The ferrotype and how to make it - The Grian Press

THE DARK ROOM. 55
water-tight. After a day's work, if the tank is
full, a small quantity of a saturated solution of
copperas (the commonest salt of iron) should be
thrown into the tank, for the purpose of precip-
itating the silver that may be in the water. It
should be left all night, to allow time for the pre-
cipitate to fall to the bottom. In the morning the
stop-cock should be turned and the water allowed
to run off, which it will do readily, the waste-
pipe acting as a syphon. It will be necessary,
however, that the tank should be full of water,
or at least that the water should be above the
top of the waste-pipe, in order that it may run
out, for the water must be high enough to flow
through the pipe when the stop-cock is turned,
after which it will continue to run until all is
exhausted. A tank arranged as thus described
is the best silver-saving apj)aratus that can be
devised. It receives all the washings of the
plates, all the waste of the developing and fixing
solutions, all the silver solution that may be wasted
from the bath dish in raising the dipper many
times a day, all the drippings of plates, all the
films which should be rubbed from rejected plates
or off the edges of all plates after development.
These are all readily precipitated by the solution
of iron, which costs but a trifle by the quantity.
The precipitate, which is a thick black mud, may
be taken from the tank once a year, or oftener if
the business is large, and given to competent
men for the reduction and separation of the sil-
ver it may contain.