Chemical changes at high temperatures have long been an object of research, but it was not until the introduction of the electric furnace that it was possible to command temperatures high enough to make exhaustive studies. In the last few years several chemists, especially Moissan, of Paris, and his pupils, have done systematic work with the aid of the arc furnace. The furnace used in the laboratory for high temperature work is a small and simple apparatus; Moissan’s furnace is a block of quick lime a little longer and wider than a page of this magazine and about three inches thick. A rectangular cavity is cut on the upper surface of this block. A similar block forms the cover. In opposite grooves between the top and bottom piece are placed the carbons, such as are used in ordinary arc lights. The arc plays across the cavity in such a manner that the substance to be heated is not brought into the arc itself, which is vaporized carbon, but below it. The cavity thus represents a tiny reverberatory furnace; the arc heats the roof and sides to an intense heat, which is radiated on the open dish or closed crucible or tube containing the substance heated. This is the simplest form of laboratory furnace. Various modifications are used, but in all the size is small and the arrangement simple. A powerful arc plays in the smallest possible cavity with the object of attaining the maximum of temperature, expense and duration of material being secondary considerations. Lime and magnesia are the best materials, because they are at the same time the most refractory substances available and are poor conductors of heat. A furnace top one and one half inches thick may be heated by so powerful an arc that the melted quick lime drips from the inner surface, while the outer surface is scarcely warm to the touch of the hand. Moissan has utilized in these little furnaces currents of electricity of varied strength, the lowest being that given by a four horse-power dynamo, the highest that generated by three hundred horse power. The highest temperatures obtained were about 3,500° centigrade (6,300° Fahrenheit), with the heat constantly increasing; the limit to the obtainable temperature--as far as the experimental evidence showed--was merely the lack of any known substance refractory enough to bear the heat; for at the temperature mentioned quick lime and magnesia not only melt but are changed into gases, so that the furnace was filled with the vapors of its own material.