ASSOCIATION AND DISSOCIATION. 183 



apply when the solvent is associating. The probability- 

 is that some suitable modification is required and the 

 introduction of a factor due to the associating character 

 of the solvent. 



It can be shown that, if the influence which the associa- 

 tion of the solvent is here supposed to exercise on the 

 osmotic pressure be admitted, the osmotic pressure of a 

 solution containing an associating solvent should always be 

 greater than that of a solution of similar concentration with 

 a monomolecular solvent. Solutions of Class II. might 

 therefore be expected to exhibit osmotic pressures that 

 would approximate to the normal calculated values, and 

 solutions of Class IV. would have osmotic pressures greater 

 than the normal. It fact solutions of Class IV. would 

 possess the behaviour met with among electrolytes, and as 

 shown above electrolytes do in all probability belong to this 

 class of solutions. 



The supporters of the theory of electrolytic dissociation 

 deny that the character of the solvent can have any direct 

 influence on the osmotic pressure of a solution. The 

 thermo-dynamical treatment of the subject leads to this 

 conclusion, and any contrary view argues a flaw in the 

 train of reasoning by means of which this result has been 

 obtained. The difficulties that arise in applying thermo- 

 dynamics to chemical investigations have been well illustrated 

 by Fitzgerald in his Helmholtz Memorial Lecture. And 

 a difficulty which has been overlooked occurs in dealing 

 with dilute solutions. A monomolecular solvent does not 

 change in composition with rise or fall of temperature, but 

 any change in temperature at^ once alters the composition 

 of an associating solvent. As temperature enters as one 

 of the factors into thermo-dynamical equations, in the 

 treatment of dilute solutions some distinction should be 

 drawn between those which contain monomolecular and 

 those which contain associating solvents. But up to the 

 present no such distinction has been made and all liquids 

 have been treated as exactly alike. 



In opposing to the theory of electrolytic dissociation the 

 view that association of the solvent influences the osmotic 



