The ferrotype and how to make it - The Grian Press

86
THE FERROTYPF
CHAPTER VIII.
DEVELOPER AND DEVELOPMENT.
Froto-Sulphate of Iron as a Developei\
The developing solution, is nn aqueous solution
of iron with acid, and sometimes alcohol. The
form in which iron can be used as a developing
agent is that of a crystalized salt. This salt,
often termed copperas or green vitriol, is a sub-
stance formed in abundant quantities, and is used
for a variety of purposes in the arts. Commer-
cial sulphate of iron, however, being prepared on
a large scale, requires re-crystallization to render
it sufficiently pure for photographic purposes.
Pure sulphate of iron occurs in the form of
large transparent crystals, of a delicate green
color. By exposure to the air they gradually
absorb oxygen, and become rusty on the surface.
The sulphate of iron, colorless at first, afterward
changes to a red tint, and deposits a brown
powder. This powder is basic persulphate of
iron ; that is, a persulphate containing an excess
of oxide or base. By the addition of acetic acid
to the solution, the formation of a deposit is pre-
vented, the brown powder being soluble in acid
liquids