172 ELEMENTARY LESSONS ON [CHAP. in. 



where the current entered the liquid, and hydrogen 

 bubbles where it left the liquid. It was soon found that 

 a great many other liquids, particularly dilute acids and 

 solutions of metallic salts, could be similarly decomposed 

 by passing a current through them. 



207. Electrolysis. To this process of decomposing 

 a liquid by means of an electric current Faraday gave 

 the name of electrolysis (i.e. electric analysis) ; and 

 those substances which are capable of being thus decom- 

 posed or " electrolysed " he termed electrolytes. 



The ends of the wires leading from and to the battery 

 are called electrodes ; and to distinguish them, that by 

 which the current enters is called the anode, that by 

 which it leaves the kathode. The vessel in which a 

 liquid is placed for electrolysis is termed an electrolytic cell. 



208. Electrolysis of "Water. Returning to the 

 decomposition of water, we may remark that perfectly 

 pure water appears not to conduct, but its resistance is 

 greatly reduced by the addition of a few drops of sul- 

 phuric or of hydrochloric acid. The apparatus shown in 

 Fig. 92 is suitable for this purpose. Here a battery of 

 two cells (those shown are circular Bun sen's batteries) 

 is seen with its poles connected to two strips of metallic 

 platinum as electrodes, which project up into a vessel con- 

 taining the acidulated water. Two tubes closed at one 

 end, which have been previously filled with water and 

 inverted, receive the gases evolved at the electrodes. 

 Platinum is preferred to other metals such as copper or 

 iron for electrodes, since it is less oxidisable and resists 

 every acid. It is found that there is almost exactly 

 twice as much hydrogen gas (by volume) evolved at the 

 kathode as there is of oxygen at the anode. This fact 

 corresponds with the known chemical composition of 

 water, which is produced by combining together these 

 two gases in the proportion of two volumes of the 

 former to one of the latter. The proportions of gases 

 evolved, however, are not exactly two to one, for at first a 



