Fibres of animal origin are few, but of the highest value, while vegetable fibres are of endless variety, and of the most diverse character as to qualities and general utility. Animal fibres may be comprehended under two heads, silk and wool, using the terms in an extended sense. Silk of commerce is obtained from several species of moth or silkworm; and as wool there may be enumerated that produced by the numerous varieties of sheep, the mohair and cashmere wool obtained from varieties of goat, camels’ hair or wool, alpaca, and vicugna wool (see Alpaca, Woollen Manufactures, <fcc.). Several other animal fibres or hairs, and notably rabbit fur, are employed for felting, and the long fine hair of various animals has been occasionally woven into useful fabrics, without becoming recognized commercial staples. Animal fibres are closely related to each other in chemical composition, sharing their leading characteristics in common with all epidermic products, hair, horn, nails, feathers, &c. They belong to the nitrogenous or albuminoid group of substances, and are in composition intimately related to albumen, gelatin, and fibrin. They are insoluble in water or alcohol, but solutions of caustic alkalies cause them to swell up, and if boiled in these they dissolve with decomposition and the evolution of ammonia. Into the composition of wool sulphur enters, whereas the nitrogenous constituents of silk, which embrace albumen, gelatin, and a peculiar compound called fibroin, are free from that element. As is well known, these animal fibres yield a peculiar odour, like burning horn or feathers, on being ignited, and they carbonize with some difficulty only on the continued application of heat.

Chemically, vegetable fibres show a similar intimate relation to each other, the basis of all being cellulose, a compound allied in ultimate composition to the carbohydrates, starch and sugar, but possessing very marked and distinct ive characters. In particular, cellulose exhibits a remarkable indifference or resistance to the action of chemical reagents which affect allied substances and the bodies with which it is associated in growing plants. It is to this power of resisting change that its value for textile purposes is due, and on the same peculiarity is also based the ordinary method of separating fibres from other vegetable principles with which they are in general associated. Although cellulose is, however, practically unaffected by the ordinary solvents, water, alcohol, ether, benzol, and weak solutions of acids and alkalies even at high temperatures, yet under certain circumstances its physical qualities of strength and elasticity may be very seriously damaged without any appearance of chemical change. Strong solutions of acids and alkalies, especially if aided with heat, act upon cellulose by first swelling up the fibres; this is followed [table]

by their complete solution, and ultimately a change of chemical constitution takes place, the cellulose being transformed into glucose or grape sugar. Oxydizing agents again exercise a destructive influence upon cellulose, a fact of great importance in connexion with bleaching operations, which are all based upon the action of various oxidizing media. Cellulose is completely dissolved by ammoniacal solution of oxide of copper, and from its solution it may be precipitated chemically unchanged by treatment of the solution with acids.

The physical condition o. fibrous substances is, however, for textile purposes, of much more importance than their chemical purity. The length and strength of the fibre, its fineness and elasticity, and its colour are all considerations of the first importance. The period at which the fibreyielding plants are collected, and the various processes through which all the raw materials, with the exception of cotton and other seed hairs, pass to free the fibres, exercise important influences on the strength, elasticity, and original colour of the fibres. The almost invariable method by which vegetable fibres are freed from associated substances consists in retting or rotting, a process which will be fully described under Flax.

In the accompanying table are embraced all the fibrous substances of vegetable origin which have hitherto been employed for textiles and cordage, &c., to any considerable extent. It is compiled from Dr H. Müller’s “Pflanzenfaser” in Hofmann’s Bericht über die Entwickelung der chemischen Industrie,— a paper to which we owe other obligations.

The more closely vegetable fibres approximate to a condition of absolute purity, the greater becomes the difficulty of distinguishing them from each other by any chemical tests. As, however, more or less incrusting substance adheres to all bast fibres in their raw condition, they exhibit certain reactions by which, in that condition, they can be separately recognized, but such tests are of little practical value. More definite and important results can be obtained by microscopical examination, as certain peculiarities of minute structure are retained by fibres with great persistency. The microscopic distinction of allied fibres is, however, a difficult task, requiring much experience and discrimination. Cotton and other seed hairs, which consist of single elongated cells or tubes, are of course easily distinguished from other vegetable fibres which are composed of aggregated cells: and still more marked is the difference between vegetable fibrés and wool and silk respectively. The accompanying woodcuts show the microscopic appearance of wool, silk, cotton, rhea, and flax fibres, magnified in each case 320 diameters. As wool, silk, and vegetable fibres present marked differences of chemical character, they can be readily recognized in any mixed fabric by appropiate tests. Thus aniline dyes, which communicate strong permanent colours to wool and silk, only produce on vegetable fibres a fugitive, easily washed-out stain. Vegetable fibres in a mixed fabric may be distin guished by boiling a fragment of the material in a solution containing 10 per cent, of soda, whereby the animal fibres dissolve, leaving the vegetable fibres. By filtration and subsequent purifying of the undissolved remains, the proportion of vegetable fibre may be ascertained. The alkaline filtrate treated with acetate of lead gives a white precipitate for silk and black for wool. The sulphur contained in wool, from which silk is free, gives a ready means of distinguishing a mixture of these two fibres. In a solution of plumbate of soda wool becomes black, while silk is quite unaffected. (J. pa.)