CHAP, in.] ELECTRICITY AND MAGNETISM. 



173 



very small quantity of the hydrogen is absorbed or 

 " occluded " by the platinum surface, while a more con- 

 siderable proportion of the oxygen about I per cent 



Fig. 92. 



is given off in the denser allotropic form of ozone, which 

 occupies less space and is also slightly soluble in the 

 water. When a sufficient amount of the gases has been 

 evolved and collected they may be tested ; the hydrogen 

 by showing that it will burn, the oxygen by its causing 

 a glowing spark on the end of a splinter of wood to burst 

 into flame. If the two gases are collected together in a 

 common receiver, the mixed gas will be found to possess 

 the well known explosive property of mixed hydrogen 

 and oxygen gases. The chemical decomposition is ex- 

 pressed in the following equation : 



H 2 H 2 +0 



Water yields 2 vols. of Hydrogen and i vol. of Oxygen. 



2O9. Electrolysis of Sulphate of Copper. We 



will take as another case the electrolysis of a solution of 

 the well-known " blue vitriol " or sulphate of copper. If 



