EPOCH OF DAVY AND FARADAY. 290 



conjectiire by Davy, and adopted as the basis of chemistry by Ber 

 jelius, could only be established by exact measures and rigorous proofs. 

 Faraday had, in his proof of the identity of voltaic and electric agency, 

 attempted also to devise such a measure as should give him a compa- 

 rison of their quantity ; and in this way he proved that 1 * a voltaic 

 group of two small wires of platinum and zinc, placed near each other, 

 and immersed in dilute acid for three seconds, yields as much electri- 

 city as the electrical battery, 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." 



It was in his " Seventh Series," that he finally established a principle 

 of definite measurement of the amount of electrolytical action, and de- 

 scribed an instrument which he termed" a volta-electrometer. In this 

 instrument the amount of action was measured by the quantity of 

 water decomposed : and it was necessary, in order to give validity to 

 the mensuration, 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 

 accuracy 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 amolint according to the 

 measurement of the new instrument." 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-electrorneter 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-electrometer, Faraday obtained, for each 

 elementary substance, a number which represented the relative amount 

 of its decomposition, and which might properly 94 be called its " electro- 

 chemical equivalent." And the question naturally occurs, whether 

 these numbers bore any relation to any previously established chemi- 

 cal measures. The answer is remarkable. They loere no other than 

 ihe atomic weights of the Daltonian theory, which formed the climax 

 of the previous ascent of chemistry ; and thus here, as everywhere in 



19 Researches, Art. 371. ao 537. n 739. 



22 Arts. 758, 814. 23 377. M 792. 



