1958 年 78 巻 4 号 p. 391-394
Dissociation vapor pressure of diphenylhydantoin sodium hydrates was measured at a temperature between 20° and 50° using a differential tensimeter and it was found that mono-, tetra-, hepta-, octa-, and hendecahydrates existed in diphenylhydantoin sodium. An empirical formula log P=A-B/T can be given to relationship between the dissociation vapor pressure and temperature and the values of constants A and B for each hydrate system were calculated. It was proved that the transition temperature of 37.6°, 45.2°, and 51.3°, presumed from the solubility curve and viscosity-temperature curve in the preceding paper, agreed respectively with the transition temperature of hendecahydrate-octahydrate, octahydrate-heptahydrate, and heptahydrate-tetrahydrate. Comparison of monthly average humidity in seven areas in Japan and dissociation vapor pressure of the hydrates indicated that the heptahydrate was the most stable in air in a country like Japan with high average humidity.