270 PHOTOGRAPHIC FACTS AND FORMULAS 
acid; again wash and immerse in a 1: 400 solution of sodium 
sulphide until the paper turns grey; then wash until white. 
The sensitised paper will only keep about 6 hours. If the 
ordinary ferric oxalate be used, the process is said to be 
suitable for ordinary negatives. 
KALLITYPE.—This is a silver-iron printing process, based 
on the light-sensitiveness of ferric salts, which are reduced 
to the ferrous state. The ferrous salts dissolve in the devel- 
oper, and reduce silver nitrate to the metallic state at the 
points where the ferric salt has been reduced by light. 
Hall’s Formulas.— 
A. Ferric oxalate 200 g 1 oz. 
Gum arabic 20 g 48 er. 
Water 1000 ccm 5 oz. 
B. Ferric potassium oxalate 62.5 g 4 02. 
Water 1000 ccm 8 oz. 
C. Oxalic acid 125 ¢ 4 oz. 
Ammonia 52 ccm 100 min. 
~ Water 1000 ccm 4 oz. 
D. Potassium bichromate 62.5 ¢ 120 er. 
Water 1000 ccm 4 oz. 
For use mix 480 parts A, 240 parts B, 30 parts C, and 4 parts 
D. Then add silver nitrate, dry, 37.5 parts. For thin and. 
soft negatives, increase the proportion of D from 30 to 50 
per cent, and reduce the proportion of C by one-half or more. 
Developer : 
Sodium acetate 125 ¢ 1 oz. 
Tartaric acid 3/123i¢ 12 or. 
Solution D, above 5to50ccm 10to 100 min. 
Water 1000 ccm 8 oz. 
Clearing bath: 
Sodium citrate 31.25 ¢g ¥4 oz. 
Citric acid 5g 20 gr. 
