The corresponding states correlation of McGlashan and Potter has been tested twice in order to to predict the second virial coefficients of the mixtures (methane + tetramethylsilane or 2.2-dimethylpropane) at four different compositions in the temperature ranges 303.16 K to 403.16 K and 323.16 K to 403.16 K, repsectively. Predicted values are essentially identical to those obtained by using the more tested correlation of Pitzer-Curl-Tsonopoulos. Predictions were improved significantly, to yield deviations of only (0 to 2) per cent, after correcting the pseudocritical temperature by an empirical device due to Gunn and Prausnitz.