PYROLIGNEOUS ACID Crude acetic acid.
(See " Developers, Mixed or Combined.") Dr. Eder and others have recommended the use of the alkali potash to take the place of ammonia or soda in the developer. Several advantages have been claimed for itnamely, the stable nature of the alkali and its freedom from fog or stain, but its drawbacks are slow working and possibility of frilling. The average of the many formula: advocated is : Pyro . . . 3o grs. 7 g.
Potassium carbonate . 120 28 ,y Water . . . 10 oz. I,000 ccs.
Bromide is added as required.
Eder's formula is in a two-solution form, and is much as follows : A. Pyro . . . 436 grs. zoo g.
Sodium sulphite 1,o90 25o Sulphuric acid . Io mins. 2 ccs.
Water . . . To oz. I,000 B. Potass. carbonate 2,000 grs. 46o ccs.
Sodium sulphite . 55o 126 Water . . . 10 oz. i,000 ccs.
For use, add 135 drops of eaeh to io oz. of water. There are many other formula:.
A developer that is popular on account of soda having many advantages over ammonia, which in 1862 was introduced as an accelerator for pyro. Washing soda is largely used in place
of crystallised sodium carbonate, but the latter should always be used when sodium carbonate is mentioned. This developer gives off no fumes as ammonia does, and may therefore be used with greater comfort ; it rarely produces, chemical fog, and negatives properly developed are of a good printing colour.
The average of twelve of the best-known. formula: is : Pyro . . . 3o grs. 9 g.
Sodium sulphite . 240 >, 55 >, Sodium carbonate 240 ,y 55 >, Water to . . . io oz. i,000 ccs.
Some workers prefer to make up the developer except the pyro, and add the latter just before use. Lange's (which see) is typical.
The Hurter and Driffield standard pyro-soda. developer for plate-speed testing is : Pyre . . 8 parts.
Sodium carbonate (crys.) . 4o Sodium sulphite . )7 Water to . . . . i,000 This should be used at a temperature of 65° P. (i8° C.).