_Terebene_, a mixture of dipentene and other hydrocarbons prepared from turpentine oil by treatment with concentrated sulphuric acid, is used chiefly in medicated soaps. Its specific gravity at 15 deg. C. is 0.862-0.868; the oil is frequently slightly dextro- or laevo-rotatory; the refractive index at 20 deg. C., 1.470-1.478. _Terpineol_, an alcohol also prepared from turpentine oil by the action of sulphuric acid, terpene hydrate being formed as an intermediate substance. It has a distinctly characteristic lilac odour, and on account of its cheapness is much used in soap perfumery, especially for a lilac or lily soap. Its specific gravity at 15 deg. C. is 0.936-0.940; refractive index at 20 deg. C., 1.4812-1.4835; and boiling point about 210 deg.-212 deg. C. It is optically inactive, and readily soluble in 1.5 volumes of 70 per cent. alcohol. _Vanillin_, a white crystalline solid, melting at 80 deg.-82 deg. C. and prepared by the oxidation of isoeugenol. It has a strong characteristic odour, and occurs, associated with traces of benzoic acid and heliotropin, in the vanilla bean. It can only be used in small quantity in light-coloured soaps, as it quickly tends to darken the colour of the soap. CHAPTER IX. GLYCERINE MANUFACTURE AND PURIFICATION. _Treatment of Lyes--Evaporation to Crude Glycerine--Distillation--Distilled and Dynamite Glycerine--Chemically Pure Glycerine--Animal Charcoal for Decolorisation--Glycerine obtained by other Methods of Saponification--Yield of Glycerine from Fats and Oils._ As pointed out in Chapter II. the fatty acids, which, combined with soda or potash, form soap, occur in nature almost invariably in the form of glycerides, _i.e._, compounds of fatty acids with glycerol, and as the result of saponification of a fat or oil glycerine is set free. In Chapter V. processes of soap-making are described in which (1) the glycerine is retained in the finished soap, and (2) the glycerine is contained in the lyes, in very dilute solution, contaminated with salt and other impurities. These lyes, though now constituting the chief source of profit in the manufacture of cheap soaps, were till early in last century simply run down the drains as waste liquor. Much attention has been devoted to the purification and concentration of glycerine lyes; and elaborate plant of various forms has been devised for the purpose.