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430 Transactions of S.M.P.E., Vol. XIII, No. 38, 1929
The four curves, A, B, C, and D (Fig. 6) show that 160 feet of film can be processed satisfactorily per gallon of borax developer if it is properly revived at intervals. The revived developer gives the same gamma in a given time of development as the original developer while the emulsion speed at this exhaustion point is fully 60 per cent of the original.
Tests were made by adding increasing quantities of potassium bromide to a fresh developer and measuring the speed loss. It was found that about 1.5 grams per liter of potassium bromide were required to reduce the speed of the emulsion to 60 per cent of its original value. This content of potassium bromide corresponds with the quantity of bromide present in the exhausted developer as determined by analysis. The quantity of potassium bromide present was determined as follows: The sodium sulfite and developing agents were oxidized in alkaline solution with sodium peroxide and ammonium persulfate. After acidifying, the bromide was precipitated with excess silver nitrate and the excess silver titrated with potassium thiocya.nate wath ferric nitrate as an indicator. This analysis showed a content of 1.6 grams of potassium bromide per liter in a developer exhausted with 200 feet of film per gallon.
Also a determination of the quantity of bromide liberated in the developer calculated from the quantity of silver left in the developed negative shows that the equivalent of from 1.0 to 2.0 grams of potassium bromide are liberated after developing 200 feet of film per gallon, depending approximately upon the integrated density of the negative.
B. Sludging Properties of the Developer.
Sludging is a normal and unavoidable characteristic of the borax developer. The sludge is made up mostly of finely divided silver and imparts to the developer a light gray muddy appearance. An analysis of dried sludge from a used developer w^hich contained all the foreign matter which accumulated during the processing of 160 feet of film per gallon indicated a content of 40 per cent pure silver.
With the rack and tank method of development where a tank of developer is used over a period of two weeks or longer the developer contains a considerable quantity of sludge after 160 feet of film per gallon have been processed. In the experience of this laboratory the quantity of sludge which forms has never been sufficient to interfere with successful development.