554 Intelligence and Miscellaneous Articles. 



M. Matteucci has recently called to mind an experiment which he 

 made in 1838, and on which he considers himself justified in assuming 

 that the polarization arises from the gas adhering to the electrodes. 

 I think that the polarized metals should be regarded as fugitive 

 combinations of the metals and the gases ; and I assume that in 

 polarization-elements, as well as in Grove's gas-battery, the electro- 

 motive force is the affinity exercised on one of the elements of the 

 water by the gas united in some special way to a metal ; there is, 

 however, a distinction to be drawn between the combination pro- 

 duced under the influence of a current and that formed simply from 

 the affinities of the metals put in juxtaposition. 



As I have already pointed out, a platinum plate immersed in a 

 saturated solution of oxygen developes no electromotive force, while 

 a platinum plate polarized by oxygen may develope in contact with 

 pure or acidulated water a force equal to 193 ; platinum, therefore, 

 under the influence of a current can form with gases combinations 

 different from that which they form simply in virtue of their affini- 

 ties. Let me add that platinum is the only body with which gas- 

 couples have hitherto been constructed, while all the metals may be 

 polarized by hydrogen when they are used as cathodes in the decom- 

 position of water. 



The distinction I have drawn appears to me useful in explaining 

 how two contrary polarizations may apparently superpose themselves 

 on one and the same electrode. Imagine acidulated water to be 

 decomposed by using two platinum electrodes A and B : if the cur- 

 rent be passed for ten minutes in one direction and then be turned 

 for an instant in the other, and then by means of a convenient com- 

 mutator the polarized electrode be rapidly connected with a galvano- 

 meter, at first a transitory deflection in one direction is obtained, 

 followed by a permanent one in the other. This fact, which may be 

 readily confirmed, may, I think, be explained in the following man- 

 ner : — When a current of tolerable duration passes through a liquid 

 from A to B, the electrode B is. polarized by the hydrogen, the 

 liquid which bathes the plate A becomes charged with oxygen, the 

 liquid surrounding B is charged with hydrogen. When the direction 

 of the current is inverted for a moment, the existing polarizations are 

 destroyed and inverse polarizations produced, but the condition of 

 the liquid layers surrounding the electrodes is not appreciably altered. 

 It thus happens that at the moment communication is made with the 

 galvanometer, the electrode A, polarized by hydrogen, is immersed 

 in a solution of oxygen, and that, on the contrary, the electrode B, 

 polarized by oxygen, is immersed in a solution of hydrogen. The 

 current which is observed at first is due to polarization properly so 

 called ; but as this polarization is very feeble, it is annulled in a few 

 seconds ; and when the plate B is deprived of the oxygen it had ab- 

 sorbed under the influence of the current, it combines, owing to its 

 affinity solely, with a portion of the hydrogen contained in the sur- 

 rounding liquid, and thus forms a gas-couple. — Comptes Rendus, Sep- 

 tember 9, 1867. 



