A Theory of the Aluminium Anode. 30B 



it to be an aluminium suboxide ; but, later, came to the 

 conclusion that it is merely the ordinary oxide or hydroxide. 

 More recently Norden * showed that the film is the ordinary 

 hydroxide, Al (OH) 3 . Lawrie f had previously come to the 

 conclusion, based on experiments upon the effect of amal- 

 gamation on the electrochemical behaviour o£ aluminium, 

 that the peculiarities are due to a layer of oxide or of sub- 

 oxide. 



The subject has also been investigated by several physicists 

 who endeavoured to explain the physical peculiarities. At 

 first the film of oxide was supposed to act as a layer which 

 protected the electrode from the action of the electrolyte ; 

 but Oberbeck % and Streintz § suggested that the film acts 

 as a non-conductor, and that the electrode, the film, and the 

 electrolyte form a condenser ; and a condenser consisting of 

 two aluminium plates with a solution of a sulphate as 

 electrolyte has been described by Haagn ||. In all these 

 cases a neutral sulphate or sulphuric acid solution formed the 

 electrolyte, Streintz especially mentioning that in nitric acid 

 the behaviour of aluminium is quite normal. The question 

 became one of practical importance when Pollak H and 

 Gratz ** independently showed that a cell consisting of one 

 aluminium electrode and one carbon electrode in dilute 

 sulphuric acid could be used to change an alternating current 

 into a direct current, since the phase in which aluminium is 

 the anode is stopped by the cell. Various investigators ft 

 found that currents of 20 volts or even of 100 volts potential 

 can be so transformed. Later researches have not brought 

 to light many new facts, though Wilson % % showed that the 

 transformation is not complete if the period of alternation is 

 less than -j^ second. None of the investigators attempt to 

 explain how this film is produced and maintained. Nor den § § . 

 however, gives the following explanation : — When sulphuric 

 acid is electrolysed with an aluminium anode the secondary 

 oxygen produced acts on the anode to form Al (OH) 3 , which 



* Zeit.fur JElehtrocJwmie, vi. pp. 159, 188 (1899-1900). 



t Phil. Mag. f5] xxii. p. 213 (1886). 



X Wied. Ann. xix. p. 625 (1883). 



§ Wied. Ann. xxxii. p. 116 (1887) ; xxxiv. p. 751 (1888). 



|| Zeit.fur EleUrochemie, iii. p. 470 (1896-97). 



II Compt. Rend, cxxiv. p. 1443 (1897). 



** Wied. Ann. lxii. p. 323 (1897). 



ft Bleibliitter, xxiii. pp. 108, 502, 564 ; 650: Elektrotechn. Zeits. xxi. 

 p. 913. 



XX Electrical Review, 1898, p. 371: Proc. Roy. Soc. vol. Ixiii. p. 329 

 (1898). 



§§ Loe. cit. 



