ELETCIIOLYTIC SOLUTIONS 31 



potassium bromide and sodium bromide. Hence we may con- 

 clude that the conductivity of any salt is an ionic property. 



Kohlrausclfs law may be expressed by the formula c = 

 <l(ii -{-!■), where c is the conductivity of the salt, d the degree 

 of dissociation, i.e. the fraction of the electrolyte broken up 

 into ions, and u and v the velocity of the anions and cations 

 respectively. When all the molecules of the electrolyte are 

 dissociated, d=\, and the formula becomes c r =u-\-v. 



As we have already seen, a salt is formed by the union of 

 a metal M with an acid radical R. Potassium sulphate, K 2 S0 4 , 

 consists of the metal K 2 and the acid radical S0 4 . Ammonium 

 chloride, NII 4 ('l, consists of the basic radical NII 4 and the 

 acid radical CI. The various acids may be considered as salts 

 of the metal hydrogen. Thus sulphuric acid, II 2 S0 4 , is the 

 sulphate of hydrogen. Rases may be considered as salts 

 with the hydroxyl group, OH, replacing the acid radical. 

 Thus potash, KOH. is the hydroxyl of potassium. The various 

 electrolytic combinations may be represented by the following 

 symbols : — 



Salts = MR. 

 Acids = HR. 

 Rases = MOH. 



The various chemical reactions of an electrolyte are all 

 ionic reactions, the chemical activity of an electrolytic solution 

 being proportional to its electric conductivity, i.e. the degree 

 of dissociation of its ions. The acidity of an electrolytic 



+ 

 solution is due to the presence of the dissociated ion H, and 



its strength is determined by the concentration of these free 



hydrogen ions. Hence the greater the degree of dissociation 



the stronger the acid. 



The basic character of a solution is determined by the 



presence of the hydroxyl radical OH. The greater the con- 

 centration of the hydroxyl ions, i.e. the greater the dissociation, 

 the stronger is the base. 



The ions H and OH are of special importance, since they 

 are the ions of water, 1 1.,0 = II + OH. The degree of dissocia- 



