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Art. XLI. — On the Electro-motive Poioer of Metallic Sulphides. By W. Skey, 

 Analyst to the Geological Survey of New Zealand. 



[Bead before the Wellington Philosophical Society, November 12, 1870.] 



In a paper read before the Society at its last meeting, I showed that the 

 metallic sulphides generally were such ready conductors of electricity that they 

 could perform all the functions of the negative pole of a galvanic battery ; and 

 I stated that, reasoning from analogy, it appeared these sulphides should among 

 themselves, in presence of saline solutions, form voltaic pairs having a decom- 

 posing effect upon certain metallic salts. 



In continuation of the subject, I have been investigating into this, and 

 the i-esults clearly showing such to be the case, I beg to communicate the fact^ 

 together with various particulars concerniug it. 



I will preface my statement by observing, that it is well known the mere 

 contact of heterogeneous solids of whatever kind, even to gypsum and amber, 

 as Pfaff observed, develop electricity, but of such feeble tension that very 

 delicate electroscopes are required for its detection; and just recently. Professor 

 Becquerel has proved the same feeble development of electricity occurs wHen 

 gold is placed in saline solutions having no affinity for it.''* '^' 



The object, therefore, of this communication is not to demonstrate for- ^ 

 these sulphides the possession of a property hitherto iinknown, but that they 

 are able to manifest this particular property to such an extent in those saline 

 solutions frequently having contact with them in a natural way, that they are 

 able by such development to produce several chemical reactions, and among 

 them to reduce certain metals from their soluble salts, — the possibility of 

 which should certainly be considered when we enquire into the production and 

 metamorphosis of minei-al veins and their metallic contents. 



Thus, when common iron pyrites and galena are placed in dilute acids or 

 saline solutions, within a short distance of each other, and connected by 

 platinum wires, with a solution of gold chloride contained in a separate vessel, 

 it will be found, after the expiration of a few hours, that the wire connected 

 with the galena has been well gilded over that end of it submerged in the gold 

 solution. 



Clearly therefore a voltaic action has been set up by these sulphides here, 

 the galena has substituted the zinc, or positive element, of our ordinary 

 battery arrangements, while the iron pyrites has substituted the negative one. 



Galena and sub-sulphide of copper form another voltaic pair-, in which the 

 galena is this time the negative element. 



Besides gold, these sulphides are also capable of reducing silver and 

 platinum from their acid, solutions, but not copper, unless the positive electrode 



* CJwmical News, July 8, 1870, p. 21. 



