172 Dr. Faraday's Experimental Researches in Electricity, 



f v. On a new Measurer of Volta-clcctricity. 



704'. I have already said, when engaged in reducing com- 

 mon and voltaic electricity to one standard of measurement 

 (377*.)? an d again when introducing my theory of electro-che- 

 mical decomposition (504?. 505. 510.), that the chemical de- 

 composing action of a current is constant for a constant quan- 

 tity of electricity, notwithstanding the greatest variations in its 

 sources, in its intensity, in the size of the electrodes used, in 

 the nature of the conductors (or non-conductors (307. f)) 

 through which it is passed, or in other circumstances. The 

 conclusive proofs of the truth of these statements shall be 

 given almost immediately (733. &c). 



705. I endeavoured upon this law to construct an instru- 

 ment which should measure out the electricity passing through 

 it, and which, being interposed in the course of the current 

 used in any particular experiment, should serve at pleasure, 

 either as a comparative standard of effect, or as a positive 

 measurer of this subtile agent. 



706. There is no substance better fitted, under ordinary 

 circumstances, to be the indicating body in such an instru- 

 ment than water ; for it is decomposed with facility when ren- 

 dered a better conductor by the addition of acids or salts; its 

 elements may in numerous cases be obtained and collected 

 without any embarrassment from secondary action, and, being 

 gaseous, they are in the best physical condition for separation 

 and measurement. Water, therefore, acidulated by sulphuric 

 acid, is the substance I shall generally refer to, although it 

 may become expedient in peculiar cases or forms of experi- 

 ment to use other bodies (843.). 



707. The first precaution needful in the construction of the 

 instrument was to avoid the recombination of the evolved 

 gases, an effect which the positive electrode has been found 

 so capable of producing (571. J). For this purpose various 

 forms of decomposing apparatus were used. The first con- 

 sisted of straight tubes, each containing a plate and wire of 

 platina soldered together by gold, and fixed hermetically in 

 the glass at the closed extremity of the tube (Plate I. fig. 5.) 

 The tubes were about eight inches long, 0*7 of an inch in dia- 

 meter, and graduated. The platina plates were about an inch 

 long, as wide as the tubes would permit, and adjusted as near 



* See Lond. and Edinb. Phil. Mag., vol. iii. p. 362.— Edit. 



f Ibid. p. 171. 



X This and every other number referred to in these Researches, from 564. 

 to 660., belong to the Sixth Series, noticed in Lond. and Edinb. Phil, Mag., 

 vol. iv. p. 291. — Edit* 



