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Original Articles

Some Aspects of Developer and Fixing Bath Concentrates Based on Potassium and Ammonium Salts RespectivelyFootnote

Pages 44-47 | Received 03 Sep 1965, Published online: 23 Jul 2016
 

Abstract

The limited solubility of some potassium salts in comparison to corresponding sodium salts is known from analytical chemistry; the analytical behaviour of ammonium salts is similar to that of potassium salts.

On the other hand, potash and potassium sulphite which are of interest for photographic developers ore several times as soluble as soda and sodium sulphite. Most developer concentrates, therefore, contain potassium salts. However, certain processing conditions may lead to turbidity or precipitation in the developers, due to the formation of sparingly soluble potassium hydroquinone disulphonate.

Commercial fixing bath concentrates contain ammonium thiosulphate which is much more soluble than sodium thiosulphate. Potassium thiosulphate is only slightly more soluble than sodium thiosulphate and, moreover, proves useless as a fixing agent. Fixing baths on the basis of ammonium thiosulphate are superior to those based on the corresponding sodium compound in the processing of films containing silver iodide.

In practical use the formation of crystalline deposits containing ammonium, silver, iodide and thiosulphate ions may occur.

Notes

Paper presented at the Symposium on “Processing Technology”, organized by the Science Committee on 12-14 May 1965, in London.

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