Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/143

 F I B F I B 133 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 solu tion 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 fibre- yielding 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 fib rous substances of vegetable origin which have hitherto been employed for textiles and cordage, &c., to any con siderable extent. It is compiled from Dr H. Miiller s &quot; Pflanzenfaser&quot; in Hofmann s Bericht uberdie Entwickelung tier chemiscken Industrie, a paper to which we owe other obligations. The more closely vegetable fibres approximate to a con dition of absolute purity, the greater becomes the difficulty FIG. 1. Fibre of Sheep Wool (S. India). of distinguishing them from each other by any chemical tests. As, however, more or less incrusting substance ad heres to all bast fibres in their raw condition, they exhibit FIG. 2. Fibre of Wool of Cashmere Goat. 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 FIG. 3. Fibre of Alpaca Wool. 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 dis tinguished from other vegetable fibres which are composed of aggregated cells ; and still more marked is the difference FIG. 4. Bengal Silk Fibre. between vegetable fibres and wool and silk respectively. The accompanying woodcuts show the microscopic ap pearance 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 FIG. 5. Fibre of Sea-Island American Cotton. character, they can be readily recognized in any mixed fabric by appropiate tests. Thus aniline dyes, which com municate 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- FIG. 6. Cleaned Rhea Fibre. 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 uudissolved remains, the proportion of vegetable fibre may be ascertained. The FIG. 7. Fibre of Rough Russian Flax alkaline filtrate treated with acetate of lead gives a white precipitate for silk and black for wool. The sulphur con tained in w r ool, 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.) FIBRIN, or FIBRINE, is a member of the important group of albuminoid or proteinous substances which, embracing albumen, casein, gluten, and other allied compounds, con-