Skey. — On the Oxidation of Mercury. 



587 



twenty years ago,* that a great number of cases cited by 

 Professor Becquerel and others of the polarisation of certain 

 noble metals by the viechanical absorption of oxygen are 

 really cases rather of polarisation by chemical absorption — 

 — that is to say, by oxidation. 



To challenge investigation of the correctness of my asser- 

 tions as to the general oxidation of all metals in solutions of 

 this nature, and to give what I think may be a useful table, I 

 append here one showing the relative affinity of twelve of 

 the principal metals for oxygen in solutions of potash and 

 sodic chloride respectively. Also, for comparison therewith, 

 I append an extract of a table of mine from our Transactions 

 showing the behaviour of these metals in potassic cyanide. 



The Electro motive Obder op Tvpelve Metals in Three Different 

 Solutions, from Negative downward to Positive. 



In potash, mercury is feebly positive to galena and strongly 

 negative to chalcopyrites ; while manganese binoxide is nega- 

 tive to the whole series in potash and potassic cyanide. In 

 ammonia and sulphate of magnesia (for a conducting medium) 

 platina paired with gold does not produce an electric current 

 that I could detect.! 



In concluding this section of my notes, I should not omit 

 to remark upon the singularity of the results Nos. 4 and 5, 

 where iron in alkaline solution is positive to itself in acid 

 solutions. So singular indeed did this appear to me that I 

 extended this investigation to include other metals in like 

 solutions within its scope, to find that a number of metals, 

 including platina, copper, lead, and zinc, gave like results to 

 these. That metals should comport themselves in this manner 

 is to me difficult to explain, and I would like to hear of the 



* Trans. N.Z. Inst., vol. viii., p. 342. 



t I should state here that in this solution gold was at first momen- 

 tarily negative to the platina. 



