Chemistry and Physics. 387 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the verification of Dalton's law for Solutions. — It is well 

 known that Van't Hoff in 1886 first drew attention to the fact 

 that the equations representing the generalizations arrived at by 

 Boyle, Gay Lussac and Avogadro in the case of gases, are equally 

 applicable to dissolved substances if the osmotic pressure of the 

 molecules dissolved be substituted for the gaseous pressure. 

 Moreover he not only deduced these conclusions from thermody- 

 namic considerations, thereby giving them increased validity, but 

 he established a thermodynamic relation between the osmotic 

 pressure of a dissolved substance and the molecular lowering of 

 the vapor pressure, or that of the freezing point of the solution. 

 Wildeemann has now shown that the third gaseous law called 

 the law of Dalton also holds good for dilute solutions. Accord- 

 ing to Dalton's law the total pressure of a gaseous mixture in a 

 given space is equal to the sum of the partial pressures of the 

 constituents. In a solution of two or more substances it means 

 that the total osmotic pressure of two or more dissolved sub- 

 stances is the sum of the partial osmotic pressures of each of 

 them. Hence from the connection between osmotic pressure and 

 the depression of the freezing point it follows that the total 

 freezing point depression is equal to the sum of the partial freez- 

 ing point depressions of each of the dissolved substances. In his 

 experiments the author employed the freezing point method on 

 account of the readiness with which mixtures of substances can 

 be examined by means of it. The direct experimental proof of 

 the law consisted in verifying one of the thermodynamical gen- 

 eralizations with which it has been experimentally connected 

 The thermometers used read, the one to 0-001° and the other to 

 0-01°. After the freezing point of the water itself had been 

 determined, a certain quantity of a given non-electrolyte, urea 

 for example, was dissolved in it and the freezing point again 

 determined. The second non-electrolyte was then added and the 

 total depression noted which was produced by both electrolytes. 

 The substances used with the urea were resorcinol, cane sugar, dex- 

 trose and alcohol. The results are given in tabular form and 

 show that the constant of depression obtained for the second 

 electrolyte is in no way inferior to that obtained when it is dig- 

 solved by itself in water. This result proves that the depression 

 produced by the first electrolyte was calculated under a correct 

 assumption, i. e. that the freezing point depression produced by 

 the first electrolyte is independent of the presence of other sub- 

 stances in the liquid. 



In a second paper, Wildermann gives the results of experi- 

 ments made to verify the constant of Van't HofF for very dilute 

 solutions. This constant, i. e., the molecular depression of the 



