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stearic acid, C18H36O2 and the acid C22H42O3. The cuto-celluloses have been only superficially investigated, and, with the exception of cork, are of but little direct industrial importance.

Industrial Uses of Cellulose.—The applications of cellulose to the necessities of human life, infinitely varied in kind as they are colossal in magnitude, depend upon two groups of qualities or properties, (1) structural, (2) chemical. The manufactures of vegetable textiles and of paper are based upon the fibrous forms of the naturally occurring celluloses, together with such structural qualities as are expressed in the terms strength, elasticity, specific gravity. As regards chemical properties, those which come into play are chiefly the negative quality of resistance to chemical change; this is obviously a primary factor of value in enabling fabrics to withstand wear and tear, contact with atmospheric oxygen and water, and such chemical treatments as laundrying; positive chemical properties are brought into play in the auxiliary processes of dyeing, printing, and the treatment and preparation in connexion with these. Staple textiles of this group are cotton, flax, hemp and jute; other fibres are used in rope-making and brush-making industries. These subjects are treated in special articles under their own headings and in the article Fibres. The course of industrial development in the 19th century has been one of enormous expansion in use and considerable refinement in methods of preparation and manufacture. Efforts to introduce new forms of cellulose have had little result. Rhea or ramie has been a favourite subject of investigation; the industry has been introduced into England, and doubtless its development is only a question of time, as on the continent of Europe the production of rhea yarns is well established, though it is still only a relatively small trade—probably two or three tons a day total production. The paper trade has required to seek new sources of cellulose, in consequence of the enormous expansion of the uses of paper. Important phases of development were: (1) in the period of 1860 to 1870, the introduction of esparto, which has risen to a consumption of 250,000 tons a year in the United Kingdom, at which figure it remains fairly steady; (2) the decade 1870 to 1880, which saw the development of the manufacture of cellulose from coniferous woods, and this industry now furnishes a staple of world-wide consumption, though the industry is necessarily localized in countries where the coniferous woods are available in large quantities. As a development of the paper industry we must mention the manufacture of paper textiles, based upon the production of pulp yarns. Paper pulps are worked into flat strips, which are then rolled into cylindrical form, and by a final twisting process a yarn is produced sufficiently strong to be employed in weaving.

What we may call the special cellulose industries depend upon specific chemical properties of cellulose, partly intrinsic, partly belonging to the derivatives such as the esters. Thus the cellulose nitrates are the bases of our modern high explosives, as well as those now used for military purposes. Their use has been steadily developed and perfected since the middle of the 19th century. The industries in celluloid, xylonite, &c., also depend upon the nitric esters of cellulose, and the plastic state which they assume when treated with solvent liquids, such as alcohol, amyl acetate, camphor and other auxiliaries, in which state they can be readily moulded and fashioned at will. They have taken an important place as structural materials both in useful and artistic applications. The acetates of cellulose have recently been perfected, and are used in coating fine wires for electrical purposes, especially in instrument-making; this use depends upon their electrical properties of high insulation and low inductive capacity. Hydrated forms of cellulose, which result from treatment with various reagents, are the bases of the following industries: vegetable parchment results from the action of sulphuric acid upon cellulose (cotton) in the form of paper, followed by that of water, which precipitates the partially colloidalized cellulose. This industry is carried out on “continuous” machinery, the cellulose, in the form of paper, being treated in rolls. Vulcanized fibre is produced by similar processes, as for instance by treating paper with zinc chloride solvents and cementing together a number of sheets when in the colloidal hydrated state; the goods are exhaustively washed to remove, last traces of soluble electrolytes; this is necessary, as the product is used for electrical insulation. The solvent action of cupro-ammonium is used in treating cellulose goods, cotton and paper, the action being allowed to proceed sufficiently to attack the constituent fibres and convert them into colloidal cupro-ammonium compounds, which are then dried, producing a characteristic green-coloured finish of colloidal cellulose and rendering the goods impervious to water. The important industry of mercerization has been mentioned above; this is carried out on both yarns and cloth of cotton goods chiefly composed of Egyptian cottons. A high lustrous finish is produced, giving the goods very much the appearance of silk.

Of special importance are the more recent developments in the production of artificial fibres of all dimensions, by spinning or drawing the solutions of cellulose or derivatives. Three such processes are in course of evolution, (1) The first is based on the nitrates of cellulose which are dissolved in ether-alcohol, and spun through fine glass jets into air or water, the unit threads being afterwards twisted together to constitute the thread used for weaving (process of Chardonnet and Lehner). These processes were developed in the period 1883 to 1897, at which later date they had assumed serious industrial proportions. (2) The cupro-ammonium solution of cellulose is similarly employed, the solution being spun or drawn into a strong acid bath which instantly regenerates cellulose hydrate in continuous length. (3) Still more recently the “viscose” solution of cellulose, i.e. of the cellulose xanthogenic acid, has been perfected for the production of artificial silk or lustra-cellulose; the alkaline solution of the cellulose derivative being drawn either into concentrated ammonium salt solutions or into acid baths. This product, known as artificial silk, prepared by the three competing processes, was in 1908 an established textile with a total production in Europe of about 5000 tons a year, a quantity which bids fair to be very largely increased by the advent of the viscose process, which will effect a very considerable lowering in the cost of production. The viscose solution of cellulose is also used for a number of industrial effects in connexion with paper-sizing, paper-coating, textile finishes, and the production of book cloth and leather cloth, and, solidified in solid masses, is used in preparing structural solids which can be moulded, turned and fashioned.

For the special literature of cellulose treated from the general point of view of this article, the reader may consult the following works by C. F. Cross and E. J. Bevan: Cellulose (1895, 2nd ed. 1903), Researches on Cellulose, i. (1901), Researches on Cellulose, ii. (1906).  (C. F. C.) 

CELSIUS, ANDERS (1701–1744), Swedish astronomer, was born at Upsala on the 27th of November 1701. He occupied the chair of astronomy in the university of his native town from 1730 to 1744, but travelled during 1732 and some subsequent years in Germany, Italy and France. At Nuremberg he published in 1733 a collection of 316 observations of the aurora borealis made by himself and others 1716–1732. In Paris he advocated the measurement of an arc of the meridian in Lapland, and took part, in 1736, in the expedition organized for the purpose by the French Academy. Six years later he described the centigrade thermometer in a paper read before the Swedish Academy of Sciences (see Thermometry). His death occurred at Upsala on the 25th of April 1744. He wrote: Nova Methodus distantiam solis a terra determinandi (1730); De observationibus pro figura telluris determinanda (1738); besides many less important works.

See W. Ostwald’s Klassiker der exacten Wissenschaften, No. 57 (Leipzig, 1904), where Celsius’s memoir on the thermometric scale is given in German with critical and biographical notes (p. 132); Marie, Histoire des sciences, viii. 30; Poggendorff’s Biog.-literarisches Handwörterbuch.

CELSUS (c. A.D. 178), a 2nd-century opponent of Christianity, known to us mainly through the reputation of his literary work, The True Word (or Account; ἀληθὴς λόγος), published by Origen in 248, seventy years after its composition. In that year, though the Church was under no direct threat of attack, owing