174 ELEMENTARY LESSONS ON [CHAP. in. 



a few crystals of this substance are dissolved in water 

 a blue liquid is obtained, which is easily electrolysed 

 between two electrodes of platinum foil, by the current 

 from a single cell of any ordinary battery. The chemical 

 formula for sulphate of copper is CuSO 4 . The result of 

 ; the electrolysis is to split it up into metallic copper, 

 which is deposited in a film upon the kathode, and 

 " Sulphion " an easily decomposed compound of sulphur 

 and oxygen, which is immediately acted upon by the 

 water forming sulphuric acid and oxygen. This oxygen 

 is liberated in bubbles at the anode. The chemical 

 changes are thus expressed : 



CuSO 4 Cu + SO 4 



Sulphate of Copper becomes Copper and Sulphion ; 



SO 4 + H 2 O H 2 SO 4 + O 



Sulphion and water produce Sulphuric acid and Oxygen. 



In this way, as the current continues to flow, copper is 

 continually withdrawn from the liquid and deposited on 

 the kathode, and the liquid gets more and more acid. If 

 copper electrodes are used, instead of platinum, no oxygen 

 is given off at the anode, but the copper anode itself dis- 

 solves away into the liquid at exactly the same rate as 

 the copper of the liquid is deposited on the kathode. 



21O. Anions and Kathions. "The atoms which 

 thus are severed from one another and carried invisibly 

 by the current to the electrodes, and there deposited, 

 are obviously of two classes : one set go to the anode, 

 the other to the kathode. Faraday gave the name of 

 ions to these wandering atoms ; those going to the 

 anode being anions, and those going to the kathode 

 being kathions. Anions are sometimes regarded as 

 " electro-negative " because they move as if attracted 

 toward the + pole of the battery, while the kathions 

 are regarded as " electro-positive." Hydrogen and the 

 metals are kathions, moving apparently with the direction 

 assumed as that of the current, and are deposited where 



