264 PHOTOGRAPHIC FACTS AND FORMULAS 
heat. Filter the mixture through fine linen. Or the follow- 
ing may be used: 
Gum arabic 100 g 768 gr. 
Ferric chloride 328 g 2519 gr. 
Tartaric acid 220 g 1690 gr. 
Ferric sulphate, basic 220 ¢ 1690 gr. 
Water 1000 ccm 16 oz. 
Dissolve in the above order and filter. The following (Fisch) 
is only suitable for heavily sized or gelatinised papers: 
Ferric chloride 100 g 768 gr. 
Water 500 ccm 8 oz. 
Dissolve, and add: 
Tartaric acid 30 g 230 gr. 
Water 500 ccm 8 oz. 
Or the following (Shawcross) may be used for any paper: 
Gelatine 137 ¢ 1052 gr. 
Ferric sulphate, basic 55 ¢ 422 gr. 
Sodium chloride 87 g 668 gr. 
Tartaric acid I7¢g 130 gr. 
Ferric chloride 137 g 1052 er. 
Water 1000 ccm 16 oz. 
The solutions should be applied with a broad flat brush or 
pad by artificial light, and rapidly dried. The paper will keep 
for 2 or 3 weeks. Exposure should be made under a drawing 
for about 10 minutes in sunlight, or until the lines appear 
yellow on a white ground. Development is effected on: 
Gallic acid 6g 46 gr. 
Oxalic acid lg 77 gr. 
Water 1000 ccm 16 oz. 
Or: 
Gallic acid 1252 96 gr. 
Alum 125g 96 gr. 
Water 1000 ccm 16 oz. 
