About four pounds of benzoin B of best quality is broken into small pieces and placed in a small copper boiler K (Fig. 3); over its entire surface is pasted white blotting paper L, and to this is pasted a cone of strong paper which must surround the edge of the boiler. The cone ends above in a paper tube R, about five feet long and an inch wide. The copper boiler is placed in a large clay pot T (a flower pot) and surrounded on all sides with fine sand. The clay pot is heated from without by a charcoal fire. After the pot has remained about half an hour on the fire, the latter is fanned to its utmost and kept at this point for thirty minutes. The heat volatilizes the benzoic acid, the above-mentioned essential oil, and some tarry substances of a brown color. The latter are arrested by the filter paper, while the benzoic acid is deposited on the cone and in the tube, in the form of delicate glossy needles which are very fragrant owing to the essential oil. The largest yield of benzoic acid is obtained when the temperature is raised very gradually, until finally nothing remains in the copper boiler but a brown, almost carbonized mass of a blistered appearance. [Illustration: FIG. 3.] BORAX (SODII BORAS) is used in some preparations. Borax forms colorless crystals which slightly effloresce in dry air and hence must be preserved in tightly closed vessels. Reddish tinted crystals are contaminated with oxide of iron and should be rejected. PERMANGANATE OF POTASSIUM (POTASSI PERMANGANAS) is a salt formed by fusing a mixture of manganese dioxide, potassa, and potassium chlorate, extracting the product with water, and evaporating the solution to crystallization; the salt is obtained in small dark violet, almost black crystals which dissolve in sixteen parts of water to which they impart a beautiful violet color. By contact with organic substances, or others easily oxidized, the solution changes its color into green and finally is decolorized, precipitating a brown powder. Owing to this change of color the salt has been called chameleon mineral. As its preparation requires considerable dexterity, it is preferable to buy it from reputable houses, rather than to make it. It is used in the manufacture of mouth washes and hair dyes. The solution of the salt causes brown stains on linen and the skin; they can be removed only if the spots are immediately washed with hydrochloric, oxalic, sulphuric, or another acid. ACETIC ACID (ACIDUM ACETICUM).