The Romance of Modern Chemistry

HIGH TEMPERATURES materials known to the chemist, it has at the same time brought to light a number of substances which are quite at home at these high temperatures; indeed it is the electric furnace alone which has enabled us to prepare them. Among these substances are the carbides—com- pounds of the metals with carbon—and it is in the pre- paration of one of these, namely, calcium carbide, that the electric furnace is most extensively employed at the present time. Moissan showed that by heating a mixture of pure lime and carbon in the electric furnace calcium carbide could readily be obtained, and this is the method now employed on the manufacturing scale, except that limestone and coke are used as crude materials instead of lime and carbon. The use of limestone instead of lime does not really involve any difference, for at the high temperature employed the limestone loses its carbon dioxide and is converted into lime. The other material, the coke, is at best a very impure form of carbon, so that the calcium carbide obtained in the manufacturing process is not a pure product. The essential chemical change which goes on in the electric furnace during the formation of carbide is an extremely simple one. Lime is a compound of two elements, calcium and oxygen, but this union is broken by the interposition of carbon at the high temperature of the furnace. This latter element combines with both the calcium and the oxygen, so that these two are sepa- rated. The new compounds formed, calcium carbide and carbon monoxide, are quite distinct in their properties, for the former remains in the furnace in a fused con- dition, while the latter is a gas, and escapes at once. As the reader probably knows, the characteristic feature of calcium carbide is that it gives off an inflammable 200