See Lehmann, Geschichte des Herzogtums Zweibriicken (Munich, 1867).
57 sqq.; Lehmann Haupt in Beitrage zur alten Geschichte, 1905, v.
Hist., Leges, iii., and by Karl Lehmann in the 4to series of the same collection.
Lehmann it melts at 168° (or at a slightly lower temperature in its water of crystallization) and on cooling forms optically isotropic crystals; at 125.6° the mass becomes doubly refracting, and from a solution rhombohedral (optically uniaxial) crystals are deposited; by further cooling acicular rhombic crystals are produced at 82.8°, and at 32.4° other rhombic forms are obtained, identical with the product obtained by crystallizing at ordinary temperatures.
Lehmann and (2) polymorphs in which the transformation proceeds in one direction only - termed " monotropic."
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