REDUCERS 147 
the rapidity of action desired. Immersion in a 5 per cent 
solution of sodium sulphite has been recommended as a stop 
bath, but this is liable to cause red stains. The best plan is to 
wash rapidly. 
The following mixture (Puddy) acts on the shadows be- 
fore the high-lights: 
Ammonium persulphate 50 g 384 gr. 
Ammonium sulphocyanide 25 g 192 er. 
Water 1000 ccm 16 oz. 
The following solution acts on all densities nearly alike: 
A. Potassium permanganate 0.25 g 1.92 gr. 
Sulphuric acid, 10% solution 15 ccm 115 min. 
Water 1000 ccm 16 oz. 
B. Ammonium persulphate 25'e 192 gr. 
Water 1000 ccm 16 oz. 
For use mix 1 part A with 3 parts B. The separate solutions 
keep well, but should not be mixed until required. The time 
of reduction varies from 1 to 3 minutes, and greater control 
is obtained by diluting the mixture with an equal volume of 
water. As soon as the desired reduction is reached, immerse 
the negative in a 1 per cent solution of potassium metabisul- 
phite for 5 minutes, and wash. 
QUINONE REDUCER (Lumiére).—This acts like ammonium 
persulphate, that is, reduces the high-lights more than the 
shadows: 
Quinone 5g 38 gr. 
Sulphuric acid 20 ccm 154 min. 
Water 1000 ccm 16 oz. 
As soon as the desired reduction is reached, the plate should 
be immersed in a 2 per cent solution of sodium bisulphite, 
washed, and dried. 
Harmonisinc Harsu Necatives.—This method of re- 
ducing the over-dense parts of negatives has been replaced by 
