The wool dissolves,
and the indigo, being insoluble, remains, and can be recovered. Alkaline
carbonates and soap in solution have little or no injurious action if
not too strong, and if the temperature be not over 50 deg. C. (106 deg. F.).
Soap and carbonate of ammonium have the least injurious action. Every
washer or scourer of wool, when he uses soaps, should first ascertain if
they are free from excess of alkali, _i.e._ that they contain no free
alkali; and when he uses soda ash (sodium carbonate), that it contains
no caustic alkali. Lime, in water or otherwise, acts injuriously,
rendering the fibre brittle.
_Reactions and tests proving chemical differences and illustrating modes
of discriminating and separating vegetable fibres, silk and wool, fur,
etc._--You will remember I stated that the vegetable fibre differs
chemically from those of silk, and silk from wool, fur, and hair, in
that with the first we have as constituents only carbon, hydrogen, and
oxygen; in silk we have carbon, hydrogen, oxygen, and nitrogen; whilst
in wool, fur, and hair we have carbon, hydrogen, oxygen, nitrogen, and
sulphur.
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