CELLULOSE.

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Mineral Thickenings.

Only two mineral thickenings are at present employed, namely, kaolin andpipe-clay ; these are generally used mechanically as resists. Pipe-clay andtorrefied starch are employed to print complicated patterns, especially inblock printing. The former is also used as a resist composition applied to partsof a fabric to prevent the deposition of colour or mordant upon those parts.By its use the quantity of gum required as a thickening is considerablyreduced. Steam colours thickened with pipe-clay lose from 35 to 50 per centof their intensity when applied to woollen tissues, but with cotton fabricslittle loss is experienced. Before its use pipe-clay should be carefully washedand deprived of all coarse particles by being made to pass through a fine sieve,and then allowed to deposit slowly from water; it should be free from oxideof iron. Kaolin is used in a similar manner, but is more expensive.

Vegetable Fibres. Vegetable Thickenings.

The most important vegetable fibres, cotton, flax, hemp, aloe fibre, NewZealand flax (the fibre of the Phormium tenax), jute (also called Bengalhemp), rame, woody fibre, and pine-apple fibre, are all composed chiefly ofcellulose mixed with different foreign substances, sometimes called colledtivelyjncrustating matter. Under this term is included colouring matter and apeculiar substance possessing organised strudture and known as suberine. Asthere exists a striking analogy between cellulose and vegetable thickenings, itis clear that an examination of the former leads diredtly to that of the latter.

Cellulose.

The study of the organs of plants teaches us that they are composed of anumber of cells and hollow vessels varying greatly in form and shape.These vessels are all filled either with air, essential oils, starch, or an endlessvariety of organic and inorganic substances, among which may he instancedsome peculiar adtive principles, sugar, fatty matter, and caoutchouc; but themain portion of plants, and the wood even of trees, consist of cellulose in astate more or less pure. This substance forms the connedling link between theanimal and vegetable kingdom, for it also constitutes the cutaneous envelopeand muscular system of the lowest form of animal life. As a type of perfectlypure cellulose we may take clean cotton fibre after it has been thoroughlybleached. In that state it is a colourless, inodorous, tasteless substance, in-soluble in and not adted upon by water, alcohol, ether, benzol, &c. Itssp. gr. is equal to i'525, water being i-ooo; and its chemical composition maybe expressed by the formula C6 Hi 0 0 5 or C 12 H 20 0 I0 ; it therefore belongs tothe carbo-hydrates, or substances in which hydrogen and oxygen are containedin the proportion in which they exist in water. Pure cellulose may beheated to 446° without alteration, but if subjedted to higher temperature itbecomes brown-coloured and decomposed. When submitted to destrudlivedistillation it yields water, carbonic acid, carburetted hydrogen, methylicalcohol, acetic acid, and creosote, with an abundant residue of porouscharcoal. It burns readily with proper access of air, emitting but little smoke,and no particular smell. When perfedtly pure or even nearly so, as in theform of well made paper, cellulose is quite indestrudtible by the adtion of