138 PHOTOGRAPHIC FACTS AND FORMULAS 
II. Potassium ferricyanide 40g 307 gr. 
Potassium oxalate 10¢g 77 gr. 
Glacial acetic acid 40 ccm 300 min. 
Water 1000 ccm 16 oz. 
If mixed in equal volumes, a reddish brown image is ob- 
tained; 1 part I and 2 parts II give a reddish image; 5 parts I 
and 1 part II give a brown. The colour is also dependent to 
some extent on the duration of the action of each bath. The 
negatives should be washed in a 2 per cent solution of citric 
acid, or 1 per cent oxalic or glacial acetic acid. If plain water 
be used, about five changes at intervals of 5 minutes are 
enough. Prolonged washing in running water will com- 
pletely remove the intensification, generally first in patches. 
Tue Leap INTENSIFIER.—This gives very great intensifi- 
cation and is only suitable for black and white line work: 
Lead nitrate 46¢ 353 gr. 
Potassium ferricyanide 70g 537 gr. 
Glacial acetic acid 20 ccm 154 min. 
Water 1000 ccm 16 oz. 
This will keep in the dark. The lead salts are rather tena- 
ciously retained by the gelatine; it is advisable to immerse the 
negatives in a 5 per cent solution of nitric acid for 5 minutes, 
and then wash. If the negative be subsequently developed, 
rather less intensification is given. By applying a 10 per 
cent solution of chromic acid to the bleached negative, an 
orange image is obtained, which is very non-actinic, and the 
lines remain clear. Treatment with a 2 per cent sodium 
sulphide solution gives the greatest increase. 
QUINONE INTENSIFIER (Lumiére)—This has not come 
into general use, and the intensification is practically depen- 
dent on a change of colour of the image into a more non- 
actinic one; but some compound of silver and bromine is 
present. 
