CELLULOSE (from cc/hi/a, dim. of cella, cell). The chief constitutent of the cell walls of all vegetable cells. These walls consti tute the plant-skeleton and also form a protective covering for the sensitive. living protoplasm. In certain plants the reserve food is stored up in the form of cellulose. The relative chemical composition of cellulose is shown by the formula, its molecular structure is, however. ex ceedingl• complex, probably much more so than that of starch, to which it is chemically allied. True cellulose is not found in animal tissues, though considerable amounts of it are digested and absorbed by man and especially by the herbi vora; its digestion is probably effected by a spe cific enzyme, of the action of which, however, nothing is at present positively known. The chief value of its digestion by the animal organ ism has been assumed to consist in this, that when it is dissolved. the true foodstuff of the cells is liberated and becomes available. Cellu lose is manufactured on a large scale from wood, cotton, linen raes, hemp, flax. and similar ma terials of vegetable origin. Being insoluble in all ordinary solvents. it may be readily separated from the other constituents, which are soluble in water. alcohol, ether, dilute alkali, or dilute acids. It is often further purified by treatment with a cold mixture of nitric acid and potassium chlorate (Schulze's reagent). The stability of cellulose is so great that considerable quantities of it are preserved unaltered through the process of formation of coal, in which its presence may he demonstrated by means of suitable reagents. It is soluble in an annnoniacal solution of cupric oxide. from which it separates out in a pure state on addition of acid; the precipitate is washed with alcohol. and the cellulose is thus obtained in the form of a white amorphous powder.
The action of sulphuric acid on cellulose de Fend. largely on the coneentration of the acid. .literately dilute sulphuric acid transforms it, in the cold, into 'colloidal cellulose,' which is soluble in water, but is reprecipitated on addi tion of a trace of acid or of salt solution. If cellulose is dissolved in strong sulphuric acid and the solution is diluted with water, a gelat separates out, which is known as only/oid. In the presence of acid, ainvloid
like starch, blue by a solution ut This transformation may be employed for de tecting the presence of cellulose. Vegetable parchment, too, is made from cellulose by the use of sulphuric acid: for this purpose unsized paper is immersed for a few instants into concentrated sulphuric acid and then immediately washed with water, the paper thus becoming more dura ble and less permeable to liquids. Another trans formation of cellulose, effected by sulphuric acid, may be mentioned here: if cellulose derived from cotton is digested for some time with strong sulphuric acid, then diluted with water and sub jected to pfldiniged boiling. the cellulose is partly converted into grape-sugar.
With strong nitric acid cellulose forms ex plosive nitrates known as iitri)-celliloses, the composition of which depends on the strength of the acid employed and the duration of the re action. Collodion is a solution mainly of the tetra-nitrate and the penta-nitrate of cellulose in a mixture of alcohol and ether. Guncotton is the hexa-nitrate of cellulose, obtained by the prolonged action of a mixture of concentrated nitric and sulphuric acids.
If distilled in retorts, out of contact with air, •cellulose is decomposed with formation of methyl alcohol, formic acid, acid, and various hydrocarbons. All of these products are formed also in the destructive distillation of wood.
Cellulose is employed, in one or the other form, for a variety of purposes in the arts. It is largely used ill the manufacture of paper and of explosives. By dissolving the nitrocelluloses of collodium in melted camphor the substance known as celluloid is obtained, and celluloid is now ex tensively employed for making various articles in common use. Praetical use is now also made of (lie swelling capacity of cellulose. The fact that the when wet, will rapidly fill up a hole that has been made through it, has sug gested the idea of employing it to prevent. leak through shot-holes. Within recent years the usefulness of cellulose for this purpose has been repeatedly denionst•attd, and at present the substance is actually employed as a packing for the sides of •ar-vessels. See CELL; CARBOHY DRATES.