DAVY. 113 



which it passed, had been before known. Thus water 

 had been resolved into its two elements by the passing 

 of the fluid through wires whose points were opposite 

 to each other at a small distance. Nicholson had first 

 made this happy application of the voltaic pile ; but 

 he and others had been much disturbed by finding 

 other substances produced as well as oxygen and hy- 

 drogen gases. This perplexing circumstance was care- 

 fully investigated by Davy ; and he showed by a mas- 

 terly course of experiments, that these substances 

 owed their origin entirely to impurities in the water. 

 When it was quite pure, they wholly disappeared. 

 But he now proceeded farther, and found that when 

 the electric current is thus passed, there is always a 

 separation operated differently at the negative and at 

 the positive part of the current. The oxygen of the 

 water, for example, was accumulated round the positive 

 wire ; its hydrogen round the negative. So when a 

 neutral salt was subjected to the process, its acid was 

 evolved round the positive ; its alkaline base round the 

 negative wire. The same thing happened when a me- 

 tallic oxide was operated upon ; its oxygen went to the 

 positive, its metallic base to the negative side. The 

 oxygen, or the acid with the oxygen, went to the for- 

 mer ; the particles of the base were transferred to the 

 latter, along with the hydrogen of the water in which 

 the solution was made. But a still more extraordinary 

 phenomenon was observed. If there was a liquid in- 

 terposed between the two poles and the body to be 

 decomposed, the acid, or the oxygen, was found to pass 

 through that interposed liquid to the positive pole, the 

 hydrogen and the matter of the base to the negative 

 pole, and without acting upon the substance of the in- 

 terposed liquid. Thus suppose a vegetable colour 

 tinging the water in an intermediate cup, acid will 

 pass through it without reddening it, and alkali with- 

 out making it green. Nay, an acid will pass through 

 an alkaline solution, or an alkali through an acid, 



