Development in the Dark Room. 23 
DEVELOPMENT IN THE DARK ROOM. 
piven dies (B. COLLiERs 
(Read before the Photographic Section of the Society, March 17, 1890.) 
(ABSTRACT. ) 
THERE is nothing in the whole range of photography, about 
which so much has been said and written as this subject of devel- 
opment, and I recognize at the outset the difficulty I shall experi- 
ence in interesting you. What I shall say, however, will be 
denuded of all technicalities, and presented in the plainest lan- 
guage possible, so that the youngest members here can not fail to 
understand my meaning. 
As you all know, the dry plate, in whatever fern we find it, is 
simply a gelatine emulsion, of which the bromide of silver is the 
principal ingredient, supported by a backing of glass, paper, cellu- 
loid, or what not. The action of the light upon this emulsion pre- 
Cipitates the bromide of silver in quantities directly proportionate 
to the intensity of the light; and the subsequent treatment of the 
plate by the developer, and the reduction of unprecipitated 
bromide of the hypo-solution, produces that condition which is 
termed negative. Now in the reduction of the silver bromide two 
agencies are employed—an acidand an alkali. I shall not attempt 
an explanation of the chemical changes that take place during the 
development of a plate, but confine my remarks to the results 
obtained so far as 1 am acquainted with them. The action of the 
developer, or rather the action of the two principal ingredients, 
acid and alkali, has been very correctly likened to the relation that 
may be said to exist between generated steam as a motive force, 
and the machinery by which that force is intelligently applied to 
the movement of a body, the alkali corresponding to the steam, 
and the acid to the machinery, by which the force of the former is 
directed. Bearing this i!lustration in mind, it is easy to understand 
that there is a fixed relationship of alkali to acid, and if the proper 
proportion of one to the other is varied from, the effectiveness of 
the developer is reduced in a corresponding degree. 
Beginning with the first developer I ever used, and which [| 
found to be the simplest, I would call attention to the ferrous 
