An introduction to chemical crystallography / by P. Groth, Authorised translation by Hugh Marshall.

  • Groth, P. (Paul), 1843-1927.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to chemical crystallography / by P. Groth, Authorised translation by Hugh Marshall. Source: Wellcome Collection.

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    bisphenoidal, exhibit no crystallographical resemblances. (Cleavage and density apparently have not been determined.) Malic acid, H2C4H403, is crystallographically still insufficiently investigated. The acid ammonium salt of the racemic acid and that of the active acid crystallise quite differently ; the density is known in the case of the latter only. Benzoyltetrahydroquinaldine, C10Hi2NCOC6H5. The racemic substance has the density 1-2375, and is monoclinic prismatic ; the active one has the density 1-2114, and is monoclinic sphenoidal. The crystal forms of the two exhibit no similarity.1 Carvoxime, C](lH4NOH. Both the racemic and the active sub¬ stances crystallise monoclinic, and have very similar axial ratios, while the axial angles p show a greater amount of discrepancy. The density of the former is 1-126; that of the latter, 1-108 ; the solubility curves of the two are also different. Limonene tetrabromide, Ci0Hi2Br4. In the form of the racemic compound this substance, formerly called dipentene tetrabromide, has the melting point 1250, and density 2-225, and crystallises rhombic bipyramidal. The active substance, likewise rhombic, has a very similar habit, and axial ratios which differ only slightly from those of the former; the subsidiary forms, as also the symmetry, are of course different. Its melting point is 104°, and its density 2-134. An ethereal solution of equal quantities of the active and inactive substances yields no mixed crystals, but separate crystals of melting points 1250 and 104 respectively (Wallach). Benzylidene camphor, C10H14O.CH.C6H5. The racemic sub¬ stance has the melting point 730, and forms monoclinic prismatic crystals, totally different from the rhombic bisphenoidal form of the active components ; these have the melting point 98°, and the density, within the limits of experimental error, agrees with that of the racemic substance.2 As shown by these and other examples, racemic sub¬ stances in general possess a crystal structure different from that of the optically active components, as is the case with isomeric substances generally. As a rule, the racemic substance possesses the higher density, lower solubility, and higher melting point. When the melting point coincides 1 Pope and Peachey, Journ. C.S. 1899, 75> 1066 et set/.; Zeit. f Kryst. 34, 612 et seq. - Minguin, Zeits. f. Kryst. 1904, 39, 317.