with rhodium), and graduated with the aid of the air thermometer, finally came into general use, and it proved to be quite reliable—but only up to 3,000° Fahr.,[1] which temperature was soon surpassed. Then, Le Chatelier devised a pyrometer based on the variations of intensity of light of fused metals at different temperatures, and this instrument again proved to be sufficiently accurate up to 3,600°; but this last temperature, too, is now surpassed by Moissan, by means of his new electric furnace, which is a real model of efficiency and simplicity.[2] It consists of two superposed bricks, made of quicklime, or of an especially pure calcinated magnesia. A groove with a small cavity in its middle (large enough to receive a small crucible) is made on the upper face of the lower brick in the sense of its length, and two carbon electrodes are introduced from both sides into the groove. As soon as they are connected with a dynamo machine the electric arc appears between their extremities, and an immensely high temperature is produced in the cavity. Thus, a small Edison machine, worked by a gas engine of eight horse power, gave a temperature estimated at" about 4,500° Fahr., and with a fiftyhorse-power engine the enormous temperature of about 5,400° (3,000° C.) was reached.
The effects of this little furnace are simply wonderful. At about 4,500° lime, strontia, and magnesia are crystallized in a few minutes. At 5,400° the very substance of the bricks is fused and flows like water. Oxides of various metals which were considered as quite irreducible are deprived of their oxygen in no time; nickel, cobalt, manganese, and chrome oxides can be reduced at a lecture experiment, and a piece of 120 grammes of pure uranium is obtained at once from the uranium oxide. At about 4,050° pure alumina is fused and little rubies are formed; true, they are less beautiful than those of Frémy, but the whole experiment lasts less than a quarter of an hour. At a higher temperature alumina is even volatilized, and nothing is left of it in the crucible. In short, the results are as interesting and as promising as those which Pictet and Dewar have witnessed when they went to the other end of the thermometric scale and produced the extremely low temperatures of about 200° C. below the freezing point.
And, finally, Moissan's discovery establishes a new link between the processes which we obtain in our laboratories and those which are going on in the celestial spaces, in the formation of meteorites. It was known long since that these masses of silicates and nickeled iron which travel in the interplanetary
