Il8 PRACTICAL PHOTO-MICROGRAPHY. 
gradually, till no further action appears to take place. 
If experience tells us that the development has not at 
this juncture gone far enough, we add, say, io mins, 
more of the ammonia solution. When development is 
complete the plate is well washed and placed in the 
fixing solution. 
In place of ammonia, one or more of the alkaline 
carbonates may be used as the alkali, and many workers 
prefer the carbonates. Bromide, in the case of such 
a developer, may be omitted, or present in minute 
quantity, the following representing a good average 
developing solution : 
Pyrogallol (30 mins, of the stock solution 
with sulphite given above, or ... ... 3 grains 
Potassium or sodium carbonate of soda, or 
both, in equal parts ... ... 16 ,, 
Potassium bromide (nil, or) ... ^ grain. 
Water to ... ... ... ... ... 1 ounce. 
This will develop a plate rather more slowly than 
pyro-ammonia; it is little apt to produce green fog, and 
good contrast and density can be obtained. The him 
is likely to be stained yellow, but the acid alum bath 
(page 111) will remove the stain in a short time. 
If the details rush up quickly under the pyro- 
ammonia developer, and if density does not increase 
at a rate commensurate with the details, the plate has 
been over-exposed, and we may add bromide to the 
developer ; this will check the detail considerably, the 
density less. If, on the other hand, neither detail nor 
density come up readily, we may add ammonia; if 
density comes in some parts, and the other parts lack 
