1895.J on the Rarer Metals and their Alloys. 503 



is present in cast iron, it protects the silicon, manganese and carbon 

 from oxidation.* The presence of silicon in aluminium greatly adds 

 to the brilliancy with which aluminium itself oxidises and burns.f 

 It is also asserted that aluminium, even in small quantity, exerts a 

 powerful protective action against the oxidation of the silver zinc 

 alloy, which is the result of the desilverisation of lead by zinc. 



Moreover, heat aluminium in mass to redness in air, where 

 oxygen may be had freely, and a film of oxide which is formed will 

 protect the mass from further oxidation. On the other hand, if 

 finely-divided aluminium finds itself in the presence of an oxide of a 

 rare metal, at an elevated temperature, it at once acts with energy 

 and promptitude, and releases the rare metal from the bondage of 

 oxidation. I trust, therefore, you will consider my claim that a 

 metal may possess moral attributes has been justified. Aluminium, 

 moreover, retains the oxygen it has acquired with great fidelity, and 

 will only part with it again by electrolytic action, or at very high 

 temperatures under the influence of the electric arc in the presence 

 of carbon. 



[A suitable mixture of red-lead and aluminium was placed in a 

 small crucible heated in a wind furnace, and in two minutes an 

 explosion announced the termination of the experiment. The cru- 

 cible was shattered to fragments.] 



The aluminium loudly protests, as it were, against being entrusted 

 with such an easy task, as the heat engendered by its oxidation had 

 not to be used in melting a difficultly fusible metal like chromium, 

 the melting point of which is higher than that of platinum. 



It is admitted that a metal will abstract oxygen from another 

 metal if the reaction is more exothermic than that by which the oxide 

 to be decomposed was originally formed. The heat of formation of 

 alumina is 391 calories, that of oxide of lead is 51 calories; so that 

 it might be expected that metallic aluminium, at an elevated tem- 

 perature, would readily reduce oxide of lead to the metallic state. 



The last experiment, however, proved that the reduction of oxide 

 of lead by aluminium is effected with explosive violence, the tem- 

 perature engendered by the reduction being sufficiently high to 

 volatilise the lead. Experiments of my own show that the explosion 

 takes place with much disruptive power when aluminium reacts on 

 oxide of lead in vacuo, and that if coarsely ground, fused litharge 

 be substituted for red-lead, the action is only accompanied by a 

 rushing sound. The result is, therefore, much influenced by the 

 rapidity with which the reaction can be transmitted throughout the 

 mass. It is this kind of experiment which makes us turn with such 

 vivid interest to the teaching of the school of St. Claire Deville, the 

 members of which have rendered such splendid services to physics 

 and metallurgy. They do not advocate the employment of the 



* Bull. Soc. Chim. Paris, vol. xi. 1894, p. 377. 



f Ditk-, ' Lcrous sur les Metaux,' part ii. 1891, p. 206. 



2 M 2 



