The results unquestionably confirm that, for each of the materialsexamined, there exists a definite and fixed amount of water of hydration which isincapable of undergoing a normal freezing process. Additional water above this levelfreezes in a normal manner and begins to thaw out during rewarming at a temperaturedetermined by the spectrum of soluble constituents present and, therefore, characteristicof the particular material concerned. This recognition of a characteristic ‘eutectic’temperature which can be determined, in spite of the lack of sharpness of the transition,within quite narrow limits, and which is unaffected by the freezing treatmentapplied, suggests the existence of a lower limit to the range of temperature over whichfreezable water can normally be converted to ice. In respect of the materials for whichresults are illustrated in Fig. 2, the ‘eutectic’ temperatures lie between - 25” and- 40°C. It would therefore appear to be quite possible, indeed likely, that at thetemperatures used by some earlier workers for the determination of values for unfreezablewater included in Table 1, the freezing process was not complete and thatthe values themselves must therefore be erroneously high.
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