Theory of Electrolytic Dissociation. 287 



accurate determinations of freezing-points are those under- 

 taken by Dr. E. H. Griffiths by the methods of platinum 

 thermometry. The results as yet obtained were announced 

 to the British Association in the year 1901. From concen- 

 trations 0*0005 to 002 normal, the molecular lowering of 

 the freezing-point of water produced by cane-sugar was 

 found to be 1-858, while that produced by potassium chloride 

 slowly increased with the dilution, till, in a solution of 

 0*0003 gram-equivalent per litre, it reached 3*720. Thus 

 the non-electrolyte gave the theoretical result, and the binary 

 electrolyte twice the molecular depression of the non-electro- 

 lyte, within extraordinarily narrow limits of experimental 

 error. At this concentration the conductivity indicates that 

 the ionization is about 99*7 per cent. Thus the evidence at 

 present available goes to support the accuracy of the first 

 relation of Arrhenius' theory in the case of aqueous solu- 

 tions ; the observed depressions never appreciably exceed 

 the theoretical values, and the discrepancies in the other 

 direction are readily explicable by incomplete ionization. 



Passing to solutions in solvents other than water, we 

 find that sufficient data are not available to decide whether 

 the same relation between the electrical and the osmotic 

 phenomena holds good. The difficulties of experiment are 

 much increased, and no observations on osmotic effects seem 

 to have been made on solutions in which the dilution was 

 carried far enough to secure complete ionization. In many 

 aqueous solutions, such as those of acetic acid and ammonia, 

 complete ionization cannot be experimentally attained ; and. 

 without definite evidence, we cannot assume that it is in 

 general reached by possible dilution in another solvent. 

 For reasons already indicated, measurements on stronger 

 solutions are of little use in this connexion. Moreover, for 

 non-aqueous solutions we usually have little knowledge of 

 the general electrolytic behaviour, and of such electrical con- 

 stants as the transport numbers, so that it is not safe to 

 conclude that the ions are of the same nature as those of the 

 corresponding solutions in water. In alcoholic solutions, at 

 any rate, what little evidence is forthcoming suggests that 

 complex ions are very numerous, even at moderate dilutions, 

 and any such complexity will diminish the number of solute 

 par tides and consequently the osmotic effects. Kahlenberg 

 finds that solutions of diphenylamine in methyl cyanide show 

 abnormally low molecular weights, and yet are non-conductors 

 of electricity. Such a result perhaps indicates a dissociation 

 yielding products which are not electrically charged, or a 

 non-electrical double decomposition with the solvent. Until 



