262 PHOTOGRAPHIC FACTS AND FORMULAS 
B solution 80 parts 
C solution 50 parts 
It is important to adhere to this order, for, if A be added to 
C, the mixture becomes lumpy and useless. The mixture is 
at first thin and fluid, but soon becomes more viscous, and in 
a few hours cloudy and of the consistence of soft butter. It 
should be used in this condition and will keep in the dark for 
several days. Haugk recommended: 
Gum arabic solution, 1:5 300 to 350 parts 
Ammonium ferric oxalate solution, 6:10 100 parts 
Ferric chloride solution, 1:2 20 to 30 parts 
Float the paper on this mixture. Another excellent formula 
(Waterhouse) is: 
A. Gum arabic 170g 6 oz. 
Water 650 ccm 22 oz. 
B. Tartaric acid 40 ¢ 617 gr. 
Water 150 ccm 5 oz. 
C. Ferric chloride solution, 
sp. gr. 1.453 100 to 120 g 1543 to 1851 gr. 
Filter the gum solution through a sponge or pad of cotton, 
and mix with the acid; then add the iron solution, which 
should be weighed, not measured, with constant stirring. 
Allow the mixture to stand in the dark for 24 hours, and add 
water to make the specific gravity 1.100. Well-sized paper, 
preferably gelatine-sized, should be fastened by pins to a 
flat board, and the mixture applied not too thickly with a flat 
brush. As soon as the brush begins to drag, the coating 
should be evened out with a round brush with circular strokes. 
This operation should be performed by artificial light, and 
the paper rapidly dried in the dark. The paper should be 
kept under pressure. The exposure will be from 15 to 40 
seconds in the sun, or proportionately longer in diffused 
