The magnetic susceptibility of binary systems of organic liquids

Abstract

From the results of a large number of measurements with organic compounds Pascal has shown that the magnetic susceptibility of straight chain substances may be calculated from the susceptibilities of the constituent atoms, except in those cases where double or treble linkings occur. In such cases the susceptibility may be calculated if due allowance is made for the constitutive effect of the multiple bonds. It would therefore appear that the magnetic susceptibility of a mixture of two organic liquids should be capable of calculation, by the mixture law, from the values of its components. It has, however, been shown by many investigators, dealing with widely differing properties of organic liquids, that mixtures of these substances do not in most cases obey the simple mixture law. On the contrary, it is very difficult to find two liquids, which on mixing give a value for any physical property that is exactly the mean of those of its constituents. Several physical properties of organic liquids are similar to magnetic susceptibility, in that the property of the compound is largely an additive function of those of the constituent atoms and the linkings in the molecule. The investigation of many properties of liquid mixtures, such as vapour pressure, density, refractive index, dielectric constant, specific heat and other thermal quantities has shown that in the case of a large number of binary mixtures of organic liquids the value of a particular property differs from that calculated by the mixture law because of the influence of other factors such as, for example, intermolecular forces which bring about association, dissociation, and, in some cases, molecular compound formation. The examination of curves in which the value of the property under consideration is plotted against the molecular composition of the mixture frequently furnishes evidence of the existence of association, dissociation, and compound formation in such binary mixtures.