14 THE THEORY OF IONS 



are liquids which do not conduct electricity or only 

 do so with difficulty because they do not become 

 ionised ; e.g. pure water, aqueous solutions of 

 alcohol or sugar, benzene, and a large number of 

 organic compounds which do not fall under the head 

 of salts, acids or bases.. Electrolytes are readily 

 ionised and good conductors of electricity, e.g. 

 aqueous solution of chloride of sodium or of strong 

 acids, strong bases and nearly all salts. There are 

 materials which stand between the two called Half- 

 electrolytes, including weak acids, e.g. tartaric, 

 acetic and oxalic acids ; the weak bases, e.g. 

 ammonium hydroxide, and hydroxides^ of metals 

 other than alkaline earths. 



Dissociation takes place in chemicals having 



(a) a homogeneous system, like ammonium chloride, 

 ammonium sulphide, mercurous chloride, phos- 

 phorous pentachloride or amylene chloride ; and 



(b) in systems that are not homogeneous, as the 

 hydrated salts, the carbonates of lime, magnesia 

 and silver, the oxides of mercury and iridium, com- 

 pounds of the metallic oxides and metallic hydrides.* 

 Ions are produced in many ways, both in liquids and 

 gases. When a gas is traversed by uranium rays 

 ions are produced which are charged with electricity, 

 and the same effect follows the action of cathode 

 rays.f The ionisation is independent of the com- 

 position of the gas, and varies directly as the pressure 

 and density.} 



Some salts are more or less decomposed by water, 



* Watts' "Diet. Chern. ": article, "Dissociation." 

 I McLennan: Proc. Roy. Soc., 1900, Ixvi., 375. 

 Ibid. 



