The Theory of Dissociation into Ions

Abstract

I AM very glad that Mr. Pickering has given further details of his experiment. From his former letter I did not gather that the number of acting units indicated by the freezing-point of the solution of 100H₂O+H₂SO₄ in acetic acid was as low as now appears. The result is most interesting, and seems to me to furnish strong evidence for the modification of the dissociation theory for which I am contending, under the belief that, in spite of the last paragraph of Mr. Pickering's present letter, it furnishes the best explanation of all the facts. Had the number of acting units indicated been nearer 100—say 90, or more—it would have been possible to explain the experiment in the first way which I suggested, for the freezing-point of a solution of water in acetic acid shows that some of the solute molecules are polymers of H₂O (Raoult's value for the molecular depression is 33˙0, as compared with 38˙8 found from Van't Hoff's formula, which agrees well with Raoult's values for other substances). This would reduce the number of acting units in the case of the mixed solution also, and even complete dissociation of the sulphuric acid would be insufficient to bring that number up again to 100.