Diffusion is slower in phenylsilicones in proportion to the exponent of the phenyl content and in all silicones is slower in proportion to the exponent of the density. Diffusion is anomalous in cold chromatographic grade silicones, especially with long-chain n-alkanes, yeilding skewed peaks and, in the methyl-silicones, high diffusion coefficients. The anomaly is less apparent above 150°C and with low molecular weight methylsilicones.