plane surface and the vapor phase, become identical-which is just what Donnan has postulated. Is it not more than likely that both these hypotheses present phases of the truth and that, as Smoluchowski has pointed out, local dense spots of varying volume and density are formed in a nearly saturated solution and that some of these, when once formed, are stable, for the reasons which Thomson and Donnan have given? As to the size of these drops, it seems possible, since it is related to the

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... tension, that the size may vary with different liquids and also with the temperature for the same liquid. The amount of supersaturation possible is regulated by the size of these drops. summary. I . The degrees of supersaturation of four solutions of liquids in water have been measured. In the cases of nitrobenzene and carbon disulfide, the existence of supersaturation has been definitely established. 2 . The solubility of nitrobenzene in water has been measured a t three different temperatures. 3. The solubility of water in nitrobenzene has been measured at six different temperatures. 4. Various important theories have been correlated and an attempt made to use them to explain the phenomena observed. 5. A change in the density and other physical properties of small drops with the radius has been suggested as fulfilling one of the conditions in Donnan's theory of the critical opalescence. W~N I P B G , MANITOBA.