186 HISTORY OF CHEMISTRY. 



charged by ten turns of a large machine ; and this 

 was established both by its momentary electro- 

 magnetic effect, and by the amount of its chemical 

 action 20 . 



It was in his " Seventh Series," that he finally 

 established a principle of definite measurement of 

 the amount of electrolytical action, and described an 

 instrument which he termed 21 a wlta-electrometer. 

 In this instrument, the amount of action was mea- 

 sured by the quantity of water decomposed : and it 

 was necessary, in order to give validity to the men- 

 suration, to show (as Faraday did show) that neither 

 the size of the electrodes, nor the intensity of the 

 current, nor the strength of the acid solution which 

 acted on the plates of the pile, disturbed the accu- 

 racy of this measure. He proved, by experiments 

 upon a great variety of substances, of the most 

 different kinds, that the electro-chemical action is 

 definite in amount according to the measurement 

 of the new instrument 22 . He had already, at an 

 earlier period 23 , asserted, that the chemical power of 

 a current of electricity is in direct proportion to 

 the absolute quantity of electricity which passes ; but 

 the volta-electrometer enabled him to fix with more 

 precision the meaning of this general proposition, 

 as well as to place it beyond doubt. 



The vast importance of this step in chemistry 

 soon came into view. By the use of the volta-elec- 



20 Researches, Art. 537- 21 739. 



92 758, 814. 23 377. 



