PROGRESS IN PHYSICAL CHEMISTRY 



DURING 1894. 



Part II. 



MIXTURES. 



/ IQUIDS. — In connection with the physical properties 

 of mixed liquids, Ramsay and Aston (73) have 

 determined the surface tension of four binary mixtures of 

 non-associated liquids. In the case of mixtures of toluene 

 with piperidine, and benzene with carbon tetrachloride, the 

 surface tension and the molecular surface energy are 

 practically the mean of those of the constituents. The 

 simple admixture rule is not obeyed, however, by mixtures 

 of chlorobenzene with ethylene dibromide, and carbon 

 bisulphide with chloroform. From the rate of change 

 of the molecular surface energy, the authors infer that in 

 all cases, but the last, no change in the molecular aggrega- 

 tion of the liquids is produced by admixture. 



As another means of obtaining evidence regarding 

 change in molecular complexity produced by admixture, 

 Paterno and Montemartini (74) determine the densities of 

 mixtures of benzene with liquids which, from freezing-point 

 observations, have abnormally high molecular weights when 

 dissolved in benzene. They find that on adding one of the 

 lower fatty alcohols or acetic acid to benzene expansion 

 occurs. This, they consider, is an indication of disgregation, 

 and, therefore, of the existence of molecular aggregates in 

 the liquids. On the other hand, according to surface- 

 energy measurements, although chlorobenzene and ethylene 

 dibromide expand on admixture there is no molecular 

 aggregation. Indeed, that density observations are not 

 well suited for the end in view is shown by the fact that 

 the authors find that benzyl alcohol and butyric acid, which 

 have high molecular weights so far as freezing-point 

 observations go, exhibit contraction when added to 

 benzene. 



