VOLUME CHANGES IN THE PROCESS OF SOLUTION. 97 



It will be seen from the above results that in every case 

 considered, the specific solution volume of a solute is 

 greater in a water-alcohol mixture than in either water or 

 alcohol, and not intermediate between its value in the 

 simple liquids. In the case of formamide as solute the 

 specific solution volume is actually greater than the specific 

 volume of the pure liquid, although the solution volume in 

 either water or alcohol is considerably less. In the ex- 

 amples where the solution volume has been determined in 

 a series of water-alcohol mixtures, a more or less definite 

 maximum has been found, but the position of the maximum 

 varies with the solute. The maximum solution volume of 

 carbamide is found in a solution containing about 32 per 

 cent, of alcohol both at 25° and 30° 0., but in the case of 

 both acetamide and sucrose, the mixture corresponding to 

 the maximum contains over 40 per cent, of alcohol. 



Maxima or minima have been recorded for several 

 physical properties of alcohol-water mixtures, but the 

 position of such maxima are by no means constant. These 

 abrupt changes in the physical properties of mixtures have 

 been interpreted by various authors as indicating combina- 

 tion between the alcohol and water with the formation of 

 more or less stable "solvates." If this be so, the results 

 obtained for solution volumes of solutes in such mixtures 

 indicate in addition, the existence in the solution of sol- 

 vates between the solute and either water or alcohol or 

 both. The formation of a solvate results in a change in 

 the specific volume, the magnitude of which will vary with 

 the particular solvate in question. Combination between 

 the alcohol and water molecules results in a contraction 

 in volume, which varies with the composition of the mixture 

 and also the temperature. If in such a mixture we dissolve 

 a solute, which also forms a solvate with water (or 

 alcohol) the original equilibrium of the system will be 



G— August 6, 1919. 



