146                           PRECIOUS STONES.
	of Brazilian Ruby—is a distinct Gem, seldom chosen for jewelry, hut useful for optical purposes. Of the several varieties, the only one occasionally employed is that of a dark, olive-green tint. It is discovered also red, and pink, as " rubeolite " ; blue, as indiolite ; white, brown, and black. The red Tourmaline is that found in Ceylon, and in Siberia, which is known in commerce as the " Brazilian Ruby " ; for which stone it is sometimes sold in mistake. The green, and blue varieties of Tourmaline are got from the Brazils, being occasionally called the Brazilian Emerald, and Sapphire. Chemically each of the Tourmalines contains silica, alumina, magnesia, oxide of iron, boracic acid, some soda, and some fluorine. By taking into consideration the physical, and the drug actions of these chemical elements, on the body, and mind, when administered therapeutically, we may form some conclusions about such influences for good, or evil, as the stones now under notice are likely to exercise on sensitive subjects, when worn as jewels, or otherwise externally applied. The said drug actions have already been considered here, of these several constituents ; except as regards Magnesia, Fluorine, Boracic acid, Potash, and Soda. Magnesia is the basic oxide of magnesium, which mineral, in one form or another, is universally dissemin­ated throughout the whole of the earth's crust. Traces of it are, moreover, to be found in the ashes of all plants, and it is present furthermore in almost all Natural Waters. As familiar medicaments, carbonate of magnesia, and siilphate of magnesia (Epsom Salts), are well known to everyone. The chloride of magnesium corresponds pretty closely with chloride of sodium (common salt), and it has been authoritatively supposed