324 PHOTOGRAPHIC FACTS AND FORMULAS 
Sodium nitrite 10g 154 gr. 
Filter into an ice-cold dish. Paper should be floated on the 
cold solution, or fabric immersed, wrung out, and dried in 
the dark. Exposure under a negative will be from 8 to 12 
minutes in diffused light, and the image shows in a brown 
colour on the yellow ground. Development should be effected 
with a 10 per cent solution of fused sodium acetate, which 
gives brownish-red tones. If alpha-naphthylamine be used, 
brownish-grey tones are obtained. Better colours are ob- 
tained by adding a little of the sensitising solution to the 
developers. The prints should be subsequently washed, and 
dried. 
Schoen patented the use of diazotised ortho-amido-salicylic 
acid and its compounds for obtaining coloured prints on paper 
and fabrics, red tones being given, which can be altered by 
treatment with various compounds, such as ferric chloride, 
lead acetate, cobalt nitrate, lime or baryta water. 
