ELECTROLYTIC DISSOCIATION 63 



accumulated in support of this view will only be partly 

 mentioned here. In the Third Part of these lectures, in 

 which the relations between constitution and properties 

 are to be discussed, many opportunities will arise to draw 

 qualitative and quantitative conclusions from the idea of 

 Arrhenius, as was the case in the First Part (p. 117), in 

 dealing with the conditions of equilibrium in electrolytes. 

 Here we are specially concerned with the question, on 

 which the decisive proof turns, whether the degree of 

 decomposition deduced from the theory of solutions agrees 

 with that arrived at independently on the basis of the 

 electrolytic dissociation theory. 



The form in which the departure of electrolytes from 

 Avogadro's law, as applied to solutions, is to be given, may 

 conveniently follow on the so-called isotonic coefficients 

 introduced by de Vries (p. 38) ; these give how many 

 times more effective a molecule of salt in an isotonic 

 solution is, with regard to plasmolytic or osmotic action, 

 than a sugar molecule, the latter being, for special reasons, 

 taken as = 2. We have modified this mode of expression 

 by taking sugar and other substances following Avogadro's 

 law as unity, and writing the halved isotonic coefficients 

 so arrived at with the letter t. If then, for a certain con- 

 centration, i = 1-75 for nitre, that means that if each molecule 

 of nitre were replaced by 1-75 molecules of sugar, a solution 

 isotonic with that of nitre would be obtained. Hence the 

 osmotic pressure of the nitre solution is 1-75 times the 

 normal amount, so that the quantity t may also be 

 obtained as the ratio between the molecular depression 

 of the freezing point t proportional to the osmotic pressure, 

 and the normal value i8'5 found for sugar and other 

 non-electrolytes, or 



For the same temperature and concentration, the same 

 value of t should be obtained, whichever of the methods 



