The Magnetic Anisotropy of Crystalline Nitrates and Carbonates. K. S. KRISHNAN AND C. V. RAMA~. (Proc. Roy Soc., A 772.) The connection between the crystalline structure of solids and their magnetic properties has recently been accentuated. In this paper the authors discuss the lack of magnetic symmetry in certain nitrates and carbonates that are diamagnetic. "These substances are especially simple because as is well-known from the work of Kossel, Bragg, and others, they consist of charged ions held together by electrostatic forces, so that we can attribute the magnetic anisotropy of the crystal to that of the individual ions. Thus, for instance, in the case of sodium and potassium nitrates we may reasonably look for the explanation of observed magnetic anisotropy of the crystal in the structure of the nitrate ion, since presumably the metallic ions are more or less isotropic." NaNO3 and CaCO3 both belong to the trigonal system. In both the magnetic susceptibility is greater parallel to the trigonal axis than perpendicular to it. For the nitrate the susceptibilities in the two directions are 29.5 and 24.1 X -lO6; and 40.6 and 36.4 X -IO ~, for the carbonate KNO3 and CaCO, (aragonite) are both rhombic and show the greatest susceptibility parallel to the "c" axis.
Making use of data on magnetic double refraction, on the optical constants of the molecules, and on the depolarization of scattered light the authors calculate the directional difference of the susceptibilities of the two nitrates and find them to agree quite well with the measured values. In the NO3 group there are three oxygen atoms at the corners of an equilateral triangle, the nitrogen atom being at the center.