DEFINITE CHEMICAL ACTION OF ELECTRICITY. 103 



a current of electricity is in direct proportion to the absolute quantity of electricity 

 which passes (377-) • 



784. In the further progress of the successive investigations, I have had frequent 

 occasion to refer to the same law, occasionally in circumstances offering powerful 

 corroboration of its truth (456. 504. 505.) ; and the present series already supplies 

 numerous new cases in which it holds good (704. 722. 726. 732.). It is now my object 

 to consider this great principle more closely, and to develope some of the consequences 

 to which it leads. That the evidence for it may be the more distinct and applicable, I 

 shall quote cases of decomposition subject to as few interferences from secondary re- 

 sults as possible, effected upon bodies very simple, yet very definite in their nature. 



785. In the first place, I consider the law as so fully established with respect to the 

 decomposition of water, and under so many circumstances which might be supposed, 

 if anything could, to exert an influence over it, that I may be excused entering into 

 further detail respecting that substance, or even summing up the results here (732). 

 I refer, therefore, to the whole of the subdivision of this series of Researches which 

 contains the account of the volta-electrometer. 



786. In the next place, 1 also consider the law as established with respect to mu- 

 riatic acid by the experiments and reasoning already advanced, when speaking of 

 that substance, in the subdivision respecting primary and secondary results (758, &c.). 



787- I consider the law as established also with regard to hydriodic acid by the 

 experiments and considerations already advanced in the preceding division of this 

 series of Researches (7^7' 768.). 



788. Without speaking with the same confidence, yet from the experiments de- 

 scribed, and many others not described, relating to hydro-fluoric, hydro-cyanic, ferro- 

 cyanic, and sulpho-cyanic acids (770. 771. 772.), and from the close analogy which 

 holds between these bodies and the hydro-acids of chlorine, iodine, bromine, &c., I 

 consider these also as coming under subjection to the law, and assisting to prove its 

 truth. 



789. In the preceding cases, except the first, the water is believed to be inactive ; 

 but to avoid any ambiguity arising from its presence, I sought for substances from 

 which it should be absent altogether ; and, taking advantage of the law of conduction 

 already developed (380. &c.), soon found abundance, amongst which protochloride of 

 tin was first subjected to decomposition in the following manner. A piece of platina 

 wire had one extremity coiled up into a small knob, and having been carefully weighed, 

 was sealed hermetically into a piece of bottle-glass tube, so that the knob should be 

 at the bottom of the tube within (fig. 13.). The tube was suspended by a piece of platina 

 wire, so that the heat of a spirit-lamp could be applied to it. Recently fused proto- 

 chloride of tin was introduced in sufficient quantity to occupy, when melted, about 

 one half of the tube ; the wire of the tube was connected with a volta-electrometer 

 (711.)j which was itself connected with the negative end of a voltaic battery; and a 

 platina wire connected with the positive end of the same battery was dipped into the 



