THE RARER METALS AND THEIR ALLOYS. 505 



He points out ' that Despretz 2 used in 1849 the heat produced 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 3,500° may be attained and that 

 many metallic oxides which until recently were supposed to be irre- 

 ducible may be readily made to yield the metal they contain. :i 



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 asso- 

 ciated 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, unfor- 

 tunately, the reductions are usually very tedious, and it would be 

 impossible to actually show you much if I were to attempt to reduce 

 before you any of the rarer metals; but as the main object is to show 

 you how the furnace is used, it may be well to boil some silver at a tem- 

 perature of some 2,500°, and subsequently to melt chromium in the 

 furnace (fig. 2, PI. XXIII). This furnace consists of a clay receptacle A 

 lined with magnesia B. A current of 60 amperes and 100 volts is intro- 

 duced by the carbon poles C, O 0'; an electro-magnet M is provided to 

 deflect the arc on to the metal to be melted. [By means of a lens and 

 mirror D E the image of the arc and of the molten metal was projected 

 onto a screen. For this purpose it was found convenient to make the 

 furnace much deeper than would ordinarily be the case.] 



The result is very beautiful, but can only be rendered in dull tones 

 by the accompanying illustrations (PI. XXIV). It may be well, there- 

 fore, to state briefly what is seen when the furnace is arranged for the 

 melting of metallic chromium. Directly the current is passed the pic- 

 ture reflected by the mirror E (fig. 2, PI. XXIII) shows the interior of 

 the furnace (fig. 1, PI. XXIV) as a dark crater, the dull red poles reveal- 

 ing the metallic luster and gray shadows of the metal beneath them. A 

 little later these poles become tipped with dazzling white, and in the 

 course of a few minutes the temperature rises to about 2,500° O. Such 

 a temperature will keep chromium well melted, though a thousand 



1 Ann. de Chim. et de Phys., Vol. IV, 1895, page 365. 



2 Comptes Rendus, Vol. XXVIII, page 755, and Vol. XXIX, 1849, pages 48, 545,712. 



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

 CXV, 1892, page 1031; ibid., Vol. CXVI, 1893, pages 347, 349, 549, 1222, 1225, 1429; 

 ibid., Vol. CXIX, 1894, pages, 15, 20, 935; ibid., Vol. CXX, 1895, page 290. The more 

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

 nium, molybdenum, tungsten, vanadium, and titanium. There is an important paper 

 by him on the various forms of the electric furnace in the Ann. de Chim. et de Phys,, 

 Vol, IV., 1895, page 365. 



