DEVELOPMENT OF PLATE. 79 
resulting solution of oxalate of iron should be of 
a rich ruby color and free from precipitate. 
It is best to mix the developer in a wide- 
mouthed glass vessel, so that it may be poured 
over the plate at a single sweep. A small 
tumbler or a wide-mouthed bottle having a 
capacity of from two to four ounces will answer 
very well. If the smallest-sized plates (23X34) are 
used, an ounce of the developer will be a sufficient 
quantity to mix at one time, and this may be used 
to develop several plates in succession. The iron 
solution must always be added to the oxalate. If 
it be in too small quantity, the development will 
be slow and imperfect; if in too great quantity, 
a yellow precipitate will be deposited upon the 
plate. 
The developing-tray may be of hard rubber, porce- 
Jain, or glass. A cheap oblong glass dish with 
flat bottom answers very well for quarter-size 
plates (344+). It must be kept scrupulously 
clean. In general it may be said that in pho- 
tographic operations every solution used should 
have a receptacle which is devoted to its sole 
use. 
The developer must thoroughly cover the plate, 
and if any air-bubbles are to be seen which cannot 
be removed by gently tipping the developing-tray 
forward and back, they should be removed with 
a soft camel’s-hair brush. 
The image does not appear as quickly upon a 
dry plate as upon a wet one, as some little time is 
required for the solution to penetrate the film; 
