ELEMENTARY PHOTO-MICROGRAPHY. 47 



reds. It is well to use both and have a variety of 

 colours. 



Backed plates give better negatives, but are 

 messy, so, until the worker gains experience, it is 

 better for him to commence with the unbacked 

 plates. 



For negatives of any kind nothing beats the pyro 

 soda developer. 



No. i, or A. 



Pyrogallic acid ... ... 60 grains 



Potassium metabisulphite ... 15 

 Water ... ... ... 10 ounces 



No. 2, or B. 



Washing soda ... ... i ounce 



Sodium sulphite ... ... i 



Water ... ... ... 10 ounces 



Four drams of A and four drams of B, with five 

 drops of ten per cent, solution of potassium bromide, 

 are taken for a quarter-plate. 



For lantern slides I find that hydrokinone is 

 the most generally convenient. It may be made 

 up as follows: 



A. 



Hydrokinone . . ... 80 grains 



Potassium bromide ... ... 15 



Sodium sulphite ... ... i ounce 



Water ... ... ... 10 ounces 



