If we write on paper with dilute sulphuric acid, and dry
and then heat the place written upon, the cellulose is destroyed and
charred, and we get black writing produced. The principle involved is
the same as in the separation of cotton from mixed woollen and cotton
goods by means of sulphuric acid or vitriol. The fabric containing
cotton, or let us say cellulose particles, is treated with dilute
vitriol, pressed or squeezed, and then roughly dried. That cellulose
then becomes mere dust, and is simply beaten out of the intact woollen
texture. The cellulose is, in a pure state, a white powder, of specific
gravity 1.5, _i.e._ one and a half times as heavy as water, and is quite
insoluble in such solvents as water, alcohol, ether; but it does
dissolve in a solution of hydrated oxide of copper in ammonia. On adding
acids to the cupric-ammonium solution, the cellulose is reprecipitated
in the form of a gelatinous mass. Cotton and linen are scarcely
dissolved at all by a solution of basic zinc chloride.
[Footnote 1: _J.
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