3 88 



POPULAR SCIENCE MONTHLY. 



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can take place. This represents the Grotthuss scheme, that supposes 

 continuous decompositions and recombinations of the salt molecules. 

 As such exchanges of ions between the molecules take place even 

 under the influence of the weakest electromotive forces, Clausius con- 

 cluded that they must also take 

 •A- B place if there is no electric force, 



i. e., no current at all. In favor 

 of his hypothesis he pointed to 

 the fact that Williamson, as far 

 back as 1852, in his epoch- 

 making theory of the formation 

 of ethers, assumed an analogous 

 exchange of the constituents of 

 the molecules. At this exchange 

 of ions it might sometimes, 

 though extremely rarely, happen 

 that an ion becomes free in the 

 solution for a short time; at 

 least such a conception would be in good agreement with the mechan- 

 ical theory of heat, as it was developed by Kronig, Maxwell, Clausius 

 and others at that time. 



In the meantime, Bouty, and particularly Kohlrausch, worked out 

 the methods of determining the electric conductivity of salt solutions. 

 In 1884 I published a memoir on this subject. I had found that if 

 one dilutes a solution — e. g., of zinc sulphate — its conductivity per 

 molecule, or what is called its molecular conductivity, increases not 

 infinitely, but only to a certain 

 limit. We may figure to ourselves 

 an experiment performed in the 

 following manner (Fig. 3) : In a 

 trough with parallel walls there are 

 placed close to two opposite sides 

 two plates of amalgamated zinc, 

 E E x . On the horizontal bottom 

 of the vessel there is placed a layer 

 of solution of zinc-sulphate that 

 reaches the level 1. The conduc- 

 tivity may be fc 1 . After this has 

 been measured we pour in so much 

 water, that after stirring the solu- 

 tion the level reaches 2, which lies as much above 1 as this lies above 

 the bottom. The conductivity is then found to be increased, and to 

 have the value k 2 . Increasing in the same manner the volume by addi- 

 tion of pure water until it is doubled, the level 4 is reached and the 



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Fig. 3. 



