188 METHODS IN PLANT HISTOLOGY 



emulsion and does not stain. Plates should be left in the bath for 15 

 minutes after the silver seems to have been dissolved. 



Short-stops. — After development, a plate, film, or paper should be 

 rinsed in water or, preferably, in a short-stop before going into the 

 hypo. Enough acetic acid added to the rinsing water to give it the 

 taste of weak vinegar will stop the development immediately and will 

 save the hypo. If the acetic acid is too strong, it will cause pimples on 

 the emulsion. Small blisters are often caused by a direct transfer from 

 the developer to the hypo. 



Hardener for plates and films. — In the tropics, and in warm weather 

 anywhere, it is desirable to harden the emulsion. 



Metric Avoirdupois 



Water 300 c.c. (10 oz.) 



Chrome alum (granular) 30 g. (1 oz.) 



After development, transfer to the hardener without previous rinsing 

 in water and rock for 15 seconds; then transfer directly to the hypo. 

 The hardener may be used repeatedly. Even if washing must be done 

 in water at 80° or 85° F., the emulsion will not be damaged after treat- 

 ment with this hardener. 



Sepia tones. — Hypo must be washed out thoroughly before bleach- 

 ing. 



Stock Bleaching Solution Stock Toning Solution 



Metric Avoirdupois Metric Avoirdupois 



Potassium bromide ... . 30 g. (loz.) Sodium sulphide 30 g. (1 oz.) 



Potassium ferricyanide . 90 g. (3 oz.) Water 300 c.c. (10 oz.) 



Water '. 300 c.c. (10 oz.) 



Bleach in 1 part stock bleaching solution to 9 parts water until the 

 print is light brown. Rinse in water 1 minute. Tone in 1 part stock 

 toning solution to 20 parts water. There is no danger in prolonging 

 either bleaching or toning. Wash as thoroughly as after hypo. 



Sepia tones may be obtained by bleaching in a saturated solution 

 of bichloride of mercury with 3 drops HCl to 30 c.c. (after hypo has 

 been washed out) ; washing in water and toning in 1 part ammonia to 

 10 parts water. Wash thoroughly. 



MISCELLANEOUS HINTS 



1. Keep all chemicals in a dark, cool, dry place. 



2. Keep bottles tightly stoppered and packages tightly closed. 



3. Store ammonia, sodium sulphide, and ammonia sulphide away from the 

 rest of the chemicals. 



