The greater portion of the substances to be here described it will hardly be the province of the perfumer to prepare himself, as they are furnished by chemical factories at low prices; but some of them—for instance, sublimed, natural benzoic acid suitable for perfumery and a few other substances—the perfumer should make himself, in order to be sure of its genuineness. Therefore, while in the former class it will be sufficient to describe their properties to enable the manufacturer to distinguish good quality from bad, the latter class must be discussed at greater length. A. Chemicals used for the Extraction of Aromatic Substances. For the extraction of aromatic substances from plants a number of bodies are used which possess great solvent power for essential oils, and are besides very volatile, or have a low boiling-point. These are particularly ether, chloroform, petroleum ether, and bisulphide of carbon. ETHER. This liquid, in commerce also called sulphuric ether, is made in large quantities in chemical laboratories by the distillation of alcohol with sulphuric acid, followed by a second distillation or rectification. When pure, ether forms a mobile, thin, strong-smelling, and inflammable liquid which when inhaled produces insensibility, for which reason it is used as an anæsthetic in surgery. Its specific gravity is about 0.720 when anhydrous, and its boiling-point 35° C. (95° F.). It forms an excellent solvent for essential oils, resins, fats, and similar bodies. Owing to its great volatility, its vapors are quickly diffused in the air, and, as they are very inflammable, lights must be kept away from a bottle containing this substance. The same remark applies to most of the substances to be presently described. CHLOROFORM is prepared by the distillation of chlorinated lime, alcohol, and water, acetone being more recently substituted for the alcohol, followed by rectification of the product. When inhaled it produces insensibility like ether. It has a pleasant odor and sweet taste. Its specific gravity is about 1.49 and its boiling-point 61° C. (142° F.). Owing to its great solvent power and low boiling-point, chloroform is largely used for the extraction of aromatic vegetable substances; it does not take fire directly in the air. PETROLEUM ETHER.