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CHAPTER XIII.
SILK.
OILK is valued on account of its high gloss, its fineness and great strength^^ and the beautiful colours it assumes in the dye-beck. It is the produceof an insedt, or rather the larva of an insetfi known as Bombyx or Phalcena mori.The insedt, and the tree upon the-leaves of which it feeds, are natives ofChina, where, according to the historical accounts, silk-worms have beenreared, and silk woven into tissues since the year 2698 b.c. From China thecultivation of the mulberry tree and the rearing of silk-worms became intro-duced into Persia and Hindostan; while sericiculture has been but morerecently known to Europeans. In France the mulberry tree and the wormwere first cultivated about 1494.
Silk, like the web of the spider, is a secreted substance, that is, it is ejedtedin a liquid state from the body of the insedt, and solidifies immediately oncontadt with the air. The spun fibre averages in length 350 metres; itsdiameter never exceeds -j £$ v ths of a millimetre. Viewed under the microscopeit has a somewhat flattened cylindrical appearance. Every fibre consists oftwo distindt parts, an external envelope and an interior textile fibre or truefibrome. The external layer consists of a mixture of albumenoid, nitrogenous,and fatty-resinous matters, to which is sometimes added a colouring matter.
With the exception of MM. Roard and G. J. Mulder, no scientific man hasattempted the investigation of the constitution of silk. M. Roard extradtedby means of alcohol from raw silk—(1) a wax-like substance similarto the cerotic acid, C27H54O2, of bees’-wax; (2) when raw yellow silkwas experimented upon, a colohring-matter incorporated with a brown-redresinous substance was found. According to M. Mulder, the latter canbe separated by repeatedly washing with an aqueous solution of causticpotash. White, as well as yellow, silk, when raw, yields upon treatmentwith boiling water a nitrogenous matter, which in its charadter andcomposition bears a close relation to gelatine, and, according to M. Mulder’sresearches, is identical therewith. When raw silk has been treatedconsecutively with water, alcohol, and ether, it yields on treatment withconcentrated and boiling acetic acid two different nitrogenised substances,one of which being soluble in the acid behaves with reagents similarlyto a solution of albumen in acetic acid, while its percentage com-position is that of albumen, although it differs in some respedts from thewhite of eggs. The other nitrogenised substance is insoluble, and consists ofpure fibro'ine. Silk therefore contains in raw state—(1) cerotic acid ; (2) a redcolouring-matter, not met with in white silk; (3) fatty substances; (4) resinousmatter; (5) a nitrogenised substance soluble.in boiling water or gelatine;(6) a nitrogenised substance insoluble in boiling water, but soluble in boilingconcentrated acetic acid ; (7) and finally, fibro'ine.