An application to electrolytes of the hydrate theory of solutions / by T. Martin Lowry.

  • Lowry, T. Martin (Thomas Martin), 1874-1936.
Date:
[1905]
Catalogue details

Licence: In copyright

Credit: An application to electrolytes of the hydrate theory of solutions / by T. Martin Lowry. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    VIII. The results obtained by studying the freezing-points are compli- cated by the fact that both molecules and ions may enter into combination with the solvent. It may, however, be noted that the abnormality decreases in the series Li, Na, K, Rb, Cs, indicating that the hydration reaches a maximum in the case of lithium and decreases as the molecular weight increases. This result is confirmatory of the conclusions arrived at from a study of the ionic mobilities of the series. Collateral evidence is also afforded by the data for the molecular elevation of the boiling-point and the molecular lowering of the vapour pressure, which, likewise, exhibit minimum values.* Indications analogous to those resulting from a study of the freezing- points of aqueous salt solutions are afforded by the determination of the influence of dissolved salts on the solubility in water of neutral solids and gases. But, whilst the results are of considerable interest, the phenomena are too complex to permit of exact deductions as to the nature of the hydrates present in solution. IX. Extension of the theory to fused salts. Autolytic and heterolytic conductivity. Whilst the hydrate theory of ionisation applies primarily to aqueous electrolytes, it can be used, without any substantial alteration, in all cases of heterolytic conductivity in which the electrolytic properties of a solution are due to the interaction of the solute with an ionising solvent. Thus in non-aqueous solutions it is probable that complexes are formed in which molecules of ammonia, sulphur dioxide, etc., plays the same part as the water in the hydrates referred to in the preceding part of the paper. Ionisa- tion may therefore again be attributed to the superior combining power of the ions as compared with the molecules of the dissolved salt. Some slight modification of the theory is necessary to render it applicable to the case of autolytes which become conductors when merely fused. No method is at present known of determining the coefficient of ionisation of fused salts, and Whethamf has pointed out that it is possible in this case to apply the old Grotthus theory of electrolysis, according to which free ions do not exist in the liquid, and the coefficient of ionisation is therefore zero. Various reasons may, however, be urged in favour of the view that the mechanism of electrolysis is similar to that which obtains in solution, and that only a part of the fused salt is directly active in electrolysis. Thus :— (1) Polymerisation appears to be an essential characteristic of autolytic salts. Volatile compounds and compounds which are liquids at ordinary temperatures, and are therefore but slightly associated, are usually insulators except when associated with an ionising solvent. The acids are therefore heterolytes, whilst the salts derived from them are autolytes. Again, stannic chloride is in an insulator, whilst stannous chloride is a conductor when fused. Mercuric chloride is a poor conductor, but the silver haloids, which are insoluble and non-volatile, though readily fused, conduct even better than such liquids as 30 per cent, sulphuric acid, which exhibit the maximum conductivity obtainable in composite electrolytes {see Armstrong, Proc. Royal Soc., 1886, 40, 280). (2) Definite proof of the polymerised character of fused salts has been obtained by J. F. Bottomley {Trans. Client. Soc., 1903, 83, 1421-1425), who has found the coefficients of association of sodium and potassium nitrates, as determined from measurements of surface tension, to be io’68 and 873 respectively. He concludes that “the conductivity of fused salts is to be * A. Smits, Zeitsclir. Phys. Client., 1902, 39, pp. 385-432. f Prpc. Far. Soc., June 30, 1903.