The Romance of Modern Chemistry

HIGH TEMPERATURES is of the utmost importance, as it turns out, for certain processes. It must be remembered too, that these objec- tions on the score of economy lose their force in cases where water-power is available for driving the dynamos, as it is, for example, at Niagara and in Norway. One of the chief difficulties in working at such high temperatures as are reached in the electric furnace is to find a suitably refractory substance out of which the enclosing box may be constructed. Up to a certain point quicklime is an excellent material. As its em- ployment in the oxy-hydrogen lime-light shows, it is not easily fused, and it has further the recommenda- tion of being a very poor conductor of heat. This latter property was well demonstrated in an experi- ment carried out by the French chemist Moissan, whose name will always be associated with the utilisation of the electric furnace. In one of the lime furnaces which he employed, the top consisted of a slab of quicklime rather less than inch thick. The electric arc was allowed to play for ten minutes in the cavity below the slab, the temperature rising probably to over 5000* Fahrenheit. In spite of this, the slab could be handled on the outside without discomfort, while examination of the lower surface, which had been in contact with the arc, showed that the quicklime had actually been melted over an area of several square inches. The tremendous heat, therefore, which had been generated in the cavity of the furnace had been completely kept in by a layer of lime 1| inch thick. With bigger currents and more powerful arcs even lime furnaces become useless; the lime fuses and runs like water, and ultimately it boils, producing clouds of smoke. The difficulty may be partly surmounted 198