176 PHOTOGRAPHIC FACTS AND FORMULAS 
Add: 
Yellow resin 4g Jl ee 
Then heat the mixture until the resin is dissolved, adding 
more ammonia if necessary. Allow to cool, and add: 
Gelatine 4g 31 gr. 
Water 40 ccm 307 min. 
Neutralise with hydrochloric acid, and add saturated solu- 
tion of citric acid until the mixture has a distinct acid reac- 
tion. This should be added to the emulsion, allowance being 
made for its bulk by reducing the quantity of water used in 
making up the emulsion. 
To obtain hard, contrasty printing papers, add to any of 
the above emulsions from 0.7 to 3.5 per cent of the following 
solution : 
Chromic acid 25¢g 192 gr. 
Water 100 ccm 770 min. 
When dissolved, add: 
Calcium carbonate, pure q.s. 
with constant stirring until the mixture remains turbid, then 
filter, and wash the filter with: 
Water to make 250 ccm 4 oz. 
This forms approximately a 10 per cent solution of calcium 
chromate. The more of this is added to the emulsion, the 
harder it works. 
PRINTING should be carried on until the high lights show a 
decided tinge; then the prints should be immersed in: 
Salt 100 g 114 oz. 
Sodium carbonate, dry 50 g 3% OZ. 
Water 1000 ccm 16 oz. 
Bathe for 5 minutes, rinse for 5 minutes, and tone. 
TONING may be effected either with an alkaline, a sulpho- 
cyanide, or a combined bath. The first-named does not give 
