250 



KNOWLEDGE. 



JlI,Y. 1911. 



Goldschmidt was able to prepare many other metals 

 (in a fused condition). Moreover, [providing that the 

 oxide was present in slight excess of the amount 

 chemically equivalent to the quantity of aluminium 

 emplo\ed. the corresponding metal was obtained in 

 a state of exceptional puritv. free from carbon. By 

 using mixtures of oxides. allo\'s of desired composition 

 were similarlv obtained. It seems, indeed, that 

 practicalh- all metallic oxides will react in this 

 manner with aluminium. In some cases. t'.,i,'.. 

 titanium and vanadium, in which pure metals are not 

 obtained, the product is sufficiently pure for the 

 preparation of the chlorides. Even calcium oxide 

 (lime) is not entirely proof against the activity of 

 aluminium, though the reaction between these two 

 bodies can onlv be brought about when they are 

 heated together in a furnace, and is then by no 

 means complete. It seems, therefore, to differ from 

 the reactions between aluminium and other metallic 

 oxides in being endothermic (i.e., heat-absorbing), 

 and it mav be concluded that calcium has a greater 

 heat of combustion than aluminium (measured, of 

 course, with respect to the same quantity of 

 oxN'gen).* Magnesia, however, is quite imattack- 

 able b\' this most active element. With alumina 

 itself, aluminium \'ields a blackish-grey [)roduct. 

 [)robabl\" containing a sub-oxide. 



Aluminium reacts in a similar manner with the 

 sulphides of the metals. Thus, with galena (lead 

 sulphide) the ])roducts are lead and aluminium 

 sulphide, as shown b\' the following eijuation. — 



3PbS-K2Al = .\l.,S.,+3Pb. 

 This reaction ma)- be employed for the preparation 

 of aluminium sulphide t which cannot be obtained in 

 the wet wav, since it is decomposed b\' water, giving 

 aluminium hydroxide and sulphuretted hydrogen) 

 which is obtained pin^e if the ahuninum is present 

 in slight excess."'' This excess of aluminium also 

 serves to free the lead from aii\' metallic impuri- 

 ties, for \\hilst aluminium will not allo\- with lead. 

 it readiK' allovs with man\- other metals. If 

 aluminium were cheaper, the method might be 

 used commercially for the extraction of traces of 

 the precious metals from lead ores. 



.Muminium will also react with certain non- 

 metallic oxides {e.g. boron trioxide and silica). In 

 the former case the product of the reaction 

 contains ahuninium lioride and aluminium nitride 



(the nitrogen coming from the air) as well as 

 alumina and free boron.; In the latter case 

 impure silicon is obtained as a crvstalline substance 

 containing aluminium. Aluminium will also react 

 with charcoal : in this reaction the air seems to pla\- 

 an important part, the product containing aluminium 

 oxide and nitride, as well as aluminium carbide 

 (Al^C:,) together with unchanged aluminium and 

 carbon.!; 



Since Goldschmidt's discovery. man\' other re- 

 actions, similar to those between aluminium and 

 metallic oxides, in which substances other than 

 aluminium are emploved, have been described. Dr. 

 F. M. Perkin, for example, has succeeded in bringing 

 about the reduction of metallic oxides and certain 

 other substances (e.g., galena and borax) by 

 means of metallic calcium. Dr. Goldschmidt has 

 also carried out experiments with this metal : he finds 

 that it reacts with oxides in a most violent manner, 

 but a regulus of metal is not formed ow ing to the 

 limited fusibility of the calcium oxide produced. He 

 finds, also. that, whilst silicon alone vields unsatis- 

 factory results, a mixture of calcium and silicon reacts 

 with metallic oxides in a satisfactorv manner. gi\ing 

 a fusible slag of calcium silicate.*^ 



Another substance. heha\ing in a similar manner. 

 is calcium hydride (CaHo). Dr. F. M. Perkin finds 

 that a mixture of this substance and cupric oxide 

 tin the proportion of two molecules of the oxide to 

 one of the h\'dride) can be readily ignited : volumes 

 of steam are evolved and copper is produced, but the 

 temperature is insufficient to melt the whole of the 

 copper. .A mixture of antimony sulphide and calcium 

 hydride is also \'er\' eas\' to ignite. .\s the reaction 

 proceeds, the mixture swells up in a manner similar 

 to that in which mercurv thiocvanate C Pharaoh's 

 serpents") behaves when heated.** 



Messrs. F. E.Weston and H. R. Ellis have carried 

 out a series of experiments on " thermitic reactions '" 

 (as these reactions are called) /// vacuo. Their final 

 form of apparatus is shown in Figure 1. They found 

 considerable difficult\ in igniting the mixtures 

 experimented upon, but this was probably due to the 

 difficultvof producing a sufficientl}' high temperature 

 //; vacuo. They succeeded, however, in obtaining 

 reaction in vacuo between magnesium and sodium 

 peroxide and between aluminium and sodium per- 

 oxide h\ ignition with a platinum wire electricall}- 



* F. E. Weston and H. R. Ellis: "The Heats of Combustion of Aluminium. Calcium and Magnesium." Transactions of the 



Faraday Society, (lOOS). \'ol. IV.. pp. loO ct scij. 

 I In this reaction the mixture may be heated in a crucible furnace with the cover off: but the aluminium should not be too 



finely powdered, as otherwise the heat generated may be sufficient to volatilise the lead. gi\ing rise to an explosion. 

 ; F. i:. Weston and H. R. Ellis: " Note on the Action of Aluminium Powder on Silica and Boric .Anhydride," Transactions 



of flic Faraday Society, 11907). Vol. III., pp. 170 et seq. 

 } F. !•:. Weslun and H. K. ICUis : " The Interaction of Aluminium Powder and Carbon," Tr,insactions of the Faraday 



Society, (1908), Vol. I\\. pp. 60 et seq. 

 ii F. .\I. Perkin: " Reduction of Oxides, Sulphides. lS:c., by Metallic C:dciuiu." Transactions of the Faraday Society 11907). 



\'ol. III., pp. 115 et seq. 

 • English P:itents, 7SH. Jan. lUh. I'JOO. 

 •■•" F. M. Perldn and L. PnUl : " Reducing Action of Metallic Calcium and Calcium Hydride upon Metallic Oxides. Sulphides and 

 Halogen Salts." Transactions of the Faraday Society (19071, Vol. HI., pp. 179 et seq. 



