Chemistry". — "Tlie Electromotive Bt'li(ivi(yay of Magnes'nan" .\\^). 

 By Plot'. A. Smits. (Communicated In- Prof. P. Zeeman). 



(Communicated at the meeting of March 24, 1923). 



[utvodvction. The fact tliat llie rest |>oteiitials of magnesium and 

 aluminium in aqueous sointions of tlieir salts are too small ne^ntive 

 lias been the subject of frequent comment. 



An apparentij succesful explanalion was that which assumed the 

 presence of a film of oxide on the melal. This was however due 

 to a not snfïicieiitiy careful examination of the consequences of such 

 a premise. 



This is especial!}' true in the case of aluminium whei'e it had 

 been supposed, that the etched or even the polished metal was 

 coated with a not porous film of oxide of molecular thickness. 



Now a number of dilTerent in\estigations have proved with cer- 

 tainty tiiat if an etched or polished aluminium electrode is immersed 

 in mercury above which there is an aqueous solution of the alu- 

 minium salt, the aluminium immediately shows the potential of the 

 mercury layer, whilst there was no indication of the penetration of 

 a film of oxide '). 



It foHows from these investigations that either a film of oxide 

 does not hinder the passage of the electrons or there is no film at all. 



If the electrons only were going through an oxide layer we should 

 expect the behaveour of a gas electrode. This is not in accordance 

 with the fact. Consequently if the oxide film existed it would be 

 penetrable for ions, but it is then manifest that we are dealing with 

 a metal-electrode. 



Now it is possible that under certain circumstances the liquid in 

 the li([uid bounding layer is saturated with respect to the hydroxide 

 of the metal. This could easily be proved by the fact, that in the 

 formula 



0.058 , Lm 

 E = log.^ 2.8 (1) 



1) The considerations applied liere are explicated in the book "Theory of Allo- 

 tropy". Longmans, Green and Go. 1922. 



The first Communication appeared These Proc. Vol. XXII, 876 (192U). 

 ») See Zeitschr. f. Electr. Chem. 27, 523 (1921) and 28 (1922). 



26 

 Proceedings Royal Acad. Amsterdam Vol. XXVI. 



