DISCOVERIES BY MEANS OF THE VOLTAIC BATTERY. 483 



liquid ; brine, or a solution of salt in vinegar, or dilute 

 muriatic, sulphuric, or nitric acid, might be employed ; 

 but dilute nitric acid was found to answer best, and the 

 energy of the battery is proportional to the strength of 

 the nitric acid employed.' l 



Hardly had the voltaic pile or battery been invented 

 before various investigators employed it to make dis- 

 coveries. In the year 1800 Nicholson and Carlisle, by its 

 aid, discovered the voltaic decomposition of water ; Cruick- 

 shank, in the same year, found that the voltaic current 

 changed the colour of litmus ; and Dr. Henry electro- 

 lytically decomposed nitric and sulphuric acids, and re- 

 solved ammonia into its constituent gases. Hisinger 

 and Berzelius also, in the year 1803, discovered the phe- 

 nomena of transfer of the elements of water and of various 

 salts to the respective electrodes by the current. It was 

 by means of the voltaic battery that Sir H. Davy, in 1807, 

 isolated and discovered the alkali metals. ' Davy, having 

 thus got possession of an engine by means of which the 

 compounds whose constituents adhered to each other might 

 be separated, immediately applied it to the decomposition 

 of potash and soda, bodies which were admitted to be 

 compounds, though all attempts to analyse them had 

 hitherto failed. His attempt was successful. When a 

 platinum wire from the negative pole of a strong battery 

 in full action was applied to a lump of potash, slightly 

 moistened, and lying on a platinum tray attached to the 

 positive pole of the battery, small globules of a white 

 metal soon appeared at its extremity. This white metal 

 he speedily proved to be the basis of potash. He gave it 

 the name of potassium, and very soon proved that potash 

 is a compound of five parts by weight of this metal and 



1 Thomson, History of Chemistry, vol. ii. p. 254. 

 i i 2 



