REDUCERS 145 
Enough acid should be used to dissolve the precipitate. To 
the clear solution add: 
Ammonia q.S. 
This forms a deep blue, clear solution to which should finally 
be added: 
Hypo 5¢g 38 gr. 
Water to 1000 ccm 16 oz. 
This is said to be particularly useful for local reduction of 
prints. The print should be well soaked in water, placed 
face up on a sheet of giass, and the reducer applied with a 
pad of absorbent cotton. The action is at once stopped by 
well washing with water. This has been but little used in 
practice, and the method of making is a roundabout way of 
making cupric chloride. An easier way would be to mix: 
Cupric sulphate 5) g 38 gr. 
Salt 2.35 g 18 gr. 
Water 100 ccm 2 02. 
then add enough ammonia to form a clear solution. 
Ferric chloride and sulphate either alone or with citric acid 
have been recommended as reducers; but they are extremely 
liable to stain the gelatine by the deposition of basic iron salts 
and should not be used. 
Hypo AND FERRICYANIDE (Farmer ).—This is prepared as 
wanted by adding a little 10 per cent solution of potassium 
ferricyanide to a 20 per cent plain solution of hypo. The 
quantity of ferricyanide to be added depends on the result 
desired; the weaker the solution, the more even the action, 
that is to say, the less the shadows are attacked. A pale 
yellow coloured mixture is best. The colour of the solution 
rapidly disappears in use, and this is a sign of exhaustion. A 
fresh mixture should be applied rather than allow an old one 
to act. The action of this bath is the conversion of some of 
