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XXXVI. The Cause of the Production of Electricity by the 

 Contact of Heterogeneous Metals. By Prof. Franz Exner *. 



ri^HOUGH it has so often been experimentally proved that 

 -*- a difference of electric potential is produced by the contact 

 of heterogeneous metals, there has not as yet been given any 

 explanation of this phenomenon that will bear scrutiny. The 

 contact theory as well as the so-called chemical theory both 

 lay claim to this phenomenon, and the adherents of the two 

 theories are at the present day perhaps about equal. An in- 

 vestigation concerning the nature of galvanic polarization 

 has led me to a quite distinct view of the origin of the so- 

 called contact electricity, a view which will be verified by 

 the following experiments. In the above-mentioned inves- 

 tigation I have shown that the original cause of the polari- 

 zation-current is not to be looked for, as has heretofore been 

 generally assumed, at the contact of the electrodes with the 

 ions separated on them, but in the recombination of these 

 latter ; and the electromotive force of the current so produced 

 is measured by the he at- value of this combination, just as 

 the electromotive force of any galvanic cell is measured by 

 the heat-value of the chemical process going on in it. With 

 a so-called contact action the existence of the polarization 

 current, and obviously of every other current, has nothing- 

 whatever to do. 



When, therefore, the contact theory proved to be here per- 

 fectly inapplicable, and indeed superfluous, the idea at once 

 suggested itself, to undertake from this standpoint a criticism 

 of the first beginnings of this theory, i. e. the fundamental 

 experiments of Volta ; that is to say, the idea suggested itself 

 to seek for the cause of the production of electricity at the 

 contact of two metals, not in this contact, but in previous 

 chemical actions of the surrounding media on the surfaces 

 of the metals. Therefore, at the conclusion of the above 

 mentioned paper on polarization, in referring to the analogy 

 between tension series and oxidation series, I have expressed 

 the opinion that the so-called contact electricity is produced 

 by the oxidation of the metals in contact by the oxygen of 

 the air, after the same laws according to which, in galvanic 

 cells, electricity is evolved by the oxidation of the zinc. If 

 this supposition prove true (and it has proved true), the 

 electromotive force of two metals in contact in air must be 

 measured and expressed by their heats of combustion. 



The first attempt at a confirmation of this purely chemical 

 theory consists, then, in a comparison between the electro- 



* Translation of a paper in Wiedemann's Ann. der Physik und Chemie, 

 1880. Communicated by J. Brown ; Esq. 



