54 THEORY OF LIGHT. 



being its positive extremity, at which combustible bodies, 

 metals, alkalies, and bases are evolved, and is in contact with 

 the negative electrode. 



He declares as a result of his experiments, that water, 

 though a compound, formed of very powerful affinity, is most 

 susceptible of electrolytic action, and yields up its elements 

 under the influence of a very feeble electrical current. 



All known compounds being non-conductors when solid, but 

 conductors when liquid, are decomposed with the single excep- 

 tion of periodide of mercury, and even water itself, w r hich so 

 easily yields up its elements when the current passes, if ren- 

 dered quite pure scarcely suffers change, because it then 

 becomes a bad conductor, which argues the possibility that 

 decomposition depends upon conduction, and not the latter 

 upon the former ; a point which water seems nearly to decide. 



Although the mineral acids facilitate the conduction and 

 decomposition of water, that is no proof that they are competent 

 to favor and suffer these actions in themselves. 



Boracic acid effects the same thing, though not decomposable. 



M. De La Rive has pointed out that chlorine has this power : 

 though considered by us hitherto an elementary substance, it 

 ought to be capable of suffering decomposition or imparting it 

 to other bodies. 



Professor Faraday observes, in reference to one standard of 

 measurement of the common and Voltaic electricity, that the 

 chemical decomposing action of a current of either is constant 

 for a constant quantity 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-con- 

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



That exactly the same quantity of water was decomposed in 

 all the solutions by the same quantity of electricity, though the 

 sulphuric acid in some solutions was seventy -fold, what it was 

 in others. The highest strength used was of specific gravity 

 1.495, but that solutions of a gravity of 1.336 were the most 



