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SCIENCE PROGRESS. 



ference in the behaviour of different solvents. Nernst has 

 recently (1894) put forward the view that differences in 

 the values of the dielectric constants of the solvents are an 

 important factor. This idea is based on the fact that 

 the electrical energy of a system of charged conductors is 

 diminished on transferring it from one medium to another 

 having a higher dielectric constant. For this reason, as J. 

 J. Thomson first pointed out in 1893, if a molecule be re- 

 garded as composed of charged particles the forces in play 

 between them will be diminished in a medium having a 

 high dielectric constant, and the more readily, therefore, 

 will dissociation occur. Although, as will be evident later, 

 this reasoning can be directly applied to electrolytic solu- 

 tions, it is only by analogy that it can be used when dealing 

 with the action of a solvent on a molecular ao-oreo-ate. 

 Nevertheless, where the necessary facts are known, they 

 show that there is a close parallelism between the dis- 

 sociative action of solvents and their dielectric constants. 

 The following table ogives in order of magnitude the values 

 of the dielectric constants at 15 , determined by Landolt and 

 Jahn (1892), and by Thwing (1894), f° r tne liquids 

 commonly used as solvents. The positions of nitrobenzene 

 and acetie acid are somewhat exceptional, yet it is plain 

 that, in general, the solvents in which no association can be 

 detected belong to one end of the series, while hydrocarbon 

 solvents showing definite association fall at the other. 



