DWOWHXSM OF SIJLFATEIAZOLE 97plotted from the data should present unique characteristics. This is not obvious in the figure though the curves have attained a linear form from about this temperature to the lowest temperature investigated which was -50'. Clearly we may not describe the water which freezes only a t temperatures below -22' in terms of ordinary phase equilibria. That which freezes at temperatures between zero and -2 2 O might be so described if it is considered as compressed but other evidence indicates that orientation of the dipoles would complicate the interpretation. In conclusion it may be stated that the present data are in general agreement with the previous studies".' and while compression occurs a t the solid-liquid interface, the properties of the liquid are additionally modified in this region.summary By means of the calorimetric method, determinations have been made of the unfrozen water on the surface of wetted silica gel and carbon a t temperatures from 0 to -50'.Basing a comparison on unit quantities of the solids, the silica binds the water more strongly than the carbon.The entrance of the new drug, sulfathiazole (2-sulfanilamidothiazole),' into the field of chemotherapy made a survey of its physical and chemical properties essential. In the course of this study, it was found that sulfathiazole occurred in two distinct crystalline forms. The conditions for the existence and isolation of these dimorphs and their physical properties are herein presented.Hexagonal Form.-When sulfathiazole was crystallized from water, acetone. or ethyl or methyl alcohol, hexagonal prisms ( Fig. 1) were formed. They were obtained easily by preparing a saturated solution of the material in ethyl alcohol on the steam-bath, removing the container from the bath and allowing to cool slowly to room temperature. The crystals were then filtered off and dried in the air. On heating the hexagonal prisms on the Fisher the other hand, if the temperature was raised slowly, most of the crystals would have become opaque before reaching 173'. micromelting point stage and observing under the microscope, part of them remained clear and melted at approximately 173 to lis0, while others suddenly turned white or opaque throughout and did not melt until the temperature reached 2W202". This indicated that some of the crystals had undergone a transition to the higher melting form, and the extent of this transition has been found to depend to a large extent upon the rate of heating. Thus, if the stage was preheated to about 175', it was possible to observe all the crystals melting a t this temperature. On (11 P-binder and Wdtcrri. 'In19 JOUINAL, 61, 2032 11839).Fig. 1.-Hexagonal prisms ( X SO)Rod Form.-An attempt was made to isolate a second type of crystal by fractional crystallization from hot ethyl alcohol; however, all fractions obtained in this manner were of the hexagonal form. Consideration was then given to the fact that when the hexagonal form became opaque upon heating on the melting point stage, it had in reality undergo...
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