416 



SCIENCE PROGRESS. 



as compared with that of the vapour, and on assuming the 

 vapour to obey gaseous laws, it follows that — 



dpldt = MX//2T 2 (8) 

 where X is the heat of vaporisation in calories of 1 gram of 

 solvent at T, its boiling-point on the absolute scale. Sub- 

 stituting for dpldt in (7) on putting A = 1 we obtain— 



M' AT/g = -02T7X (9). 

 M'AT/^- is the molecular rise in the boiling-point, or the rise 

 which would be produced on dissolving a gram -molecule of 

 substance in 100 gr. of solvent if AT remained proportional 

 to^-, i.e., to the concentration. The equation indicates that 

 the molecular rise should be the same for all dissolved 

 substances and should depend solely upon the physical con- 

 stants of the solvent. 



The following examples taken from the extensive obser- 

 vations of Beckmann serve to illustrate the degree of ap- 

 proximation with which these deductions correspond with 

 the results of experiment. 



SOLUTIONS IN BENZENE. 



SOLUTIONS IN ALCOHOL. 



