SILK AND OTHER FIBRES.

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removed. Baume’s process leaves in the silk all the albumen; the gelatine,wax, and resinous matters only are dissolved, reducing considerably the per-centage of loss. It is stated that the Japanese and Chinese have practicalprocesses for bleaching silk without the use of soap or great loss in weight,but there is no definite information extant.

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Means of Distinguishing Silk and Other Fibres.

It is not at all difficult to distinguish wool from silk when attention is paidto the several solvents. There may be added to the information given underthe preceding heading the statement of the fact that pure quadrihydratednitric acid, while it dissolves silk, only colours wool yellow. Wool, owing tothe sulphur it contains T becomes coloured black in a solution of oxide of leadin caustic potash. Nitro-prusside of sodium is a more delicate reagent, thewool or silk having been dissolved in a caustic alkali. Silk and wool aredissolved in caustic alkalies when heat is applied ; cotton and linen fibresare not affected by similar treatment. Animal fibres emit on combustion thepeculiar odour of burnt feathers, become coloured yellow with nitric acid, andred with nitrate of mercury, and are not acted upon during steaming afterhaving been moistened with dilute mineral acids. Cotton, hemp, and flaxfibres burn without emitting the peculiar odour, and are strongly attackedduring steaming when previously moistened with even very dilute mineral acids.

The microscope, however, affords the most ready method of distinguishingfibres from each other. The fibre of cotton, Fig. 7, appears as a ribandtwisted spirally, and its characteristics are unmistakable. Flax fibre, Fig. 8,is neither stiff nor twisted, and is distinguished by the narrowness of itsinner tube. The fibre of silk, Fig. 10, is perfectly cylindrical throughout, nothollow inside, and the surface is smooth and glossy, whilst woollen fibres,Fig. g, are scaled and bark-like in appearance. Fig. n represents woollen,cotton, and silk fibres as they appear together under the object-glass of amicroscope magnifying 120 to 150 times. The sample of cloth to be sub-mitted to examination should be cut up, placed on a slide in water, and coveredwith a thin piece of glass. Other fibres may be distinguished readily by meansof the microscope; and for this purpose the following observations will befound of use:—

Manilla. —Fibrous bundles oval, nearly opaque, and surrounded by a con-siderable quantity of dried up cellular tissue, composed of rectangular cells.The bundles are smooth ; very few partly detached ultimate fibres are seen,and no spiral tissue.

Sizal. —Fibrous bundles oval and surrounded by cellular tissue. Smoothand very few ultimate fibres projecting from the bundles. More translucentthan Manilla, and always to be recognised by the large quantity of spiralfibres mixed up in the bundles.

New Zealand Flax, or Phormium Tenax .—In machine-dressed Phormiumthe bundles are translucent and irregularly covered with tissue. Spiralfibres can be detected amongst the bundles, but not in the same quantityas seen in Sizal. Many more ultimate fibres project from the bundles, whichare fiat instead of oval. In those places where the bundles are entirelyfreed from tissue they are generally divided longitudinally into two ortoore smaller bundles or fasciculi, and in these places the number of half-