626 THE POPULAR SCIENCE MONTHLY. 



with rhodium), and graduated with the aid of the air ther- 

 mometer, finally came into general use, and it proved to be quite 

 reliable but only up to 3,000 Fahr.,* 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 sur- 

 passed by Moissan, by means of his new electric furnace, which 

 is a real model of efficiency and simplicity.! 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 fifty- 

 horse-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 Fre'my, 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 be- 

 tween 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 



* C. Barus in Philosophical Magazine, fifth series, xxxiv, 376 ; L. Holborn and W. Wien 

 n Wiedemann's Annalen, xlvii, 10Y. 



f Comptes Rendus, December 12, 1892, tome cxv. 



