Page 158 - The Wellington photographic handbook

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Nitric Acid (otherwise known as aqua fortis).—This should
be a colourless fuming liquid. It is but little used in photography.
Being very corrosive it should be kept in a stoppered bottle. The
ordinary quality answers every photographic purpose.
Potassium Bichromate (also called red chromate of potash
and potassium dichromate).—This is sold in the form of fine
orange-red crystals. It keeps well both in the solid form and in
solution.
Potassium Bromide (otherwise bromide of potash).—This
should either be in the form of a coarse white powder, or crystals
mostly cubical. It is very soluble, keeps well in the solid or in
solution, and is not likely to be met with in an impure state.
Potassium Carbonate (also called carbonate of potash).
This is a coarse white powder, which must be kept in a well-corked
bottle, or it will absorb moisture from the air, cake hard and
finally turn liquid. In solution it keeps well, but its solutions
should not be put in stoppered bottles, as it makes the stoppers
stick. It is best to get " photographic " quality, as some of the
commercial carbonate is very impure.
Potassium Citrate (otherwise neutral potassium citrate or
citrate of potash).—This is a granular white powder, which is very
soluble in water. It is not likely to be met with in an impure
condition.
Potassium Ferricyanide (ferricyanide of potash, red prussiate
of potash).—This salt is sold in ruby red crystals, which should
be clean and bright and free from any orange-coloured powder
or dust. It must not be confused with potassium ferrocyanide,
yellow prussiate of potash, a salt which occurs in large lemon
yellow crystals and is seldom used in photography. The ferri-
cyanide keeps very well in solid form, fairly well in solution, but
this depends largely on the purity of the water used to dissolve it.
The best quality of ferricyanide should be obtained, as some of the
commercial samples are anything but pure.
Potassium Hydrate (otherwise called caustic potash).
This is sold in white, hard sticks, which must be kept well corked
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