The Monte Carlo method of computation has been used to obtain some equilibrium properties of bcc binary solid solutions whose atoms interact according to the Ising model. Four cases have been treated: (a)N=128,c=frac12;, (b)N=1024,c=frac12;, (c)N=1024,c=3/8, and (d)N=1024,c=frac14; (Nbeing the total number of atoms andcthe fraction of one kind.) In all cases the heat capacity has a wellhyphen;defined maximum. At the equiatomic composition, the height of this maximum is greater in the larger crystal. Discontinuities in thermodynamic properties were not observed, and it seems reasonable that the orderhyphen;disorder transition in an infinite crystal would be characterized by an infinite heat capacity as calculated by Onsager and others for twohyphen;dimensional crystals. Comparison of the results with experimental properties of bgr;hyphen;CuZn suggests a remarkable applicability of the Ising model to this system. The potentialities and limitations of the Monte Carlo method for systems with phase transitions are discussed.
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