Thermal Phenomena of Voltameters, 553 



duced by the voltameter during the decomposition of 1 equiva- 

 lent of substance is therefore 



-X=-/x 239000 + K, 



or 



X=^x239000-Tx— ( 7 ) 



d p w ' 



My research is divided into two parts. 



In the first part I give an experimental demonstration of the 

 formulae («), (ft), and (7), and I establish the laws, hitherto 

 misconceived, which regulate the development of heat in volta- 

 meters. The experiments related to sulphate of copper and 

 acidulated water; they led to the following conclusion : — 



"A voltameter introduced into the circuit of a battery weakens 

 the electromotive force, and thus destroys in the complete circuit 

 a quantity of heat which is always greater than what is re- 

 quired for the decomposition effected. The excess varies accord- 

 ing to circumstances ; but in every case a secondary action takes 

 place at the electrodes, whereby a quantity of heat is imparted 

 to the voltameter equal to the excess of heat destroyed. And, 

 finally, the sum of the various calorific effects of the voltameter 

 is equal to the heat absorbed by the decomposition which goes 

 on within it." 



This effect can be explained if we suppose that the substances 

 first formed at the electrodes, and which cause the polarization, 

 are unstable compounds which, like binoxide of hydrogen, evolve 

 heat by their decomposition. 



In the second part I have determined, according to equation 

 (7), the quantities of heat, X, absorbed by the decomposition of 

 1 equivalent of sulphate of copper, of water, of cupric chloride, 

 and of hydrochloric acid. 



In these experiments it is essential to avoid the local recom- 

 bination of the gases in the voltameter. To effect this, the posi- 

 tive electrode is placed inside a small closed pipe-bowl, luted 

 with wax to the end of a thin glass tube of equal diameter, 

 whereby the oxygen or chlorine liberated is conducted out of the 

 apparatus. 



For the electrolysis of chlorides, a rod of retort-carbon, dip- 

 ping into hydrochloric acid saturated with chlorine, is used as 

 the positive pole. 



The following Table gives the mean of the results obtained, 

 compared with the calorific equivalents of the same substances 

 in a state of solution, determined by Favre and Silbermann and 

 by myself (Comptes iRendus, July 4, 1864). 



Phil Mag. S. 4. No. 192. Suppl. Vol. 28. 2 



