Accession Number:

AD0613404

Title:

THE SPONTANEOUS TRANSFORMATION FROM MACROCRYSTALLINE TO MICROCRYSTALLINE PHASES AT LOW TEMPERATURES. THE HEAT CAPACITY OF MGSO4.6H2O,

Descriptive Note:

Corporate Author:

CALIFORNIA UNIV BERKELEY LOW TEMPERATURE LAB

Personal Author(s):

Report Date:

1955-03-07

Pagination or Media Count:

5.0

Abstract:

The heat capacity of MgSO46H2O was measured from 15 to 325K. Assuming crystal perfection at 0K. the entropy at 298.16K. was found to be 83.20 caldeg.mole. A table of thermodynamic properties from 0 to 320K. is presented. These results were obtained when the sample was not allowed to stand near 120K. for more than a short period. When MgSO46H2O is allowed to stand in the region near 120K. heat is slowly evolved. Heat capacity measurements starting at 15K., on sample thus treated, disclosed no anomaly near 120 and absorption of heat over a broad region with a maximum near 246K. Nitrogen gas absorption near 77K. showed that the evolution of heat was accompanied by the formation of microscopic phase regions. Barieau, Chu and Giauque had found that ZnSO4.6H2O behaves in an almost identical manner. The two crystals are isomorphous. Zinc sulfate hexahydrate has been reported by Copeland and Short to be unstable with respect to the reaction 6ZuSO46H2O 5ZnSO4.7H2O ZnSO4H2O below 21.5. Thus the most plausible explanation of the anomalous heat effects in both the zinc and magnesium hexahydrates is to assume their decomposition into other hydrates, a process so difficult in the solid state that only microcrystalline phase regions can be formed. Author

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Distribution Statement:

APPROVED FOR PUBLIC RELEASE