158 
METHODS IN PLANT HISTOLOGY 
thoroughly; fix and wash as usual; then tone in the following 
solution: 
A. Potassium ferricyanide 
Water. 
B. Copper sulphate. 
Potassium citrate. 
Water. 
Metric 
Apothecaries’ 
6 g. 
( 90 gr.) 
295 c.c. 
( 10 oz.) 
7g. 
( 110 gr.) 
65 g. 
(1,000 gr.) 
295 c.c. 
( 10 oz.) 
(The metric and U.S. measures are practically rather than arithmetically 
equivalent.) 
When needed for use, pour some of A into an equal quantity of 
B, stirring or shaking constantly. Put the slide into the solution in a 
tray and rock just as if developing a plate. The solution is a strong 
reducer. The tone should change from black to warm, then to sepia, 
and may finally become quite red. The time may vary from 1 to 20 
minutes, according to the density of the slide and the tone desired. 
The finished product must not be too dense, for a slide, toned in this 
way, may seem rather weak and yet appear surprisingly strong 
on the screen. 
After toning, wash in water for about 20 minutes. 
Moonlight Tints. —Some excellent formulas, recommended by 
Anderton, will be of service: 
Metric Apothecaries’ 
Ferric ammonia citrate (10 per cent solu¬ 
tion) . .. 15 c.c. (| oz.) 
Potassium ferricyanide (10 per cent solu¬ 
tion) . 15 c.c. (£ oz.) 
Glacial acetic acid (10 per cent solution) 148 c.c. (5 oz.) 
The following gives a more greenish-blue tint: 
Uranium nitrate (10 per cent solu- 
tion in water). 
Ferric ammonia citrate (10 per cent 
3.6 c.c. 
(1 dram) 
solution in water). 
3.6 c.c. 
(1 dram) 
Potassium ferricyanide (10 per cent 
solution in water). 
Nitric acid (10 per cent solution in 
7.2 c.c. 
(2 drams) 
water). 
7.2 c.c. 
(2 drams) 
Both solutions intensify considerably, so that slides to be toned 
should be rather weak. After toning, wash 20 minutes in water. 
