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Page:Popular Science Monthly Volume 65.djvu/393

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389
ELECTROLYTIC DISSOCIATION.

conductivity is found to be greater than in the previous case—say k4. So we may proceed further and further; the conductivity increases, but at the end more slowly than at the beginning. We approach to a final value k8. This is best seen in the next diagrams, which represent the newer determinations of Kohlrausch (Figs. 4, 5).

PSM V65 D393 Molecular conductivity speed chart.png
Fig. 4. Fig. 5.

I explained this experiment in the following manner: The conductivity depends upon the velocity with which the ions (Zn and SO4) of the molecules (ZnSo4) are carried through the liquid by the electric force, i. e., the potential difference between E and E1. If this potential difference remains constant, the velocity depends only on the friction that the ions in their passage through the liquid exert on the surrounding molecules. As these, at higher dilutions, are only water molecules, it might be expected that the conductivity would remain constant and independent of the dilution if it be supposed that all molecules, ZnSO4, take part in the electric transport. As experiment now teaches us that the molecular conductivity increases with the dilution, even if this is very high (1,000 or more molecules of water to one molecule of ZnSO4), we are led to the hypothesis that not all, but only a part of, the ZnSO4 molecules take part in the transport of electricity. This part increases with the dilution in the same proportion as the molecular conductivity k. The limiting value k8 is approached at infinite dilution, and corresponds to the limit that all molecules conduct electricity. The conducting part of the molecules I called the active part. It may evidently be calculated as the quotient k:k8.

If now this new conception were only applicable to the explanation of the phenomena of electric conductivity, its value had not been so