The ferrotype and how to make it - The Grian Press

DEVELOPEE AND DEVELOPMENT. 87
The action of sulphate of iron upon the nitrate
of silver solution is to change its character by
convertino^ the silver of the solution to a metallic
state, in which state it is deposited in the form of
a grayish powder, the character of the deposit
being somewhat aifected by the acid.
Various acids are used in the developing so-
lution. The most prominent are acetic, glacial
acetic, nitric, citric, gallic, and pyrogallic acids.
The last three, however, are more used in the
process of re-development of negatives. The
first is, for many reasons, the best, and is gen-
erally used in solutions for the primary develop-
ment of negatives and always for positives.
Acetic acid is a product of the oxydation of
alcohol. Spirituous liquors when perfectly pure
are not affected by exposure to the air, but if a
portion of yeast or nitrogenious organic matter of
any kind be added it soon acts as a. ferment, and
causes the spirit to unite with oxygen derived
from the atmosphere, and so to become sour from
the formation of acetic acid or vinegar. Acetic
acid is also produced on a large scale by heating
wood in a close vessel. A substance distills over,
which is acetic acid contaminated with empyreu-
matic and tarry matter; it is termed pyrolig-
neous acid, and is much used in commerce.
The most concentrated acetic acid may be
obtained by neutralizing common vinegar with
carbonate of soda, and crystallizing out the acetate
of soda so formed. This acetate of soda is then