Mr Prentice says: "I may point out that while the ordinary process of making nitric acid is one of fractional distillation by time, mine is fractional distillation by space." "Instead of the operation being always at the same point of space, but differing by the successive points of time, I arrange for the differences to take place at different points of space, and these differences exist at one and the same points of time." It is possible with this plant to produce the full product of nitric acid of a gravity of 1.500, or to obtain the acid of varying strengths from the different still-heads. One of these stills, capable of producing about 4 tons of nitric acid per week, weighs less than 2 tons. It is claimed that there is by their use a saving of more than two-thirds in fuel, and four- fifths in condensing plant. Further particulars and illustrations will be found in Mr Prentice's paper (_Journal of the Society of Chemical Industry_, 1894, p. 323). CHAPTER III. _NITRO-CELLULOSE, &c._ Cellulose Properties--Discovery of Gun-Cotton--Properties of Gun-Cotton-- Varieties of Soluble and Insoluble Gun-Cottons--Manufacture of Gun-Cotton-- Dipping and Steeping--Whirling out the Acid--Washing--Boiling--Pulping-- Compressing--The Waltham Abbey Process--Le Bouchet Process--Granulation of Gun-Cotton--Collodion-Cotton--Manufacture--Acid Mixture used--Cotton used, &c.--Nitrated Gun-Cotton--Tonite--Dangers in Manufacture of Gun-Cotton-- Trench's Fire-Extinguishing Compound--Uses of Collodion-Cotton--Celluloid-- Manufacture, &c.--Nitro-Starch, Nitro-Jute, and Nitro-Mannite. ~The Nitro-Celluloses.~--The substance known as cellulose forms the groundwork of vegetable tissues. The cellulose of the woody parts of plants was at one time supposed to be a distinct body, and was called lignine, but they are now regarded as identical. The formula of cellulose is (C_{6}H_{10}O_{6})_{X}, and it is generally assumed that the molecular formula must be represented by a multiple of the empirical formula, C_{12}H_{20}O_{10} being often regarded as the minimum. The assumption is based on the existence of a penta-nitrate and the insoluble and colloidal nature of cellulose. Green (_Zeit. Farb. Text. Ind._, 1904, 3, 97) considers these reasons insufficient, and prefers to employ the single formula C_{6}H_{10}O_{5}. Cellulose can be extracted in the pure state, from young and tender portions of plants by first crushing them, to rupture the cells, and then extracting with dilute hydrochloric acid, water, alcohol, and ether in succession, until none of these solvents remove anything more. Fine paper or cotton wool yield very nearly pure cellulose by similar treatment.