The ferrotype and how to make it - The Grian Press

SILVER. 79
through the solution. Free iodide in the bath
is indicated by pin-holes in negatives, and by a
rough and sanded appearance of the plate when
removed from the bath, and by being covered
by black spots when developed.
The solution may also contain an excess of
organic matter, the presence of which is indicated
by a tendency to fog in the development, and by
an absence of transparency in the shadows, to
counteract which pure nitric acid is used. The
acid holds the organic matter in solution, but it
has also the evil effect of hastening the accumu-
lation of the cause of the first difficult}^, by
attacking the edges and unprotected portions of
the plates, and by taking up and holding in solution
s-uch particles of organic matter as may
collect in and upon the surface of the bath dish.
For this reason, the use ol nitric acid in the bath,
except in cases where it is absolutely necessary,
should be discountenanced.
We find, then, that our old solution is burdened
with a number of evil qualities, which we
will proceed to dispose of, and casting out, re-
store the solution to its pristine purity. For
tliat purpose, we will add to the solution sufficient
carbonate of soda or concentrated ammonia
to counteract the acid, barely enough to pre-
vent the change of color in litmus paper from
blue to red when immersed in the solution.
We will now pour into an evaporating, or other
dish, four fluid ounces of water, into which we