Galvanic Pile, and Electromotive Forces. 503 



the small difference mentioned. Consequently calorimeter 

 No. 2 could not but indicate, as it actually did, a somewhat 

 greater development of heat ; and hence we are perfectly 

 justified in asserting that theory and experiment are, within 

 the limits of errors of observation, closely accordant with each 

 other. 



6. Sir W. Thomson and, subsequently, Bosscha made the 

 following experiment * : — Two equal voltameters are filled 

 with the same quantity of sulphuric-acid water, and then suc- 

 cessively inserted in the circuit of a powerful galvanic series. 

 The electrodes in one of the voltameters both consisted of 

 platinum ; but in the other the positive electrode only was of 

 this metal, while the negative consisted of amalgamated zinc. 

 Although the same current passed through both voltameters, 

 and consequently an equal amount of chemical decomposition 

 took place in each, yet the temperature rose much more 

 rapidly in the voltameter which has zinc for the negative 

 electrode than in the other. Bosscha regards the unequal 

 elevations of temperature in the two voltameters as occasioned 

 by the power of the zinc to transfer hydrogen from the active 

 to the ordinary state being different from that which platinum 

 possesses in this respect. 



I have repeated this experiment, and obtained the same re- 

 sult. By applying the mode of representation No. 2, it is 

 easy to find the cause of the different elevations of tempera- 

 tion. There is in each of the voltameters an electromotive 

 force which acts in the opposite direction to the current of the 

 series. In the voltameter of which both the electrodes con- 

 sist of platinum this force originates exclusively from the 

 polarization of hydrogen and oxygen. In the other volta- 

 meter oxygen is separated at the platinum, and hydrogen at 

 the zinc ; but, besides the polarization hence arising, this 

 voltameter acts also as a pile, in the opposite direction to the 

 current. That the platinum-zinc vessel develops a greater 

 counterforce than the other vessel, one can easily convince 

 one's self by first inserting the one vessel in the circuit of the 

 current, and then withdrawing it and putting the other in its 

 place. One then finds that the current of the series is con- 

 siderably more enfeebled by the platinum-zinc vessel than by 

 the other. The quantity of heat arising from the current 

 passing in the opposite direction to the electromotive force 

 which acts in the two voltameters, must on that account be- 

 come greater in the platinum-zinc vessel than in the other. 



From what has been here alleged it follows that the thermal 

 phenomena in the pile, as well as in the voltameter, can be 

 * Pogg. Ann. vol. ciii. p. 487. 



