Various Methods of Development 381

fixing, gr, grm and soda

Page: 1 2 3 4 5 6 7 8

A slightly acidified amidol developer without any special addition may be used at tempera tures up to 80 F. and more, by reason of the very slight swelling of gelatine in acid baths. This developer may be adapted to temperatures up to 95 F. by the addition of sulphate of soda, as follows (L. J. Bunel, 1924) Soda sulphite, anhydrous 260 gr. (3o grm.) Potassium metabisulphite 90 gr. (so grm.) Amidol . . 45 gr. (5 grm.) Potassium bromide . 45 gr. (5 grm.) Lactic acid (officinal) . 50 min. (5 c.c.) Soda sulphate, cryst. . 2 oz. (ioo grm.) Water, to make 20 02. (1,000 C.C.) At higher temperatures than 95 F., sulphate of soda, even in larger amounts, no longer serves to prevent excessive softening of the gelatine, and part of the water normally used for making up the developer must be replaced by alcohol.

Whatever the developer employed, rinse the developed negative very rapidly, and proceed either with temporary " fixing," according to 375, or with fixing in a combined hardening and fixing bath ( 392. Combined Developing and Fixing. It is possible to carry out in a single bath the develop ment and fixing of a gelatino-bromide negative plate or film (gelatino-bromide papers cannot be treated in this way without the formation of heavy fog). This fact was known to W. D.

Richmond (1889). It is, however, only in recent years that it has been possible to obtain satis factory results in this way, and even then only in certain cases. For one thing, many emulsions, in order to give passable results by this method, must be given considerable over-exposure, and, for another, fixing and development are not influenced to the same extent by variations in temperature, the process of fixing being retarded by cold and accelerated by heat more than is the case with development (C. E. K. Mees, 1921). This causes heavier development to occur in cold baths than in hot.

Improving on the methods due to C. Otsuki and T. Sudzuki (1914), and to L. J. Btmel (1921), A. and L. Lumiere and A. Seyewetz (1924) recommended the following bath, in which development and fixing are completed in 15 to 20 minutes at a temperature between 60 F and 65 F. (About 2 oz. of the solution are required for a quarter-plate.)- Soda sulphite, anhydrous 350 gr. (40 grm.) . mid ol . 45 gr. (5 grm.) Soda phosphate, tribasic . i75 gr. (20 grin.) I Iypo . . oz. (25 grin.) Water, to make . . 20 OZ. (1,000 c.c.) When the solution has been once used it must be thrown away.

Page: 1 2 3 4 5 6 7 8