The Romance of Modern Chemistry

SMALL CAUSES; GREAT EFFECTS and is obtained chiefly from monazite sand, found in Brazil and in the United States. The remaining 1 per cent, of the mantle is ceria, the oxide of the rare metal cerium, and, in spite of its small proportion, it is on this admixture that the virtue of the mantle wholly depends. Mantles composed of pure thoria alone would be of no use, for when put in a Bunsen flame they give out only a dull light. On the other hand, if more than 1 per cent, of ceria is added to the thoria a less brilliant effect is obtained; it is, in fact, possible to have too much of a good thing. Not only has this paltry 1 per cent, of ceria made the incandescent mantle a brilliant success; it has indirectly been the salvation of the gas industry. In competition with electricity, gas would have been badly beaten as a source of light had it not been for the discovery of the incandescent mantle. By its agency the illuminating power of a cubic foot of coal gas is enormously increased. Another interesting fact in connection with the in- candescent mantle deserving of passing notice is the extraordinary effect which the rapidly increasing use of thorium nitrate had on the price of that article. Early in 1894, an ounce of thorium nitrate sold for 55s.; by January 1895, on account of competition and improved methods of production, the price had fallen to 25s., by July 1895 to 14s., by November of the same year to 8s. In another six months the price was again halved, while at the present time it has fallen to about Is. Seldom indeed has any chemical product undergone such a rapid change in price. Another interesting illustration of the extraordinary influence exerted by small quantities of foreign matter is furnished by the behaviour of certain phosphorescent substances. Among them are the sulphides of the metals 329