CHATTER III 



ELECTROLYTIC SOLUTIONS 



Solutions -which conduct Electricity. — The laws of solution 

 which we have studied in the previous chapter apply only to 

 those solutions, chiefly of organic origin, which do not conduit 

 electricity. Solutions of electrolytes such as the ordinary 

 salts, acids, and bases, which are ionized on solution, give values 

 for the various constants of solution which do not accord with 

 those required by theory. If, for instance, we take a gramme- 

 molecule of an electrolyte such as chloride of sodium, and 

 dissolve it in a litre of water, we find that the lowering of the 

 freezing point is nearly double the theoretical value of 1*85 . 

 The same holds good for the osmotic pressure, and for all the 

 constants which are proportional to the molecular concentra- 

 tion of the solute. The solution behaves, in each case, as if it 

 contained more than one gramme-molecule of sodium chloride 

 per litre. It behaves, in fact, as if it contained i times the 

 number of molecules of solute originally introduced into it. 

 If n be the original number of molecules, then it will apparently 

 contain n' = in molecules. This law is universal for all 

 electrolytic solutions; the theoretical value for their concen- 

 tration, osmotic pressure, and all the proportional physical 



constants must be multiplied by this quantity, /'= -, which is 



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the ratio of the apparent number of the molecules present 



to the number originally introduced. 



A similar dissociation of the molecule is observed in the 



case of many gases. The vapour of chloride of ammonium, 



for instance, is decomposed by heat, and it mav he shown 



experimentally that the increase of pressure on heating above 



