THE SMITHSONIAN INSTITUTION. 405 



in which they are immersed contain no free oxygen. Therefore, it is 

 clear that a Grove's battery must yield a current if one half the tube 

 is entirely filled with acidified water, while the other half contains 

 hydrogen, even if all free oxygen has been previously expelled from 

 the liquid, and the entrance of atmospheric air is prevented. 



This current will soon cease, because, in consequence of it, the 

 hydrogen disappears from the platinum plate not previously in con- 

 tact with gas, and, therefore, the difi'erence which caused the formation 

 of the current disappears. 



If the current is to continue, then the hydrogen escaping at the 

 other side, in consequence of the current, must be removed, and this 

 is, according to Schdnbein's view, the function of the oxygen in the 

 gas battery. 



Schonbein, therefore, holds the opinion, that oxygen does not act in 

 the gas battery as an electro-motor, but only as a depolarizer. He 

 sustains this opinion by the observation, the credibility of which is 

 unjustly disputed by the editor of the '' Jahresbericht von Liebig und 

 Kopp," that pure oxygen is unable to polarize a plate in the same 

 manner as hydrogen does. 



The numerical values before given for the polarization of platinum 

 plates in different gases, renders it possible to state the question in 

 precise terms. 



The entire polarization in a voltameter is at a maximum about 

 1200 ; one-half of this polarization is due to the plate coated with 

 hydrogen, the other half to the positive platinum plate coated with 

 oxygen containing ozone. Now the question is : Is the electro-motive 

 force of an element of the Grrove gas battery equal to 1200 ; or is it, 

 according to Schdnbein's view, only 600 ? 



Although a platinum plate coated with pure oxygen, combined 

 with another in acidified water, generates no current, yet there is 

 here always an electrical difference, even though it should not be suf- 

 ficient to bring about decomposition in the intermediate stratum of 

 water ; hence it is probable, that the electro-motive force of a Grrove 

 gas element, charged with hydrogen and pure oxygen, is greater than 

 (iOO, if it does not attain the value 1200. 



At the first glance, nothing appears easier than to decide this 

 question by measuring directly the electro-motive force of the gas bat- 

 tery ; but a closer examination shows that such a measurement is 

 utterly impossible. The platinum plates of the gas pile are not 

 entirely coated with gas, but only partially. Therefore, we have here 

 a similar case to that in which one of a pair of platinum places is 

 partially covered with zinc. By applying the difierent methods for 

 determining the electro-motive force of the current, which here" tra- 

 verses the wire connecting the platinum plates, we shall certainly not 

 obtain the true value of the electrical difference between zinc and pla- 

 tinum, (wholly disregarding the polarization which appears at the 

 clean platinum plate). On account of the partial coating of the pla- 

 tinum plate with gas, lateral currents are formed, so that the current, 

 which traverses the closing wire, is only a part'of the effect produced 

 by the electrical opposition in the battery ; hence, also, in part, the 

 exceedingly feeble force of the current in the gas pile. 



