HELMHOLTZ ON THE CONSERVATION OP FORCE. 149 



metals to form a circuit among themselves. The absence of 

 special facts prevents us from making closer application of the 

 principle of the conservation of force in this case. 



The most complicated case is presented by those circuits in 

 which chemical decomposition and polarization take place side 

 by side ; to these belong the circuits in which gas is developed. 

 The current in these cases is strongest at the commencement, 

 and sinks more or less quickly to a point at which it remains pretty 

 constant. With single elements of this description, or with com- 

 pound batteries composed of such elements, the current of polari- 

 zation ceases with extreme slowness ; it is easier, on the contrary, 

 to obtain constant currents by combining constant elements with 

 inconstant ones, particularly if the plates of the latter be com- 

 paratively small. Hitherto however but few measurements have 

 been made with such circuits ; from the few which I have been 

 able to find by Lenz* and PoggendorfFf, it follows that the in- 

 tensity of such currents, when different resistances of wire are 

 introduced, cannot be expressed by the simple formula of Ohm ; 

 for when the constants are calculated from the low intensities, 

 the results for higher intensities are found to be too great. It 

 is therefore necessary to regard the numerator or denominator, 

 or both, as functions of the intensity ; the facts hitherto known 

 do not enable us to decide which of these cases really takes 

 place. 



In applying the principle of the conservation of force to these 

 currents we must divide them into two classes, into inconstant 

 or polarization currents, with regard to which, what we have 

 already expressed regarding the pure currents of polarization, 

 and constant or decomposing currents, is applicable. The same 

 mode of treatment is applicable to the latter and to the constant 

 currents in which no gas is developed; the quantity of heat 

 generated by the current must be equal to that due to chemical 

 decomposition. For example, in a combination of zinc with a 

 negative metal in dilute sulphuric acid, suppose the quantity of 

 heat liberated by an atom of zinc during its solution and the ex- 

 pulsion of the hydrogen «^— a^^, then the quantity of heat de- 

 veloped in the time dt would be 



\{a^^at)dt, 



* Pogg. ////w. liv. 229. t ^nn. Ixvii. 531. 



SCIEN. MKM.— A^«/. Phil, Vol. I. Part If. M 



I. 



