233 



is of some metal having an affinity for the acicl of the aohition, so that in the 

 case of this metal it is not so much a decomposition as a transference which 

 takes place.* 



With a zinc and platinum pair even, in sulphu.ric acid, it is only possible 

 to reduce copper by this kind of transference, at least with common tempera- 

 tures ; so that this inability of metallic sulphides to reduce copper under these 

 circumstances, is no indication of their inferiority to zinc in respect to the 

 intensity of their electro-motive power. 



In these experiments the wires were connected with the minerals well 

 above the water line, and the suiface of the latter kept dry to this line, so 

 that the effects described were unmistakably due to the sulphides themselves 

 acting upon tlie liquid around them. 



Other sulphides manifest the same behaviour when dissimilar ones are 

 paired in this manner. 



The annexed column represents those which have been tested up to this 

 date, stated in the order of their positiveness relative to each other in sea 

 water. Any two of these, connected as I have described, will be found to be 

 positive and negative respectively ; and that occupying relatively the highest 

 f)osition in this column will always p^ove to be the positive one. 



* The electro-deposition of copper upon a platinum plate, by means of a sulphide pair 

 in sea-water (copper being the ]3ositive electrode for reasons above given), was exhibited 

 at the close of the meeting, when, in the discussion which arose upon it, Mr. Hamilton, 

 a member of the Society present, urged that the electrolytic effects produced were not 

 due to the sulphides, but rather to the copper and platina used ; these plates with the 

 associated solution of copper sulphate beiug maintained by Mr. H. with great persistency, 

 and against much remonstrance on my part, to form in this case ' ' both the battery and 

 decomposition cell, the sulphides employed merely completing the interpolar connection 

 between these copper and platina plates. " 



This opinion being publicly expressed, and adhered to, I feel obliged to notice it, as it 

 challenges the correctness of all which this paper was designed to convey and support, 

 and thus has the effect, or at all events the tendency, to lead the Society to suppose I 

 am in the habit of preparing papers for it, constructed so carelessly, and founded upon 

 errors so gross and palpable, that anyone thinking and speaking at random may disprove 

 them. All I need say in self-defence is, that I do not know of anything in the science 

 of electricity which at all warrants such a view as that expressed by Mr. Hamilton 

 being entertained ; but for his satisfaction, I have repeated my experiments, and 

 with such modifications that rendered it, if possible, a still more crucial test of the 

 correctness of my statements — the results, it is needless to say, were quite at variance 

 with those Mr. H. indicated. Thus, if we place a piece of copper, and one of platinum, in 

 solution of sulphate of copper, and connect them directly with each other, we find that 

 the platinum will not become coated with copper. If, then, no electrotypic effect is 

 produced when the connection between the plates is metallic, it %viU be obvious that 

 such effects would not be produced were (as in my demonstration) the electric resistance 

 increased by the interposition of sulphides, and a thickness of salt water in the circuit, 

 both being inferior conductors as compared to copper or platinum. 



2 H 



