GB642616A - Improvements in metal salt precipitation inhibitors - Google Patents

Abstract

A metal precipitation inhibitor for incorporation in an aqueous solution comprises a dry mixture of an alkali metal phosphate other than an orthophosphate (e.g. sodium hexametaphosphate, potassium pyrophosphate, or sodium tetraphosphate) and a polyhydroxycarboxylic acid (e.g. tartaric, gluconic, mucic, ascorbic, saccharic, or gallic acid) or an alkali metal salt thereof. The prevention of the precipitation of calcium and aluminium salts is referred to. The production of tackiness in solid mixtures may be prevented by the admixture of an inert alkali metal sulphate, e.g. anhydrous sodium or potassium sulphate. In example 1, sodium hexametaphosphate and gluconic acid are added to an aqueous photographic developing solution containing monomethyl-p-aminophenol sulphate, hydroquinone, sodium sulphite, and borax. In example 2, sodium tetraphosphate and sodium mucate are added to the same developing solution. In example 3, tetrapotassium pyrophosphate and saccharic acid are added to an aqueous photographic developing solution containing monomethyl-p-aminophenol sulphate, hydroquinone, sodium sulphite, sodium carbonate and potassium bromide. In example 4, sodium tetraphosphate, gallic acid and calcium chloride are added to the developing solution of example 3. In example 5. a solution for treating photographic films prior to drying contains water, ethyl alcohol, di-octyl sulphosuccinate, sodium tetraphosphate and sodium gluconate. In example 6 a two-powder dry photographic developing mixture contains in one powder monomethyl-p-aminophenol sulphate and hydroquinone and in the other powder sodium sulphite, sodium carbonate (both anhydrous), potassium bromide, sodium tetraphosphate and sodium gluconate.