Chap. V-] 



ELECTROLYSIS. 



5 1 



is liberated at the positive pole, and hydrogen at the 

 negative. The apparatus figured in Pig. 27, called a 

 voltameter, is employed for showing this decomposi- 

 tion. It consists of two tubes filled with water. 

 The tubes are inverted in a vessel, also containing 

 water, over strips of platinum. The strips are con- 

 nected by wires to binding screws, to which the 

 positive and negative wires of a battery are attached. 



Fig. 27. The Voltameter, 



The liberated gases rise from the strips, and are 

 collected in the tubes. The tube connected with the 

 negative pole has twice as much gas (hydrogen) as 

 that connected with the positive. Thus one obtains 

 not only a qualitative but also a quantitative analysis. 

 Pure water is not employed, because it is a bad 

 conductor. The water must be acidulated, usually 

 with sulphuric acid, and, of course, it may be really 

 only the acid that is decomposed. Other solutions 

 subjected to the passage of a current show similar 

 results, different elements appearing at different 

 electrodes. Salts may be decomposed by the current, 

 the acid appearing at the positive, and the base at 



