184 METHODS IN PLANT HISTOLOGY 



weights and measures, these are so often the only ones given by makers 

 of plates and films that we have added them, often approximately, in 

 parentheses. Grains are in apothecaries' weight and ounces are in 

 avoirdupois. 



Developers for plates, films, lantern slides, and papers.— The fol- 

 lowing standard formulas can be recommended. Many others, some of 

 which may give better results for special cases, will be found in the 

 references at the end of this chapter. 



Metol-hydrochinon for lantern slides (Cramer). — 



A 



i\/r„t-;„ Apothecaries'- 



Metnc Avoirdupois 



Water 750 c.c. (25 oz.) 



Metol (or Pictol, Elon or other substitutes) 2 g. (30 gr.) 



Hydrochinon 6 g. (90 gr.) 



Sulphite of soda 30 g. (1 oz.) 



B 



Water 750 c.c. (25 oz.) 



Carbonate of soda 15 g. ( 5 oz.) 



Mix A and B in equal parts. This developer keeps well even when 

 mixed and can be used repeatedly. When fresh, add one drop of a 10 

 per cent bromide of potassium solution to each 30 c.c. of the de- 

 veloper. This is a good developer for lantern slides. 



Metol-hydrochinon for negatives and papers (Wall).— 



■j^ , . Apothecaries'- 



Metnc Avoirdupois 



Water 1,0(^0 c.c. (32 oz.) 



Metol (or substitutes) 2 . 25 g. (34 gr.) 



Sodium sulphite (dry) 45 g. (H oz.) 



Sodium carbonate (dry) 35 g. ( Ig oz.) 



Hydrochinon 4.7 g. (70 gr.) 



For negatives, dilute with an equal volume of water. For paper, 

 use 1 part to 3 parts of water and add 0.02 g. (about I gr.) of potassium 

 bromide to each 30 c.c. of the chluted developer. 



Cramer's Pyro-Soda for negatives. — 



A 



■««■ i. • Apothecaries'- 



Metno Avoirdupois 



Water 640 c.c. (16 oz.) 



Sodium bisulphite 4.5 g. (75 gr.) 



Pyrogallol 30 g. (1 oz.) 



