05 (10 deg. Twaddell) is added. On boiling, the wool and silk dissolve,
whilst the cellulose fibre, cotton, remains undestroyed.
IV. If, instead of caustic soda as in III., a solution of oxide of
copper in ammonia be used, cotton and silk are dissolved, but wool
remains unchanged, _i.e._ undissolved. If sugar or gum solutions be
added to the solutions of cotton and silk, the cotton cellulose is
precipitated, whilst the silk is not, but remains in solution.
V. Another alkaline solvent for silk, which, however, leaves undissolved
cotton and wool, is prepared as follows: 16 grains of copper sulphate
("blue vitriol," "bluestone") are dissolved in 150 c.c. of water, and
then 16 grains of glycerin are added. To this mixture a solution of
caustic soda is added until the precipitate first formed is just
re-dissolved, so as not to leave an excess of caustic soda present.
LECTURE III
WATER: ITS CHEMISTRY AND PROPERTIES; IMPURITIES AND THEIR ACTION; TESTS
OF PURITY
I have already had occasion to refer, in my last Lecture, to water as a
chemical substance, as a compound containing and consisting of hydrogen
and oxygen.
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