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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    bismuth. Amongst those compounds in which these elements have a trivalent character there is regularly isomorphous replacement —in the oxides, sulphides, iodides, and especially in numerous natural thio-salts (the thiarsenites, thiantimonites, and thio- bismuthites). As quinquivalent elements, phosphorus, vanadium, and arsenic replace one another in the apatite—Ca5Cl(P04)3— group, and in numerous isomorphous groups of hydrated phos¬ phates and arsenates (the corresponding vanadates have been less fully investigated crystallographically); the compounds P(C2H5)3(C,H4Br)Br and As(C2H5)3(C2H4Br)Br, which crystallise cubic, can also be looked upon as isomorphous. Whilst niobium and tantalum replace one another isomorphously in all known cases (fluo-compounds, tantalates and niobates) the question of the isomorphism of the oxides Nb205 and TaoCb with V205 requires further investigation. VI. Oxygen group (bivalent, quadrivalent, and sexivalent elements).—A true isomorphous replacement of oxygen by the succeeding members of the group does not exist, and even very complicated sulphur compounds are not isomorphous with the corresponding oxygen compounds ; thus, the thiosulphates crystallise differently from the sulphates, and not only carbamide (urea) and thiocarbamide, but also their phenyl derivatives—even diphenylcarbamide and thiocarbanilide, notwithstanding the size of their molecules—are different. On the other hand, there is unmistakably a certain analogy in the cubic structure of certain exceedingly simple compounds of the two elements, as between cuprous oxide and sulphide, magnesium oxide and sulphide, zinc oxide and sulphide (in this case there is also agreement in the symmetry for a second—a hexagonal—modification); also between the oxides and sulphides of calcium, strontium, and barium ; and, finally, between the spinels and certain analogous thio-salts (linneite, Ni3S4). The agreement between certain metallic tellur- ides, which crystallise cubic, and the corresponding sulphides and selenides, must, in the same way, be looked upon as constituting no true isomorphism ; the other compounds of tellurium do not agree crystallographically with the compounds of sulphur and of selenium. In this group the most important series, as regards isomorphous replacement, are formed by the elements sulphur, chromium, and selenium, when these have a sexivalent character. The rhombic potassium salts, K2S04, K2Cr04, and K2Se04, have been mentioned