272 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP 



pairs of discs, whilst the efficiency of each unit was much 

 improved by replacing the wet cards by vessels of wood, 

 earthenware or glass, arranged side by side and filled with 

 brine, or with dilute alkali (Fig. 44) ; each CELL of the 

 BATTERY contained a zinc and a copper plate separated by a 

 layer of solution, the zinc and copper plates of adjacent cells 

 being soldered together. 



Nicholson and Carlisle (1801) decompose water by the 

 electric current. Nicholson and Carlisle discovered in 1801 

 that two platinum wires, attached to the terminal plates of a 

 voltaic pile and dipped in a glass of water, became 

 covered with bubbles of gas. Closer examination showed 

 that the gas collected from the positively-charged wire 



FIG. 44. THE VOLTAIC BATTERY OR "CROWN OF CUPS." 



Plates of zinc, z z, and copper or silver, A A, are soldered together at a a and 

 immersed in cups of brine. 



attached to the zinc plate of the pile, was oxygen, and that 

 hydrogen was liberated from the negatively-charged wire 

 attached to the silver plate of the pile. At the end of 

 13 hours, 72 grain-measures of oxygen and 142 grain- 

 measures of hydrogen were collected, i.e. " nearly the 

 proportions in bulk of what are stated to be the component 

 parts of water" (Nicholson's Journal, 1801, IV. 186). The 

 electric current had thus been able to overcome the affinity 

 of oxygen and hydrogen for one another, and had caused 

 both gases to be liberated in the free state. The discovery 

 of the decomposing power of the electric current was of 

 great importance because compounds had been decom- 

 posed previously only by heat, or by the action of some 



