"284 Mr. W. C. D. AYbethain on the 



the thermodynamic deduction of the gaseous value of the 

 osmotic pressure ceases to he valid. Unless we know at 

 what concentration this intersection begins to produce appre- 

 ciable effects, and what its result will be both on the 

 electrical and on the osmotic properties, we cannot infer that 

 the decrease in equivalent conductivity will proceed in 

 accordance with the decrease in the abnormal excess of 

 osmotic pressure. 



It has commonly been assumed, as a necessary consequence 

 of the dissociation theory, that the number of ions indicated 

 by the electrical conductivity must agree with the number of 

 particles producing osmotic pressure both at extreme dilution, 

 when the ionization is usually complete, and also when the 

 concentration is increased to a moderate extent and some of 

 the ions recombine. While it seems likely that the first of 

 these relations should hold in cases where the ionization is 

 known to be complete, it will now be evident that the second 

 relation can only exist if the connexion between the ions, 

 which is produced by increasing the concentration, affects 

 equally both the conductivity and the osmotic properties* 

 ^uch might be the case were the only result of increasing- 

 concentration to cause a certain number of ionic re-combi- 

 nations to form electrically inactive molecules, each molecule 

 producing the normal osmotic effect; but. if any other appre- 

 ciable influence arises from ion to ion, it may possibly change 

 the rate of variation of available energy with dilution, that 

 is. the osmotic pressure, before it decreases the ionic mobility. 

 The second relation then can only be expected to hold while 

 the solute particles are beyond each other's sphere of action, 

 and the experimental examination of the relation merely 

 gives a means of estimating at what dilution this condition 

 fails. The conductivity shows that ionization begins to be 

 incomplete at very great dilutions. Even for monovalent 

 salts, such as potassium chloride, the equivalent conductivity 

 begins to diminish at concentrations of about 10 -3 gram- 

 equivalent per litre, while, with salts containing divalent 

 ions, it is doubtful if complete ionization is more than just 

 reached at the greatest dilution which can be investigated 

 experimentally, namely about 10 -5 gram-equivalent per litre. 

 Incomplete ionization, however, does not necessarily connote 

 inter-ionic influences except at the moments of collision and 

 in the combined molecules, while for non-electrolytes, the 

 gaseous value of the osmotic pressure is known to extend to 

 much higher concentrations. It is possible, therefore, that 

 the second relation suggested by the theory should hold good 

 for a certain small range of concentration. Nevertheless, as 



