Magnetic behaviour of organic crystals

The interesting observations of Sir William Bragg on the deportment of crystals of naphthalene in a magnetic field (Nature, Supplement, May 7, 1927) have been followed up quantitatively in this laboratory, and some very significant results have been obtained. It is found that the diamagnetic anisotropy of naphthalene is extremely pronounced, the susceptibilities along the three magnetic axes of the crystal being approximately in the ratios 16: 7: 4. That such a high degree of anisotropy is to be expected in aromatic compounds is indicated by the data for magnetic birefringence in liquids, as had indeed been shown earlier (C. V. Raman and K. S. Krishnan, Proc. Roy. Soc., A, vol. 113, p. 511; 1927). Mr. S. Bhagavantam, who made the measurements, finds that the axes of maximum diamagnetic susceptibility and of minimum optical dielectric constant in naphthalene crystals are approximately coincident. This observation-explains why organic liquids derived from naphthalene, and indeed also aromatic liquids generally, exhibit a strong positive magnetic birefringence. We may further expect to find that in aromatic compounds generally, the magnetic and optical characters are linked together more or less in the same way as in naphthalene crystals