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IV. Electrolytic Dissociation versus Hydration. 



By SVANTE ArRHENIUS*. 



THE distinguished Russian chemist Mendelejeff has lately, 

 in the Journal of the Russian Physico-chemical Society, 

 dealt in an adverse manner with the theory of electrolytic 

 dissociation. In that paper he expresses an opinion that his 

 assumption of the existence of hydrates in solutions can be 

 used to explain all the facts which hitherto have served as the 

 foundation of the electrolytic-dissociation theory. As many 

 English chemists (Armstrong, Crompton, Pickering) have in 

 recent publications accepted and defended Mendelejeff 's views, 

 I take this opportunity of offering a few observations in an 

 English scientific journal on Mendelejeff 's paper. 



In his paper the Russian savant makes use only of the data 

 contained in the first memoir of van't Hoff (at the time of 

 publishing which the latter was not acquainted with the theory 

 of dissociation), and pays no attention to the later develop- 

 ments of the subject. Only in this way can Prof. Mendelejeff 's 

 concluding advice be explained, that before going further we 

 must investigate whether the isotonic coefficients (i) of van't 

 Hoff and de Vries are whole numbers or vary with the tem- 

 perature and concentration. I have proved more than a year 

 ago (Zeitschr. fur physikal. Chemie, ii. p. 491) that the latter 

 alternative is correct ; e. g. for oxalic acid the values of i 

 corresponding to the concentrations '06 and '66 gram- 

 molecules per litre are 1*62 and 1*37 respectively. This can 

 also be deduced from the electric conductivities of the solu- 

 tions. Moreover I know of no one who has refused to accept 

 this alternative. I refer, for example, to the more recent 

 papers in the Zeitschr .fur physikal. Chemie of de Yries and van't 

 Hoff, both of whom at first held the other view. The state- 

 ment that the isotonic coefficient of MgS0 4 at all concentra- 

 tions is unity must also be corrected in the same sense ; as I 

 have found that this coefficient has the values 1*37, 1*22, and 

 1*04 for the concentrations '06, '16, and '66 gram-molecules 

 per litre. Thus the question, " how is it that in this case i 

 for an electrolyte is unity?" is answered. Evidently by this 

 neglect of a great part of what has been accomplished by the 

 theory of dissociation Prof. Mendelejeff has come to the belief 

 that the whole matter may easily be explained in another way. 

 I therefore give an enumeration of the principal branches of 

 physical science which have received an explanation from the 

 hypotheses of osmotic pressure and of electrolytic dissociation. 

 * Communicated by the Author. 



