FERROUS OXALATE.
This developer is still recommended for bromide paper. It gives good blacks, but there is danger of staining if it is carelessly used. Novices do not usually succeed with it. It has the further disadvantage that the iron must be dissolved out, and the acid removed, before fixing, or fading will result. No. 1 : Potassium oxalate, 4 oz. ; water, 10 oz. No. 2: Ferrous sulphate, 5 oz. ; water, 10 oz. ; acetic acid, 10 drops. For use, take 6 parts of No. 1 and 1 part of No. 2, and add 4 drops of a 10 per cent. solution of potassium bromide. In mixing these, it is essential that the ferrous sul phate should be poured into the oxalate, not the oxalate into the iron. The rea son for this is that when ferrous sul phate mixes with potassium oxalate there is formed ferrous oxalate, a yellowish insoluble compound — which, however, is soluble in excess of potas sium oxalate. Thus, if the oxalate is poured into the iron, the result is a dirty yellow mud, whilst if the iron is poured into the oxalate a clear red solution is formed, as the potassium oxalate is all the time in excess of the iron. The prints must be placed direct from the developer in a bath of acetic acid (or citric or sul phuric acid may be used), strength 1 in 200.
The developer may be used repeatedly, but gives harder results as it becomes old. It may be reconverted to its original state by standing it in the sun, the ferric oxalate being thus changed once more into ferrous oxalate. Another developer is: Glycin, 10 parts ; sulphite of soda, 30 parts ; carbon ate of potash, 56 parts ; water, 750 parts.
A:uinoL.
_Another favourite developer among some workers. It gives results very similar to metol, and may be used quite fearlessly even by those whose skins are affected by the action of metol. The peculiarity of this developer is that it does not need the assistance of an alkali to reduce the silver. The simplest method of using this is to take any desired quantity of the 10 per cent. solution of soda sulphite already made up for ordinary plate development, and to add 3 grs. of amidol and 1 grain of potassium bromide to each ounce. Potas sium bromide is not capable of restraining to the same extent as usual with this developer.