The heat capacity and principal susceptibilities of thulium ethylsulfate have been measured in the range 15deg;mdash;300deg;K and 1.3deg;mdash;200deg;K, respectively. The heat capacity of lutetium ethylsulfate has been measured in the range 15deg;mdash;300deg;K. The contribution of the 4felectrons in Tm to the heat capacity of thulium ethylsulfate has been evaluated experimentally by making an assumption concerning the difference in the lattice heat capacities of Tm and Lu ethylsulfates. The contribution of the 4felectrons in Tm to the heat capacity and principal susceptibilities has been calculated using the angular part of the crystal field matrix elements calculated by Stevens and Elliott K. W. H. Stevens, Proc. Phys. Soc. (London)A65,209 (1952). R. J. Elliott, Revs. Modern Phys.25,167 (1953); R. J. Elliott and K. W. H. Stevens, Proc. Roy. Soc. (London)A219,387 (1953);A218,553 (1953), and two sets of crystal field parameters currently available in the literature E. Y. Wong and I. Richman, J. Chem. Phys.34,1182 (1961); J. B. Gruber and J. G. Conway,ibid.32,1531 (1960). The experimental results indicate that the crystal field parameters of Wong and Richman are more nearly correct than those of Gruber and Conway.
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