THE NEW THEORY OE SOLUTIONS. 



379 



shown in the following table based upon observations made 

 by Roth ( 1 880) on ethylene and carbon dioxide. P is the 

 pressure of the gas in atmospheres, g its concentration in 

 grs. per 100 cc, and M" the molecular weight. 



The values of M" are calculated on the assumption that 

 the gas obeys the ideal laws, and, according to the 

 kinetic theory, these laws apply only to gases in which the 

 attractive forces in play between the molecules are in- 

 appreciable, and for which the actual volume of the mole- 

 cules may be neglected in comparison with the volume of 

 the gas. To these disturbing influences, which must of 

 course become more and more important as the pressure 

 increases, .are ascribed the variation in the values of M", 

 and van der Waals' corrected gas equation, which takes 

 note of these influences, approximately expresses the be- 

 haviour of compressed gases. 



Theory of concentrated solutions. — Although the theory 

 of concentrated solutions cannot yet be adequately tested 

 experimentally, it is of service in explaining some of the 

 foregoing facts. By reasoning similar to that used by van der 

 Waals for gases, it follows that, owing to the attraction of 

 dissolved molecules for each other, the osmotic pressure of 

 a dissolved substance will be less than what it would other- 

 wise be by an amount proportional to the square of the 

 concentration. Acting in the opposite sense to this attrac- 

 tion will be the attraction between dissolved and solvent 

 molecules. The latter attraction will increase the osmotic 

 pressure by an amount which according to Arrhenius (1892) 

 is also proportional to the square of the concentration. This 



