October 2, 1896.] 



SCIENCE. 



465 



oult's^ work attracted the attention of Vic- 

 tor Meyer, who made use of his methods in 

 the study of certain stereomeric bodies upon 

 which he was at work. And it is in con- 

 nection with stereoisomerism that the new 

 methods of determining molecular weights 

 have, perhaps, been of the greatest practical 

 value in the development of chemical 

 science ; for, without the positive proof that 

 the bodies studied are metameric and not 

 polymeric, the foundation for the belief that 

 they are stereomeric would be comparatively 

 weak. 



It is probably through articles published 

 by Victor Meyer ^'^ and Auwers " that cryo- 

 scopic methods for the determination of 

 molecular weights were first brought to the 

 attention of a wide circle of chemists. 

 Since then a large number of workers have 

 busied themselves with the subject, partly 

 in the development of suitable forms of ap- 

 paratus and methods of manipulation, 

 partly in the study of the scope and degree 

 of accuracy of the laws and of exceptions to 

 them. The most important of the methods 

 developed are those dependent on the lower- 

 ing of the freezing point of solutions,^^ on the 

 raising of the boiling point.^^ on the lower- 

 ing of the vapor pressure,^* on the deter- 

 mination of isotonic solutions by vegetable 

 membranes ^^ and by blood corpuscles, and 

 on the lessening of the solubility of ether in 

 water or of phenol in water by the addition 

 of substances soluble in ether or phenol but 

 not in water. In the last case the determi- 

 nation is either direct in the case of phenol, 

 or by the rise of the freezing point of the 

 water ^® owing to the withdrawal of ether 

 from it. 



As was to be expected, the laws of osmot- 

 ic pressure are subject to numerous excep- 

 tions, or rather modifications, for, strictly 

 speaking, no true law of nature is ever sub- 

 ject to an exception. That which, by a 

 figure of speech, we call an exception is 

 really a modification due to the simultane- 



ous application of some other law. The 

 modifications in this case are very similar to 

 the modifications of Avogadro's law, which 

 retarded its acceptance for nearly a half 

 century. Vapor densities are abnormally 

 high on account of the associative tendency 

 of molecules, as in the case of acetic acid, or 

 when too near the boiling point of the liquid, 

 or low on account of dissociation, as in the 

 case of ammonium chloride or of phosphorus 

 pentachloride. In a similar manner the 

 molecular weights of most acids when de- 

 termined in solution in benzene are twice 

 their normal value, while the molecular 

 weights of electrolytes dissolved in water, 

 and sometimes when dissolved in other 

 solvents, are less than we should expect. 

 In addition to the modifications of the law 

 due to association and dissociation are other 

 modifications similar to the modification of 

 the laws of Boyle and Charles for gases 

 which are highly compressed. These 

 cases have been studied and formulae for 

 the deviation, based on the formulae of van 

 der Waals for compressed gases, have been 

 given by Ostwald, Bredig and A. A. ISToyes." 

 These formulae give a satisfactory expres- 

 sion for the deviation in many cases of con- 

 centrated solutions. When we consider 

 that strong solutions often give osmotic 

 pressures of many atmospheres, and that 

 the molecules of the bodies in solution are 

 often much more complex than the mole- 

 cules of most gases, it is readily seen that 

 deviations of considerable amount may be 

 expected. 



In 1884 Arrheneus^^ published the results 

 of researches on the electrical conductivity 

 of solutions, on which he had been engaged 

 for two years. In the course of his studies 

 he was led to the conclusion that only a 

 part of the molecules of an electrolyte are 

 concerned in conveying the electrical cur- 

 rent, and that it is necessary to distinguish 

 between '■ active ' and ' inactive ' molecules 

 in this regard. The conductivity is greater, 



