xiii CHEMICAL CHANGE BY ELECTRIC CURRENT 205 



electrolysis of copper sulphate. It accounts for the reddening of 

 the solution in the beaker and for the evolution of oxygen which 

 takes place at the anode. 



CHIEF POINTS OF CHAPTER XIII. 



The Galvanoscope is a convenient apparatus for recognising the 

 passage of an electric current. 



The Passage of the Electric Current through Liquids. 



(a) Liquid metals conduct the current without being decom- 

 posed. 



(b) Certain liquids, like turpentine, will not conduct the electric 

 current and are consequently not decomposed by it. 



(c) Compound liquids, which, like acidulated water, conduct the 

 electric current, are decomposed by its passage. 



Electrolysis is the term used to refer to condition (c) above. It 

 means the process by which electric currents pass through compound 

 liquids and so cause them to be decomposed. The liquid which 

 conducts the electric current and is itself decomposed is known as 

 the electrolyte. 



The ends of the wires coming from the poles of the battery are 

 called electrodes, that by which the current enters the electrolyte is 

 known as the anode, that by which it leaves the kathode (or cathode). 



The atoms into which the electrolyte is decomposed are called ions. 



The ions which collect at the anode are the anions ; those which 

 collect at the kathode the kathions (or cathions). 



Electrolysis of Water, HoO 



w Tin? i g decomposed by the HYDROGEN -, OXYGEN 

 " electric current into [2 vols.] ia [1 vol.] 

 a fact which can be at once simply expressed by chemical symbols : 

 H 2 O = H 2 + 0. 



Electrolysis of Copper Sulphate, CuS0 4 . First, the copper sul- 

 phate is broken up into copper and the group of elements S0 4 , 

 thus : 



Then a secondary reaction takes place between the group of 

 elements S0 4 , and the water in which the copper sulphate is 

 dissolved : 



The final result is that copper is deposited at the kathode and 

 bubbles of oxygen are evolved at the anode. 



Electrolysis of Sodium Sulphate, Na. 2 S0 4 . First, the sodium 

 sulphate is decomposed into sodium and the group of elements S0 4 , 

 thus : 



Na 2 S0 4 =Na 2 + S0 4 . 



This decomposition is followed by two secondary reactions : the 

 sodium at once acts upon the water present forming sodium hydrate 

 and evolving hydrogen : 



Na 2 4 2H 2 = 2NaOH + H 2 ; 



