THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 195 



For the liberation of carbon-dioxide gas the representation is this : 



Na 2 C0 3 ^ 2Na' + CO/ ' ) ^ rn 



H 2 S0 4 ^S0 4 " + 2H- /- H 2 C 3= H 2 + C0 2 (gas). 



I t 

 Na 2 SO 4 soluble. 



Or simply 



2Na- + CO/ ' + 2H- + SO/ ' = 2Na' + SO/ ' + H 2 CO 3 . 



Carbonic acid is only slightly ionized and very little soluble. Hence 

 it escapes as fast as it is liberated. This description will serve also 

 for the liberation of nitrous acid from nitrites. 

 The formation of nitric acid is represented thus : 



it 



K 2 SO 4 non-volatile. 



Or simply 



2K- + 2NO 3 ' + 2H- + SO/' = 2K- + SO/' + 2HNO 3 . 



As concentrated sulphuric acid and dry potassium nitrate are used in 

 this process, only a relatively small number of ions are present at one 

 time, but as fast as ions are removed as nitric acid, new ions are 

 formed to replace them until the operation is completed. 



The above discussions on the formation of precipitates, gases, and 

 volatile liquids, and consequent completion of chemical reactions, is a 

 presentation in terms of the ionic theory of the same subjects dis- 

 cussed in a simpler form on p. 114, under Reversible Actions and 

 Chemical Equilibrium, and furnish an explanation of what is there 

 stated. 



Chemical actions in aqueous solutions are nearly always actions 

 between ions. Indeed, there are some who claim that chemical action 

 does not take place except between ions, and the fact that action does 

 occur is itself evidence of the presence of ions. This is an extreme 

 view and is not well taken, as there are undoubted examples of action 

 in solution in which ions do not exist. In the case of acids, bases, 

 and salts in solution, action is practically always ionic. 



Electrolysis. 



This name is given to the series of changes that take place when an electric 

 current is passed through a solution of an electrolyte, and the subject is briefly 

 discussed on page 82. The process is carried out in an electrolytic cell, which 

 consists of a suitable vessel holding a solution into which are immersed the 

 electrodes of the circuit. Fig. 34 illustrates one form of such a cell, which 



