ON VOLTAIC BATTERIES. 683 



The maximum work which can be utilised per second is then 

 simply proportional to the number of couples, whatever is their 

 arrangement, and the value of the maximum work of each couple, 



e 2 

 or its mechanical power, is- . This number is characteristic of 



4r 



the couple in question. The value of e only depends on the nature 

 of the bodies which constitute the couples ; that of r depends, on 

 the contrary, on the shape of the elements, and on their dimensions. 

 In the ordinary couples, the electromotive force e rarely attains 

 2 volts. The resistance r varies, on the contrary, within wide limits ; 

 the smallest values are obtained with Grove's or Bunsen's elements, 

 and accordingly they are used when the battery has to do much 

 work. 



The mechanical power which corresponds to unit of electrical 

 work per second is now often called a watt ; according to this 



definition, a watt is equal to x , or about of a horse- 



9'8i 75 736 



power. A Bunsen's element, for instance, for which e = i '& volt, 



and r=o'oi ohm, would have a mechanical power of 81 watts, dr 



- of a horse-power. 

 9 



1242. CHEMICAL EXPENDITURE. Let p be the chemical equi- 

 valent of one of the bodies which plays a part in the action that 

 is to say, the weight of this body, which corresponds to an ampere 

 per second, or a coulomb; for a total current of intensity I, the 

 weight of this body, which comes into play in each couple in unit 



time, is p - . The weight P for the entire pile, for the time /, is then 



and the energy corresponding to this chemical action, expressed in 

 kilogram metres, is , 



' 



9 -8 1 9 -8 1/ 



The chemical energy, as might be foreseen, is independent of 

 the time of the operation, of the number, and arrangement of the 



