VOLUME CHANGES IN THE PROCESS OF SOLUTION. 81 



traction in the volume of the water, and also that although 

 the actual volume of the latter in both cases is less than 



—— it is sensibly the same in both solutions. 

 do 



In calculating the specific solution volumes of these solu- 

 tions according to Equation T, it follows that in both cases 

 v s would be less than the actual volume occupied by one 

 grain of the solute in the solution, and furthermore, the 

 error so obtained would decrease with increasing values of 

 A. Even in a case where the actual specific volume of the 

 solute was constant and independent of its concentration, 

 the values found for v s would increase with A. We cannot 

 infer, therefore, that because the values of v s are found to 

 vary in a definite direction with concentration, the actual 

 specific volume of the solute varies in this direction, or 

 indeed that there is any variation at all. This particular 

 point can be well illustrated by considering a solution 

 formed by mixing two liquids, e.g., formamide and water, 

 in which the formamide is considered the solute and the 

 water the solvent. The formamide used in these experi- 

 ments was purified by the method of Kohler, J by standing 

 over anhydrous sodium sulphate from which it was distilled 

 under reduced pressure. The density of the pure amide at 

 25° C. was 1'13126. The densities of the solutions were 

 determined both at 20° C. and 25° C. and the specific solu- 

 tion volume of the formamide in water calculated in the 

 usual way. In addition, the contraction per cc, of the 

 original volume was determined by subtracting the volume 

 of the solution from the sum of the volumes of the con- 

 stituents, and dividing this difference by the original 

 volume of the constituents. Thus if x represents the 

 volume of formamide, y the volume of water, and z the 

 resulting volume of the solution, then the specific contrac- 

 tion Av is given by: 



1 Zeit. f. Electrochem., 16, 420. 

 F— August 6, 1919. 



