Page 161 - The Wellington photographic handbook

is one of the most important chemicals the photographer uses.
It should be, when bought, in clean waxy-looking crystals, with
no white powder on them or loose in the bottle. If there is much
of this white powder the sulphite has been badly kept. It must
be kept in a well-corked bottle, as in the air it rapidly spoils, passing
to a white powder, which is quite useless photographically. Sulphite
soon dissolves in cold water, and still more readily in warm water.
When very hot water is poured on crystals of sulphite, they go a
quite opaque white before dissolving, but this change is not harmful.
If a bottle of sulphite is opened, a little taken out, and the rest
is not likely to be required for some time, it is well to melt the end
of a candle over the top of the bottle to seal it up. It then keeps
very well. If the sulphite crystals have a coating of white powder
on them, but are clean and bright underneath, a little extra may
be allowed in weighing out, the crystals given a rinse in cold
water for a moment to remove the powder, this water thrown
away, and the washed crystals dissolved in the usual way. This
should always be done when making up an amidol developer if the
sulphite is not quite clean. There is also on the market " anhydrous
sodium sulphite." This is a fine, white powder and weight for
weight is twice as strong as the crystals. The formula; in this
book are all for crystallized sulphite. If the anhydrous sulphite
is to be used, one-half as much as is stated will be correct. Stock
solutions of sulphite must not be kept.
Sulphuric Acid.—This is an almost water-white liquid,
extremely corrosive and caustic, and should be handled with great
care, as it will " burn " anything it touches. When mixed with
water great heat is generated. The acid should always be added
slowly to water, not water to acid.
Thiocarbamide.—This is a white powder not likely to be
met with in an impure state.

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