302 Dr. Taylor and Mr. Inglis : 



The primary object of this investigation was to find an 

 explanation of this anomalous behaviour of sulphuric acid, 

 and of the effect produced by the addition of chloride. It 

 has long been known * that., when an aluminium electrode is 

 employed as anode in a solution of a sulphate or of sulphuric 

 acid, there is a very great resistance offered to the current. 

 and that this resistance is due to a film which separates the 

 electrode from the solution. If the aluminium is the cathode, 

 or if other acids are substituted for sulphuric acid, this great 

 resistance does not exist. The film cannot merely act as a 

 dead resistance, for the resistance is different according to 

 the direction of the current. It seems probable, then, that 

 the two phenomena are related, and that the film is also the 

 cause of the slow action of sulphuric acid on aluminium. 

 This paper is an attempt to find an explanation which will 

 satisfactorily account for all these phenomena. 



Historical Summary. 



The behaviour of aluminium as anode in dilute sulphuric- 

 acid has been the subject of many investigations, but they 

 have been mainly directed to proving the existence of the 

 abnormalities, and not to finding the cause of them. The 

 earliest measurements appear to have been made by TVheat- 

 stone t. who tried to ascertain the position of aluminium in 

 the voltaic series. He found that its position depended on 

 the electrolyte used, and he noticed e-pecially the slight 

 action of nitric acid and of sulphuric acid, and the small 

 current obtained with the latter acid. His experiments were 

 repeated in greater detail by Burf'lj;. who observed remarkable 

 peculiarities with dilute sulphuric acid as the electrolyte. 

 He found on electrolysis of dilute sulphuric acid with an 

 aluminium anode and an external battery, that the anode 

 became covered with a dark skin which he supposed to be 

 silicon. Tait § investigated the polarization of the alu- 

 minium cell, using a variable polarizing battery. If six 

 Grove's cells formed the polarizing battery, the reverse E.M.F. 

 was V20 Daniells : in thi- case the polarizing E.M.F. was 

 10'44 D. As his measurement- were made with a Thomson 

 electrometer, they were independent of resistance. 



The dark skin first observed by Buff was the subject of 

 several investigations made by Beetz [ . He at first supposed 



* Buff. Liet^'s Annalen, cii. p. 269 (1857). 

 t Phil'. Mag. [4] x. p. 143 (1854). 



J Loc. cit. 



\ Phil. Mag. [4] xxxviii. p. 243 (1869). 



Pogg. AnrtaJen, vol. cxxvii. p. 4o : vol. clvi. p. 464 : 1877, vol. LL 

 p. 94. 



