THE, TRON) PROCESSES 269 
Cobalt carbonate 8g 61.5 gr. 
Effervescence takes place, and the mixture should be digested 
until it turns red. The cobalt carbonate can be made by 
adding 39 g (299.5 gr.) crystallised sodium carbonate to 16 g 
(123 gr.) of crystallised cobalt chloride, and washing and 
drying the precipitate. To the above red liquid, cooled down 
taro: (95°F .), add: 
Lead peroxide ~ 5¢g 38.5 gr. 
Glacial acetic acid. 3 ccm 23 min. 
On shaking, the solution turns a deep green. From this point 
all further operations must be conducted by yellow light. 
Add: 
Lead peroxide 5g 38.5 gr. 
Glacial acetic acid 3 ccm 23 min. 
Pour the solution out into a flat dish, and allow to evaporate 
until crystals form and it is dry. Add 10ccm (77 min.) of 
water, filter, and make the bulk up to 1000ccm (160z.). 
The iron salt is obtained by mixing 20g (154 er.) of ferric 
sulphate with ammonia, washing the precipitate, and adding 
36 g (276.5 gr.) of acid ammonium oxalate. This can be 
made by adding 30ccm (230min.) of ammonia to 100g 
(768 gr.) of oxalic acid, gently heating, adding more am- 
monia until the solution smells distinctly of ammonia, then 
heating to drive off excess of ammonia, adding 100¢ 
(768 gr.) of oxalic acid, heating until dissolved, and allowing 
to crystallise. The actual sensitising solution is made by 
mixing 2 parts of the cobalt solution with 1 part of the iron. 
Paint on the paper with a brush and dry rapidly; the paper 
should be a green colour. Exposure may be to daylight or 
an arc, and the image should show a bright yellow on the 
green ground. Development is effected in a 1 per cent solu- 
tion of potassium ferricyanide until the whites appear white; 
then briefly wash and immerse in 1 per cent hydrochloric 
