Dr. Eder has for a considerable time directed especial attention to the soda and potash developers, either of which seems to offer certain advantages over the ammoniacal pyrogallol. This advantage becomes particularly apparent with emulsions prepared with ammonia, which frequently show with ammoniacal developer green or red fog, or a fog of clayish color by reflected, and of pale purple by transmitted light. Ferrous oxalate works quite well with plates of that kind; so do soda and potassa developers.
For soda developers, Eder uses a solution of 10 parts of pure crystallized soda in 100 parts of water. For use, 100 c.c. of this solution are mixed with 6 c.c. of a pyrogallic solution of 1:10, without the addition of any bromide.
More pleasant to work with is Dr. Stolze's potassa developer. No. 1: Water, 200 c.c.; chem. pure potassium carbonate, 90 gr.; sodium sulphite, 25 gr. No. 2: Water 100 c.c.; citric, 1½ gr.; sodium sulphite, 25 gr.; pyrogallol., 12 gr. Solution No. 2 is for its better keeping qualities preferable to Dr. Stolze's solution. The solutions when in well stoppered bottles keep well for some time.

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