Page 155 - The Wellington photographic handbook

Alum.—There are many forms of alum known to chemists,
but the word " alum " by itself means potash alum. It is sold in
crystals or in powder form. There is no need for photographic
alum to be specially pure, the ordinary quality does quite well.
Alum dissolves much more easily in hot than in cold water.
Chrome Alum is a deep purple crystalline salt. Its solution
is purple by reflected and reddish by transmitted light. It exercises
a more intense hardening action than potash alum.
Amidol (or Diamidophenol, to give it its correct chemical
name).—This is generally in the form of a fine grey powder,
which dissolves readily in water or in a solution of sodium
sulphite. Amidol keeps fairly well in powder form, but in solution
for a few days only. With age amidol becomes darker in
appearance, but some samples are normally much darker than
others. The amidol powder should always be kept in a well
corked or stoppered bottle.
Ammonia (also called liq. amm. fort., or -880 Ammonia, the
•880 referring to its specific gravity).—This should be a clear water
white liquid, with an intense ammoniacal smell. It is so strong
that it is dangerous to smell at a bottle of ammonia, and if the eyes
are brought near an open bottle, they suffer severely. It should
be kept in a stoppered bottle, and, except that every time the
bottle is opened the liquid gets a little weaker, it keeps indefinitely.
Ammonium Bromide (otherwise known as bromide of ammonia).
—This should be a coarse white powder, which dissolves very easily
in cold water. It is not likely to be met with in an impure form
and keeps very well both solid and in solution. The bottle in
which the powder is kept should be well corked.
Ammonium Carbonate (also known as carbonate of ammonia
and lump ammonia).—This should be in the form of tough waxy
looking white lumps, with not more than a slight coating of white
powder on the outside. A little extra should be allowed when
weighing out and the white powder rinsed off. Ammonium car-
bonate does not keep very well, either solid or in solution, and
neither should be used if kept more than three months. The
quality stocked by most druggists is pure enough for photography.

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