_Amyloid._—When cotton is treated with 30 times its weight of sulphuric acid somewhat diluted (1 part H_{2}O, 4 parts H_{2}SO_{4}) it quickly dissolves, the solution being at first gelatinous, becoming afterwards syrupy. On pouring this solution into water, a white flocculent precipitate is formed, consisting of a substance closely resembling the cellulose from which it is derived, differing, indeed, only in being amorphous, and in being coloured blue by iodine. This substance, from its resemblance to starch, has been called _amyloid_. When sufficiently dehydrated it constitutes a swollen starchy mass, which dries to a brittle transparent solid. This transformation appears to consist in a simple hydration of the cellulose molecule, thus:— Cellulose. Amyloid. 2 (C_{6}H_{10}O_{5}) + H_{2}O = C_{12}H_{22}O_{11}. The modification of cellulose, which occurs on the conversion of unsized paper into the so-called parchment paper, by exposure for a short time to the action of strong sulphuric acid, and subsequent washing and drying, consists doubtless in a superficial conversion of the cellulose into _amyloid_, or a body closely resembling it. _Hydracellulose._—Closely related in composition to the above {13} described amyloid, is the substance called hydracellulose, into which cellulose is converted by exposure for some time to the action of moderately strong sulphuric, or hydrochloric acids (sp. gr. 1·35). This substance is also formed by the action of very weak acids, if the exposure of the cellulose be sufficiently prolonged. Its formation is accompanied by the complete disintegration of the cellulose. If the action of strong sulphuric acid be prolonged, a further modification ensues, dextrin or sugar being formed. These products have not been sufficiently studied to have established their exact identity with any of the substances known under these group-names. The dextrin has a close resemblance to the dextrin obtained from starch; the sugar is susceptible of fermentation; but beyond this nothing specific is known of these bodies. Their general properties, however, and mode of formation, sufficiently establish the fact that cellulose itself is constituted of similar molecules. The action of zinc chloride solution upon cellulose is similar to that of sulphuric acid. Cellulose in contact with iron, and in presence of air and moisture, is converted into a sugar and a gummy substance, which latter is converted into a sugar on boiling with dilute acids. Oxidised by potassium permanganate or bichromate in presence of acetic acid, it is converted into glucose, dextrin, and formic acid.