On the spontaneous crystallisation and the melting and freezing point curves of mixtures of two substances which from mixed crystals and posses a minimum or eutectic freezing point. —Mixtures of azobenzene and benzylaniline

The behaviour of mixtures of naphthalene and β-naphthol has already been investigated, and the freezing and melting point curves and the curve of spontaneous crystallisation for these mixtures described.* These substances were found to form a continuous series of mixed crystals, on a curve of Roozeboom’s Type 1, the melting and freezing points of all the mixtures lying between the melting points of the pure substances. The behaviour of mixtures of monochloracetic acid and naphthalene was also investigated, for it was stated by Cady that these substances form mixed crystals of Roozeboom’s Type 5, whose melting and freezing point curves exhibit a minimum or eutectic freezing point. Experiments were therefore made with these substances with the object of determining the form of the curve of spontaneous crystallisation, or supersolubility curve, for mixtures of this type. No sign of the formation of any mixed crystals was observed, however, in a lengthy series of experiments, and it was shown that naphthalene and monochloracetic acid give the ordinary V-shaped freezing point curve for the solutions of two substances in each other, similar to that already obtained for mixtures of salol and betol,§ the only new feature being introduced by the existence of three modifications of monochloracetic acid. The monochloracetic acid and naphthalene mixtures having thus failed as an example of mixed crystals possessing a minimum or eutectic freezing point, another attempt was made to obtain a pair of substances with convenient melting points which form mixed crystals and possess the melting and freezing point curves with minimum eutectic point characteristic of Roozeboom’s Type 5.