Thermodynamic and Structural Studies of Polymorphism in 1,1,1-trichloroethane and 2,2-dichloropropane

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Abstract
Optical birefringence measurements have been made on the different solid phases of 1,1,1-trichloroethane and 2,2-dichloropropane with the object of establishing their ranges of stability and their interrelationships. The nature of the solid phase that is contiguous to the liquid seems to depend upon the amount of impurities present in the specimens. This result is confirmed by an extensive calorimetric investigation of two specimens of 1,1,1-trichloroethane containing 0.31 and 0.82 mol° of impurity respectively. A comparison of the calorimetric data with results published in the literature suggests that one or the other of two distinguishable phases I of solid 1,1,1-trichloroethane is stable in the phase I region. While some apparently conflicting results obtained previously are thus rationalized, it is not certain that still other phases I cannot be formed.