Hydrogen from the Anode. 277 



oxygen and no hydrogen; the current is so weakened that it is 

 nearly reduced to nil. Buff regarded this incrustation as sili- 

 cium. The formation of a coating of silicium is undoubtedly 

 quite conceivable; for our aluminium always contains some. I 

 have, however, a reason for not regarding this film as silicium : 

 pour some silicium powder into a glass tube the lower end of 

 which is closed with parchment paper; dip this end into dilute 

 sulphuric acid ; then place one aluminium wire in the acid and 

 another in the silicium, and in every case the silicium is found 

 to be positive towards the aluminium. It matters not in this 

 experiment which of the wires be first dipped in the solution, 

 the aluminium wire immersed in the acid is invariably negative. 

 If the current be weak on account of the bad conducting-power 

 of the silicium, it is only necessary to press the aluminium wire 

 strongly against the powder in order to bring its particles more 

 closely in contact with one another — a method previously adopted 

 by me when using substances in a pulverized state*. The sili- 

 cium which I employed was crystalline. Amorphous silicium 

 was not readily procurable at the time, though I had a body 

 which comports itself in a precisely analogous manner — amor- 

 phous boron. This body, when treated in the same manner with 

 aluminium wires, was also distinctly positive. The badly-con- 

 ducting incrustation therefore could hardly be silicium ; I regard 

 it, on the contrary, as a suboxide of aluminium. At all events 

 this suboxide is a very bad conductor, it consequently does not 

 give rise to the formation of local currents ; and it does not dis- 

 solve in dilute acids. If, on the other hand, from the possibility 

 of forming basic salts, it be predisposed to further oxidation, it 

 gives rise to just the same phenomena as the suboxide of mag- 

 nesium ; and consequently the explanation given by Wohlerand 

 Buff, for the only case which concerns us here, of the anomalous 

 formation of hydrogen is the correct one. 



Bufff entertains the same view of the passive state of the 

 metals which is upheld by me J. He finds in a very insoluble 

 layer of oxide or in a film of oxygen, protecting the metal from 

 further attack, the cause of the passive state. The formation of 

 a suboxide on the surface of a metal which is known to possess 

 the property of passivity to a high degree, appears to me to give 

 additional support to this view. 



Henrici found, in his experiments on the effect of motion of 

 metallic wires in liquids, that aluminium comports itself in a 

 totally different way from other metals. In explanation of this 

 anomalous behaviour, he says§, " If it be assumed that the alu- 



* Poggerulorff's Annalen, vol. cxi, p. G19. 



t Ann. der Chem. und Pharm. vol. cii. p. 2G5. 



J Poggendoiff's Annalen, vol. lxvii. p. 186. § Ibid. vol. cxxi.p. 496. 



