THEIR FORMATION 13 



are charged with electricity and are called ions ; 

 they travel through the water to the electrodes 

 where they discharge their electricity ; the hydrogen 

 conveying positive electricity to the cathode, and 

 the oxygen conveying negative electricity to the 

 anode, where they escape. Many substances may 

 be dissociated into ions by electricity, e.g. hydro- 

 chloric acid, ammonia, carbonic acid, acetylene, 

 and ozone is formed from oxygen of the air, ions being 

 formed in each case. 



All substances cannot be ionised, nor are all 

 substances conductors of electricity. If the two 

 poles of a Battery are connected by a bar of graphite 

 the current readily passes ; but if they are connected 

 by sulphur no current will pass. Conductors of 

 electricity are of two kinds ; those which become 

 heated, including all metals and some non-metals, 

 and those which undergo a chemical change during 

 conduction. The latter include a very large number 

 of compound substances in a liquid state or in some 

 solvent. Pure water is a non-conductor,, and when 

 the poles of a battery are inserted into it no current 

 passes ; but if some hydrochloric or other acid is 

 added the solution becomes a conductor and a cur- 

 rent passes ; at the same time hydrogen and chlorine 

 are disengaged at the cathode and anode respectively, 

 i.e. the acid becomes dissociated into ions charged 

 with electricity which they convey to the electrodes 

 they are electrolysed and the liquid is called an 

 electrolyte. It is the substance in the liquid which 

 is really the electrolyte and which becomes ionised ; 

 it is usually understood to be in solution in water. 

 Liquids are classified as follows :* Non-electrolytes 



* Newth's " Inorganic Chemistry," tenth edition, p. 97. 



