FURNACE REACTIONS UNDER HIGH GASEOUS PRESSURES. 449 



By referring again to Table VIII. it will be found that this view is substantiated 

 by a comparison between the arc and resistance experiments. 



In the latter the yield is always extremely low. This may be explained by the 

 fact that as the inner layer of mixture approaches its fusing point it flows away by 

 gravity, and, ceasing to transmit the current, is not maintained at the requisite 

 temperature for marked reduction to occur. 



We come now to that curious apparent contradiction of facts which has for so long 

 puzzled investigators in this field ; namely, that though aluminium bronze and ferro- 

 aluminium can be so readily produced, no process exists by which the metal itself can 

 be obtained from the oxide, except by indirect means. What is, then, the function of 

 the auxiliary metal ? It has been suggested that a marked chemical affinity exists 

 between the aluminium and the metal with which it alloys, the evidence in support 

 of this being the high heat evolution which is noticeable when aluminium is added to 

 the metals in a molten state. 



It must, however, be remembered that under ordinary conditions the fused metals 

 contain dissolved oxide, and it therefore seemed worth while to carry out a preliminary 

 investigation of this question. 



Upon adding aluminium to molten copper in a thoroughly reduced condition, there 

 is no visible evidence of a reaction, and such pyrometric measurements as were made 

 sufficed to show that no considerable amount of heat could have been evolved. 



Thus we feel justified in concluding that the copper or other metal serves chiefly 

 to condense and dissolve the aluminium, and does not itself take part in the primary 

 chemical reduction of the oxide. 



A secondary function of the auxiliary metal is, however, possible. It occurred to 

 us that the absence of aluminium carbide, when reduction is effected in the presence 

 of other metals, might be explained by some chemical action of the aluminium carbide 

 upon the copper or iron or one of their oxides. 



An investigation of this matter has been undertaken by J. N. PRING,* whose 

 results clearly show that at the temperatures we are considering, namely, at or above 

 the melting-point of alumina, aluminium carbide reacts with either the oxide or the 

 metal, forming an alloy. 



The third problem, viz,, the limitation of the formation of carbide, seems to be the 

 most difficult to solve. 



As we have seen, the metal may be considered to exist in the form of vapour at the 

 moment of its reduction. Owing to the well-known affinity of aluminium for carbon 

 monoxide, t it is obviously important to remove this gas as completely and rapidly as 

 possible. 



A method of reducing the partial pressure of the carbon monoxide has been dealt 

 with above, and we have found it important to lead the gas used for dilution directly 



* J. N. PRING, -Trans. Chem. Soc.,' 1905, vol. 87, p. 1530. 

 t GUNTZ and MASSON, 'Comptes Rendua,' 1897, vol. 124, p. 187. 

 VOL. CCVII. A. 3 M 



