228 PHOTOGRAPHIC FACTS AND FORMULAS 
Water 1000 ccm 16 oz. 
Or the following (Eder) : 
Uranium nitrate 5¢ 38.5 gr. 
Ammonio-citrate or iron 5¢ 38.5 gr. 
Glacial acetic acid 200 ccm 314 oz. 
Water 1000 ccm 16 oz. 
CosaLt Toninc (Somerville) —Greenish or green-blue 
tones are obtained by this process, but they are very unsatis- 
factory. Bleach the image in: 
Potassium bichromate 60 g 460 er. 
Potassium ferricyanide 300 g 544 oz. 
Water 1000 ccm 16 oz. 
Then wash until free from any yellow stain, and immerse in: 
Cobalt chloride 25g 192 gr. 
Ferrous sulphate 6g 46 gr. 
Hydrochloric acid 200 ccm 3% oz. 
Water 1000 ccm 16 oz. 
Replacement of the hydrochloric by glacial acetic acid gives 
brighter green tones. The prints should be fixed in: 
Hypo 250 g 4 oz. 
Boric acid 45 ¢ 345 gr. 
Water 1000 ccm 16 oz. 
Dissolve by heat, and use when cold. Wash the prints well. 
Or bleach the image in: 
Potassium ferricyanide 60 g 460 er. 
Lead nitrate 40 ¢ 307 gr. 
Water 1000 ccm 16 oz. 
Wash thoroughly, and immerse in: 
Cobalt chloride 100 g 768 gr. 
Hydrochloric acid 30 ccm 230 min. 
Water 1000 ccm 16 oz. 
GoLp AND PLatinum ToninG (Somerville )—Gold toning 
is sometimes resorted to, more to improve the colour of prints 
