146 Dr. Helmholtz on Galvanic Polarization --■ 



powerful at the commencement, under the ordinary conditions 

 of observation, but mostly soon dwindles to imperceptibility. 



It is this simple experiment to which my investigations refer. 

 The question to be solved was, On what depends the apparently 

 unlimited duration of the polarizing current ? for in a series 

 composed as above described, unless other changes also occur in 

 it, the electrolytic conduction which results according to Fara- 

 day's law in the liquids cannot take place without infringing 

 the law of the conservation of energy. That is to say, if no 

 other equivalents of potential energy are expended, in such a 

 series the mechanical equivalent of the heat generated in the 

 circuit must be equal to the work equivalent of the chemical 

 forces which become active and are expended in electrolysis. 

 The latter, however, if the decomposition proceeds according to 

 the law of electrolytic equivalents, is negative*, and therefore 

 cannot be equal to a positive heat-work to be produced by the 

 current. If, then, Faraday's law is exclusively valid, the decom- 

 position of water, even in the minutest quantity, cannot be 

 maintained continually by a DanielPs element. Indeed no dis- 

 engagement of the gases of which water is composed is observed 

 in the above-described experiment, however long the current 

 lasts. 



It is moreover to be remarked that not even by diffusion or 

 any process similar to diffusion could the molecules of hydro- 

 gen and oxygen, which on the polarization of the plates are 

 urged towards them, become free and, again unelectric, remove 

 from them. Such an occurrence would finally give, as the re- 

 sult of the work, a water-decomposition for which no equivalent 

 inciting force would be present in the Daniell's element. If, as 

 is probable, on the polarization of the electrodes a changed ar- 

 rangement of the atoms of hydrogen and oxygen enters, whether 

 in the interior or at the boundary surfaces of the liquid, these 

 particles are at all events kept in their places by chemical or 

 electric forces of attraction till new forces come to aid of suffi- 

 cient power to set them free. "Whatever relations between elec- 

 tric and chemical attraction-forces may be assumed, if the law 

 of the conservation of energy holds good, an electric attraction 

 upon one of the elements, whose potential is sufficiently great to 

 overcome the chemical affinity, can itself be again overpowered 



* According to Andrews, 1 gramme of hydrogen in burning to water gives 

 33,808 heat units ,• according to Favre and Silbermann, 34,462. For each 

 gramme of hydrogen, in the Daniell's element, 32*5 grm. of zinc are dis- 

 solved, and the equivalent amount of copper precipitated. This quantity 

 of zinc, when it separates copper from combination with sulphuric acid, 

 generates, according to Favre, only 23,205 units of heat. Corresponding 

 to this, an electromotive force of at least 1| Daniell's element is requisite 

 in order to maintain even the feeblest lasting decomposition of water. 



