146 Methods in Plant Histology 



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 formulae, 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. ( f oz.) 



Glacial acetic acid (10 per cent solution) . . 148 c.c. (5 oz.) 



The following gives a more greenish-blue tint : 



Metric Apothecaries 



Uranium nitrate (10 per cent solu- 

 tion in water) 3.6 c.c. (1 dram) 



Ferric ammonia citrate (10 per cent 

 solution in water) 3.6 c.c. (1 dram) 



Potassium ferricyanide (10 per cent 



solution in water) 7.2 c.c. (2 drams) 



Nitric acid (10 per cent solution in 

 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. 



Green Tones. 



A. Potassium bichromate (10 per 



cent solution in water) 60 drops 



Potassium ferricyanide (10 per 



cent solution in water) 30 c.c. ( 1 oz.) 



Water 120 c.c. ( 4 oz.) 



B. Cobalt chloride 3.9 g. (60 gr.) 



Ferric sulphate. 3.9 g. (60 gr.) 



Hydrochloric acid 15 c.c. ( ^ oz.) 



Water 120 c.c. ( 4 oz.) 



Bleach in A, wash 10 minutes in water, tone in B, and then 

 wash 20 minutes in water. 



