About two grms. are taken and dried at 110–115° C. until the weight remains constant: the loss represents water. The fibre is then treated with a hot mixture of benzene and alcohol, dried as before and weighed: the loss is fat, wax, {45} &c. The residue from this treatment is then repeatedly exhausted with boiling water and again dried at 110–115° C. and weighed: the loss is put down as aqueous extract. The exhausted fibre is then treated for cellulose by either of the methods given on p. 19. The ash is determined in a separate portion. {46} CHAPTER IV. AN ACCOUNT OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF THE PRINCIPAL RAW MATERIALS. This chapter contains the results obtained from an investigation of the different plant fibres by the methods indicated in the two previous chapters. In the following table the fibres are classified according to the reactions which they give with iodine solution. CLASSIFICATION OF PLANT FIBRES ACCORDING TO THEIR COLOUR REACTION WITH IODINE SOLUTION (VÉTILLART). A. B. C. Seed Hairs. Dicotyledonous Monocotyledonous Bast Fibres. Fibres corresponding to Bast Fibres. Blue reaction Cotton. Linen. Straw. Hemp. Esparto. China grass. Pine apple. Paper mulberry Sunn. Yellow reaction Jute. New Zealand flax. Yucca. Hibiscus. Aloe. Manilla hemp. Class A. COTTON.—Genus, _Gossypium_. Order, _Malvaceæ_. Seed hairs, consisting of ultimate fibres. Length, 2·0–4·0 c.m., diameter, 0·012–0·037 mm. Mean ratio, 1250. Illustrated in Fig. 5: _a_, sections; _b_, longitudinal views; _c_, ends; mag. 300. Microscopic features.—Fibres simple, opaque, flattened, always more or less twisted upon itself, side wall membranous, showing striæ. {47} Sections.—Simple, oval, irregular, central cavity often containing granules. Micro-chemical reaction.—Blue with iodine solution. [Illustration: FIG. 5.] General chemical characteristic.—Pure cellulose basis with slight admixture of colouring matters, &c. COMPOSITION OF RAW FIBRE. Church. Müller. Cellulose 91·15 91·35 Fat 0·51 0·40 Aqueous extract (containing nitrogeneous substances) 0·67 0·50 Water 7·56 7·00 Ash 0·11 0·12 Cuticular substance (by difference) .. 0·63