TRANSACTIONS OF THE SECTIONS. 395 



no other meaning than the substance or surface which hmits 

 the decomposing body in the direction of the electric cm-rent. 



It then became an object to produce a water pole, and by 

 much care this was effected. A strong solution of sulphate of 

 magnesia was so adjusted as to have pure water floating upon 

 it over one half of its surface ; a platina plate was dipped hori- 

 zontally into this water, and another placed vertically in the 

 half of the solution of magnesia uncovered by water ; so that 

 the order of things were, platina, sulphate of magnesia solution, 

 pure water, platina: the first platina was rendered positive, 

 and the latter negative, by contact with a voltaic battery. Im- 

 mediately there was decomposition both of the water and of 

 the salt present ; the water yielded its elements against the 

 platina pole, but the salt could not do so. It is true the acid 

 appeared against the positive pole, but the earth magnesia 

 appeared in the plane where the solution and water were in 

 contact ; in fact, upon the surface of water next the decom- 

 posing solution, and not upon the negative platina pole. Here, 

 therefore, a true water pole was obtained, ^. e. a surface of 

 water upon or against which the earth magnesia evolved in a 

 case of electro-chemical decomposition was deposited. 



These were considered as very important facts in determining 

 the true character of the action taking place in cases of electro- 

 chemical decomposition generally. 



Another correction of commonly received opinions was con- 

 sidered as essential in assisting to determine the nature of 

 electro-chemical action. It has been generally stated by Sir 

 Humphry Davy and others, that water is essential to decom- 

 position by the voltaic battery; but Mr. Faraday has shown that 

 such is not the case, and that an immense number of other bodies 

 have, not merely equal powers, but powers far surpassing those 

 of water in that respect. The cause of this mistake has been 

 our ignorance of a law developed in the fourth series of the 

 Experimental Researches, under which an extensive class of 

 compound bodies, such as oxides, chloi'ides, iodides, salts, &c., 

 which are either very bad or nearly non-conductors when solid, 

 become most excellent conductors when melted, and then are 

 decomposed with extreme facility. Water happens to be the 

 only one of this class of bodies existing naturally in the fluid 

 and therefore decomposable state : it loses this power when it 

 becomes a solid, and other bodies gain it when they become 

 fluid. Electro-chemical decomposition does not therefore, of 

 necessity, involve the pi-esence of water. 



For the purpose of making his own view of matters clear 

 and distinct, Mr. Faraday gave a brief view of the theories of 



