1895.] on the Barer Metals and their Alloys. 505 



property of burning in nitrogen — it presents } in fact, the only known 

 instance of vivid combustion in nitrogen.* 



Titanium may be readily reduced from its oxide by the aid of 

 aluminium. Here are considerable masses, sufficiently pure for 

 many purposes, which I have recently prepared in view of this 

 lecture. 



The other method by which the rarer metals may be isolated is 

 that which involves the use of the electrical furnace. In this con- 

 nection the name of Sir W. Siemens should not be forgotten. He 

 described the use of the electric arc furnace in which the carbons 

 were arranged vertically, the lower carbon being replaced by a 

 carbon crucible ; and in 1882 he melted in such a furnace no less 

 than ten pounds of platinum during an experiment at which I had 

 the good fortune to assist. It may fairly be claimed that the large 

 furnaces with a vertical carbon in which the bath is maintained fluid 

 by means of the electric current, the aluminium and other metals being 

 reduced by electrolytic action, are the direct outcome of the work 

 of Siemens. 



In the development of the use of the electric arc for the isolation 

 of the rare, difficultly fusible metals Moissan stands in the front 

 rank. He points out f that Despretz } used in 1849 the heat pro- 

 duced by the arc of a powerful pile ; but Moissan was the first to 

 employ the arc in such a way as to separate its heating effect from 

 the electrolytic action it exerts. This he does by placing the poles 

 in a horizontal position, and by reflecting their heat into a receptacle 

 below them. He has shown, in a series of classical researches, that 

 employing 800 amperes and 110 volts a temperature of at least 

 3500° may be attained, and that many metallic oxides which until 

 recently were supposed to be irreducible may be readily made to 

 yield the metal they contain. § 



A support or base for the metal to be reduced is needed, and this 

 is afforded by magnesia, which appears to be absolutely stable at the 

 utmost temperatures of the arc. An atmosphere of hydrogen may be 

 employed to avoid oxidation of the reduced metal, which, if it is not 

 a volatile one, remains at the bottom of the crucible almost always 

 associated with carbon — forming, in fact, a carbide of the metal. I 

 want to show you the way in which the electric furnace is used, but, 



* Lord Rayleigh has since stated that titanium does not combine with argon ; 

 and M. Guntz points out that lithium in combining with nitrogen produces 

 incandescence. M. Moissan has also shown that uranium does not absorb argon. 



t Ann. de Chim. et de Phys. vol. iv. 1895, p. 365. 



X Comptes Rendus, vol. xxviii. p. 755, and vol. xxix. 1849, pp. 48, 545, 712. 



§ The principal memoirs of M. Moissan will be found in the Comptes Rendus, 

 vol. cxv. 1892, p. 1031 ; ibid. vol. cxvi. 1893, pp. 347, 349, 549, 1222, 1225, 1429 ; 

 ibid. vol. cxix. 1894, pp. 15, 20, 935; ibid. vol. cxx. 1895, p. 290. The more 

 important of the metals he has isolated are uranium, chromium, manganese, 

 zirconium, molybdenum, tungsten, vanadium and titanium. There is an impor- 

 tant paper by him on the various forms of the electric furnace in the Ann. de 

 Chim. et de Phys., vol. iv. 1895, p. 365. 



