It will be of interest to mention now one or two of the uses of electric furnaces. The well-known substance calcium carbide, so much used for producing acetylene gas for lighting purposes, is a compound of calcium and carbon; it is made by raising a mixture of lime and coke to an intense heat in an electric furnace. The manufacture of calcium carbide is carried on on a very large scale at Niagara, with electric power obtained from the Falls, and at Odda in Norway, where the power is supplied by the river Tysse. Carborundum, a substance almost as hard as the diamond, is largely used for grinding and polishing purposes. It is manufactured by sending a strong current through a furnace containing a core of coke surrounded by a mixture of sand, sawdust, and carbon. The core becomes incandescent, and the heating is continued until the carbon combines with the sand, the process taking about a day. Graphite, a kind of carbon, occurs naturally in the form of plumbago, which is used for making black lead pencils. It is obtained by mining, but many of the mines are already worked out, and others will be exhausted before long. By means of the electric furnace, graphite can now be made artificially, by heating anthracite coal, and at Niagara a quantity running into thousands of tons is produced every year. Electric furnaces are now largely employed, particularly in France, in the production of the various alloys of iron which are used in making special kinds of steel; and they are used also to a considerable extent in the manufacture of quartz glass.