipitate washed. Part of this precipitate is then emulsified in gelatin with addition of ammonia and the mixture heated. The rest of the precipitate is then gradually added and sufficient gelatin to produce the desired content thereof is added. In another example, the precipitate formed as before is emulsified in gelatin and divided into two parts, to one of which ammonia is added and the mixture heated. The remainder is then gradually added, if necessary with the addition of ammonia, and finally more gelatin is added. The Specification as open to inspection under Sect. 91 includes also a further example in which separate solutions of silver nitrate, and of potassium bromide, potassium iodide, and gelatin are prepared, the former being stirred into the latter and the precipitate allowed to settle, the supernatent liquid being removed by decantation. The precipitate is then washed and divided into two parts, one of which is added to a solution of gelatin and ammonia. This is kept for 20 minutes at 50‹ C. and the other half then added together with more ammonia, the resulting mixture being stirred for 30 minutes at 50‹ C. and the remaining ammonia neutralized with citric acid. Reference is made to the use of citric acid for this purpose in examples 1 and 2. This subject-matter does not appear in the Specification as accepted.