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ASBESTOS

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Originally appearing in Volume V02, Page 715 of the 1911 Encyclopedia Britannica.
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ASBESTOS , a fibrous See also:

mineral from Gr. aai(3earos, unquenchable, by transference, incombustible, in allusion to its See also:power of resisting the See also:action of See also:fire. The word was applied by Dioscorides and other See also:Greek authors to quicklime, but See also:Pliny evidently used it in its See also:modern sense. It was occasionally See also:woven by the ancients into handkerchiefs, and, it has been said, into shrouds which were used in See also:cremation to prevent the ashes of the See also:corpse from mingling with the See also:wood-ashes of the pyre. In different varieties of asbestos the See also:fibres vary greatly in See also:character. When silky and flexible they are sometimes known as See also:mountain See also:flax. The finer kinds are often termed See also:amianthus (q.v.). When the fibres are naturally interwoven, so as to forma felted See also:mass, the mineral passes under such trivial names as mountain See also:leather, mountain See also:cork, mountain See also:paper, &c. The asbestos formerly used in the arts was generally a fibrous See also:form of some See also:kind of See also:amphibole, like See also:tremolite, or anthophyllite, though occasionally perhaps a See also:pyroxene. In See also:recent years, however, most of the asbestos in the See also:market is a fibrous variety of See also:serpentine, known mineralogically as chrysotile, and probably some of the See also:ancient asbestos was of this character (see AMLAx-THUS). Both minerals possess similar properties, so far as resistance to See also:heat is concerned. The amphibole-asbestos, or See also:hornblende-asbestos, is usually See also:white or See also:grey in See also:colour, and may See also:present See also:great length of fibre, some of the See also:Italian asbestos reaching exceptionally a length of 5 or 6 ft., but it is often harsh and brittle. The serpentine-asbestos occurs in narrow See also:veins, yielding fibres of only 2 or 3 in. in length, but of great tensile strength: they are usually of a delicate silky lustre, very flexible and elastic, and of yellowish or greenish colour.

The See also:

Canadian asbestos, which of all kinds is at present the most important industrially, occurs in a small See also:belt of serpentine in the 'See also:province of See also:Quebec, principally near See also:Black See also:Lake and See also:Thetford, where it was first recognized as commercially valuable about 1877. The See also:rock is generally quarried, cobbed by See also:hand, dried if necessary, crushed in rock-breakers, and then passed between rollers; it is reduced to a finer See also:state of See also:division by so-called fiberizers, and graded on a shaking See also:screen, where the loosened fibres are sorted. The See also:process varies in different See also:mills. In the See also:United States asbestos is worked only to a very limited extent. An amphibole-asbestos is obtained from Sall Mountain, See also:Georgia; and asbestos has also been worked in the serpentine of See also:Vermont. It occurs also in See also:South Carolina, See also:Virginia, See also:Massachusetts, See also:Arizona and elsewhere. Dr G. P. See also:Merrill has shown that some asbestos results from a process of shearing in the rocks. Formerly asbestos was obtained almost exclusively from See also:Italy and See also:Corsica, and a large quantity is still yielded by Italian workings. This is mostly an amphibole. It is in some cases associated with nodules of See also:green See also:garnet known as " seeds "—Semenze dell' amianto.

Asbestos is widely distributed, but only in a few localities does it occur in sufficient abundance and purity to be worked commercially; it is found, for example, to a limited extent, at many localities in See also:

Tirol,' See also:Hungary and See also:Russia; See also:Queensland, New South See also:ales and New See also:Zealand. In the See also:British Isles it is not unknown, being found among the old rocks of See also:North See also:Wales and in parts of See also:Ireland. Byssolite or asbestoid is a See also:blue or green fibrous amphibole from Dauphiny. The Asbestos Mountains in Griqualand See also:West, Cape See also:Colony, yield a blue fibrous mineral which is worked under the name of Cape asbestos. This is referable to the variety of amphibole called See also:crocidolite (q.v.). It occurs in veins in slaty rocks, associated with jaspers and quartzites See also:rich in See also:magnetite and See also:brown See also:iron-ore. Their See also:geological position is in the Griqua See also:Town See also:series, belonging to what are known in South See also:Africa as the Pre-Cape rocks. Asbestos was formerly spun and woven into fabrics as a rare curiosity. See also:Charlemagne is said to have possessed a tablecloth of this material, which when soiled was purified by being thrown into the fire. At a See also:meeting of the Royal Society in 1676 a See also:merchant from See also:China exhibited a handkerchief of " See also:salamander's See also:wool," or linum asbesti. By the Eskimos of Labrador asbestos has been used as a See also:lamp-See also:wick, and it received a similar application in some of the sacred lamps of antiquity. In 'recent times asbestos has been applied to a great variety of uses in the See also:industrial arts, and its applications are constantly increasing.

Its economic value depends not only on its power of withstanding a high temperature, but also on its See also:

low thermal conductivity and its partial resistance to the attack of acids: hence it is used for jacketing boilers and See also:steam-pipes, and as a filtering See also:medium for corrosive liquids. It has also come into use as an electric insulator. It is made into See also:yarn, See also:felt, millboard, &c., and is largely employed as packing for See also:joints, glands and stopcocks in machinery. Fire-See also:proof sheathing and felt are used for flooring and roofing; fire-proof curtains have been made for the See also:stage, and even clothing for firemen. Asbestos enters into the See also:composition of fire-proof cements, plasters and paints: it is used for packing See also:safes; and is made into balls with fire-See also:clay for See also:gas-stoves. Various preparations of asbestos with other materials pass in See also:trade under such names as uralite, salamandrite, asbestolit h, gypsine, &c. "Asbestic"is the name given to a Canadian product formed by crushing the serpentine rock containing thin seams of asbestos, and mixing the result with See also:lime so as to form a See also:plaster.

End of Article: ASBESTOS

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