AbstractMelting curves, viscosities and densities have been determined for the mixtures of 1,2,4‐trichlorobenzene + n‐decane and + n‐tetradecane. Derived thermodynamic excess properties (excess Gibbs energygEand excess volumevE) can be combined with literature data on trichlorobenzene + n‐alkane systems to establish an unusual trend of mixing properties with chain length of n‐alkane. Also viscosities of equimolar mixtures of trichlorobenzene with various n‐alkanes and of benzene with various n‐alkanes have been measured, in order to collect more material on the behaviour of n‐