In the present paper, the molecular interaction between the two organic molecules has been discussed from the view-point of the change of specific volume on the various kinds of organic mixtures. The results are as follows :
1). In the mixtures of benzene and non-polar solvents, acid or ester, the specific volume of the mixture generally increases by the mixing.
2). In halogen-substitutes of benzene and benzene, or benzene compounds including nitrogen and benzene, the specific volume generally decreases by the mixing.
3). In the two component mixtures of benzene and aniline, pyridine or dimethyl-o-toluidine, the sign of the increment of the specific volume varies from positive to negative according to the mixing ratio.
4). In some other systems such as benzene and phenol, alcoholor ethyl-aceto-acetate, the change of their specific volulme is very complicate.
5). The effect of the temperature on the change of specific volume is also very characteristic ; in benzene and aniline, pyridine or o-chlorophenol, the increment of the specific volume reduces to zero value at a fixed temperature.

　二成分系混合溶液の相互作用は，従来，いろいろな角度から研究されており，電解質溶液では水和現象究明として比体積が取り上げられ，また有機物質系では赤外吸収・誘電率等の僅かな変化を観測する方法，また，村上・藤代らはalcohol-keton系，alcohol-hexane系につき，混合熱を測定している。
　本報ではbenzeneを中心とする有機混合物の密度に着目し，相互作用のないときの比体積と，実測して得られた比体積の差から，系の相互作用を検討した結果を述べる。