CH. VII.] COMPOSITION OF PURE WATER. 



lOI 



out entering, however, into the famous " water controversy," 

 let us see what are the simplest means by which the 

 composition of so common a substance may be ascer- 

 tained. 



In these days of electric telegraphy every one is familiar 

 with the instrument known as the galvanic or voltaic battery. 



Fl6. 25. — Decomposition of water by electricity. 



In the year 1800, Messrs. Nicholson and Carlisle discovered 

 that, when a current of electricity from a galvanic battery is 

 sent through water, the liquid is at once spHt up into its 

 constituents. Fig. 25 represents an ingenious apparatus, 

 devised by Dr. Hofmann, for effecting this decomposition. 

 It consists of a U-shaped tube of glass, OH, connected 



