Mechanical an Useful arts. On dyeing.

The Year-Book of Facts in Science and Art
Exhibiting the Most Important discoveries and Improvements of the past year,
in mechanics and the useful arts; natural philosophy; electricity; chemistry; zoology and biology; geology and geography; meteorology and astronomy.
By John Timbs,
editor of "the Arcana of Science and Art."
David Bogue, Fleet Street,
A Paper on this useful art has been read by Mr. Napier, to the Royal Institution. Having defined Dyeing to be the art of imparting colour to fibrous materials, Mr. Napier stated that he should confine his remarks to the processes of dyeing cotton. He noticed that, the fibres of raw cotton being enveloped in a resinous matter, it is necessary that it be boiled before it is subjected to the dye, an operation in which it loses from 7 to 9 per cent. of its weight. The principle of the use of mordants was then explained. There is, generally speaking, but little attraction between the colouring matter and the cotton. Hence the necessity for a mordant, i. e. an intermediate substance, which, being capable of uniting with the dye and the stuff, combines them permanently with each other. This remarkable property is possessed by the oxides of tin, lead, iron, and aluminum. Having exhibited the effects of mordants, and shown how by the expulsion of the acetic acid acetate of alumine was made to act as a mordant, Mr. Napier noticed that if nitrate of iron be exposed to sunlight, the colour produced is deepened by ferro-prussiate of potash. At the same time he admitted that, when an attempt was made to apply this principle to practical purposes, not half the usual intensity of colour was obtained. It was suggested as an explanation of this phenomenon, that the light either disables the iron from entering into the pores of the cotton, or else presents what Mr. Napier regards as a catalytic influence of the cotton itself. The well-known distinction between substantive and adjective colours having been illustrated, and safflower and indigo exhibited as types of the former, Mr. Napier showed how difficult it was in this, as in other branches of science, to lay down any rigid definition. Having mixed a mordant with an adjective, he produced effects which might fairly be ascribed to this mixture acting as a substantive colour — and he concluded by noticing the following process in dyeing silk. Safflower contains a red and also a yellow hue — the former injures the latter, and is soluble in water. Therefore the yellow tint having been washed out from it, the safflower is digested with carbonate of potass. This substance, however, though it dissolves the red tint, will not dye. The solution is therefore neutralized by an acid. When this is done, a mass of cotton placed in the middle of a vat filled with the dye absorbs the whole colouring matter. The cotton itself is next washed out in an alkali, the alkali again neutralized, and then the liquid is in a condition to dye silk.

Athenæum, No. 1063.

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