THE RARER METALS AND THEIR ALLOYS. 503 



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 aluminum was placed in a small 

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

 announced the termination of the experiment. The crucible was shat- 

 tered to fragments.] 



The aluminum loudly protests, as it were, against being intrusted 

 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 aluminum, at an elevated temperature, would 

 readily reduce oxide of lead to the metallic state. 



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

 lead by aluminum is effected with explosive violence, the temperature 

 engendered by the reduction being sufficiently high to volatilize the 

 lead. Experiments of my own show that the explosion takes place 

 with much disruptive power when aluminum 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 teach- 

 ing of the school of St. Claire Deville, the members of which have ren- 

 dered such splendid services to physics and metallurgy. They do not 

 advocate the employment of the mechanism of molecules and atoms in 

 dealing with chemical problems, but would simply accumulate evidence 

 as to the physical circumstances under which chemical combination and 

 dissociation take place, viewing these as belonging to the same class of 

 phenomena as solidification, fusion, condensation, and evaporation. 

 They do not even insist upon the view that matter is minutely granu- 

 lar, but in all cases of change of state make calculations on the basis 

 of work done, viewing changed "internal energy" as a quantity which 

 should reappear when the system returns to the initial state. 



A verse of some historical interest may appeal to them. It occurs 

 in an old poem to which I have already referred as being connected 

 with the "Roman de la Rose," and it expresses nature's protest against 

 those who attempt to imitate her works by the use of mechanical meth- 

 ods. The " argument" runs thus: 



Comme Nature se complaint, 

 Et dit sa douleur et son plaint 

 A ung sot souffleur sophistique 

 Qui n'use que d'art mechanique. 



