276 Mr. J. P. Joule on the Heal evolved by Metallic 



oxygen may be considered almost decisive of the question. 



In his unexceptionable experiments, one grain of hydrogen 



produced heat sufficient to raise one pound of water 9 0, 6. 



Now we know from Exp. 5, that the heat generated in one 



4*77 x 32*3 

 of Mr. Grove's pairs by the electrolysis of = 25'7 



grains of zinc, is theoretically 3 0, 46 ; and the heat which must 

 in the same time have been generated by the metallic part of 



the circuit, which presented the resistance 0*06, is _ 



x 3 0, 46 = 0, 48 : the total voltaic heat was therefore 3 0, 94. 



Hence the total heat which would have been evolved by the 



32*3 

 electrolysis of an equivalent, or 32*3 grains of zinc, is -— - 



X 3 0, 94 = 4°*95 ; which, when reduced to the capacity of 

 one pound of water, is 9 0, 9. But from the table of the in- 

 tensities of voltaic arrangements (74-.), the intensity of Mr. 

 Grove's pair, compared with the affinity of hydrogen for oxy- 

 gen, is— \-\ whence, from (70.), we have 9°'9X0'93 = 9°% 



the heat which should be generated by the combustion of one 

 grain of hydrogen, according to the doctrine of resistances : 

 the result of Crawford is only o, 4 more. 



73. I am aware that there are some anomalous conditions 

 of the current which seem to militate against the general law 

 (68.), particularly when in the hands of Peltier it actually 

 produces cold*. I have little doubt, however, that the ex- 

 planations of these will be ultimately found in actions of a 

 secondary character. 



Note on Voltaic Batteries. 



74. In the foregoing investigation I have had occasion to 

 work very extensively with different voltaic arrangements, 

 and have repeatedly ascertained their relative intensities by 

 the mathematical theory of Ohm. It will not, therefore, I 

 hope, be deemed out of place to subjoin a table, in which the 

 intensities of the batteries which are most generally used, are 

 inversely as the number of pairs which would be just requisite 

 in order to overcome the resistance of water to electrolyza- 

 tion. 



* If antimony and bismuth be soldered together, cold will be produced 

 at the point of junction by the passage of the current from the bismuth to 

 the antimony. Peltier, Annates dc CIrimie, vol. lvi. p. 371. In his paper, 

 however, a misprint has inverted the direction of the current. 



