Page 156 - The Wellington photographic handbook

Ammonium Sulphocyanide (sulphocyanide of ammonia,
ammonium rhodanate).—This is usually sold in small wet-looking
crystals, which will keep fairly well in a bottle with a tight-fitting
stopper, but in any other case will rapidly absorb moisture from
the air, the result being a wet mass, which cannot be weighed
accurately. It is therefore easiest to at once dissolve the quantity
bought in cold water (it is very soluble), adding water until the
bulk of the solution is ten ounces for every ounce of the sulpho-
cyanide crystals dissolved. In the foregoing formulae ten minims
of this solution can then be substituted for each grain of the sulpho-
cyanide prescribed. This solution keeps well.
Citric Acid.—Sold both in powder and crystals. Either will
do. In the solid form citric acid keeps indefinitely, no special
precautions being required.
Copper Sulphate (otherwise blue vitriol or sulphate of copper).
—This salt should take the form of clean-looking deep blue crystals.
It should be bought, preferably, at the chemist's, as the quality
sold at oil shops is often very impure. It keeps perfectly in the
solid form. In solution it gradually goes cloudy in appearance,
but this does not interfere with its use. Hot water may be used
to dissolve it.
Ferric Ammonium Citrate.—Most chemists keep this salt
in the form of brown scales ; there is a green variety, which is said
to be better suited for photographic purposes, but the brown will
be found to answer all requirements. It is not likely to be impure.
It keeps very well, either in the dry state or in solution.
Gold Chloride (otherwise chloride of gold).—As this is an
expensive salt, it is good economy to buy only the best quality. It
is sold sealed up in glass tubes, each containing fifteen grains.
As only a grain or two is wanted at a time, and it is not convenient
to weigh out such small quantities, it is best kept in solution, in a
stoppered bottle. The tube, having previously been freed from any
adherent labels, is dropped into the bottle or measure, and broken
either by shaking or by striking with a glass rod. Fifteen drams
of distilled water are then added and the solution is ready. If
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