156 
METHODS IN PLANT HISTOLOGY 
Warm Tones.—A pyro-ammonia developer for warm tones is 
recommended in Harrington’s Photographic Journal for June, 1914: 
Metric Apothecaries’ 
A. Pyro. 
... 31 
g- 
(1 oz.) 
Sodium sulphite crystals.... 
... 62 
g- 
(2 oz.) 
Citric acid. 
... 2.6 g. 
(40 g.) 
Water. 
... 237 
c.c. 
(i pt.) 
B. Ammonia. 
... 31 
g- 
(1 oz.) 
Water... 
... 237 
c.c. 
(J Pt.) 
C. Ammonia bromide. 
... 31 
g. 
(1 oz.) 
Water. 
... 237 
c.c. 
(2 pt.) 
solutions A, B, and C keep well separately, 
but not when 
mixed. When wanted for immediate use, mix A, 1.8 c.c. (30 minims), 
B, 3.7 c.c. (60 minims), and C, 1.8 c.c. (30 minims), and add 30 c.c. 
(1 oz.) of water. 
A correctly exposed plate will develop in about 2\ minutes, and 
the tone should be a warm black. Brown tones are secured by 
increasing the quantity of C, while A and B remain the same. 
Reducing Overexposed Negatives and Lantern Slides.—In case 
of overexposure, the negatives or lantern slides can be saved by 
reducing. The reducing solution should be applied as soon as the 
negative is well fixed in hypo. If a negative which has been washed 
and dried is to be reduced, it should be soaked in water for half an 
hour before using the reducing solution. 
The following is a good solution for most purposes: 
Metric Apothecaries’ 
^ ( Water.. 473 c.c. (16 oz.) 
\ Hyposulphite of soda. 31 g. ( 1 oz.) 
g ( Water. 473 c.c. (16 oz.) 
\ Red prussiate of potassium. 31 g. (1 oz.) 
Solution B must be protected from the light. Cover the bottle 
with black paper and keep it in the dark when not in use. 
Mix only for immediate use 8 parts of A to 1 of B and use in rather 
subdued light. A darkroom is not necessary, but avoid bright 
light. 
When the negative or lantern slide becomes satisfactory, wash 
it in water as thoroughly as if it had just come from the ordinary 
hypo fixing solution. 
