On the solubility of silver in mercury

Abstract

From the survey the following facts appear well established:- 1. The γ phase exists in the lattice structure of γ-brass, but it is not certain whether or no this is perfect. 2. Its chemical composition lies near 27 per cent silver - electron /atom ratio 1.592 - and its range of stability probably does not exceed one per cent in either direction. 3. This definitely excludes the composition Ag₅Hg₈ with 13/21 atom /electron ratio, from the permissible range. Such an exclusion is not unique; careful investigation by STOCKDALE (J. Inst. Met. 52, p.111, 1933) has shown that the range of the θ phase in the aluminium-copper series does not include the composition Cu Al₂, although it possess a typical intermetallic compound structure. This was confirmed by BRADLEY (ibid , p.117). 4. The discrepancies in observed data are probably due to the great difficulty in obtaining equilibrium for a phase whose maximum temperature of existence is 127°C. The extreme slowness of reaction in alloys at ordinary temperature is well known. 5. The suggestion that the ß (Ag₅Hg₄) constituent does not occur in mineral silver amalgams is well supported by radiological evidence, and may yield a solid constituent containing 27-28 per cent silver. If these minerals are to be regarded as in chemical equilibrium, a minor revision of the silver mercury diagram proposed by Murphy is necessary. This would make the ß constituent metastable at room temperature. In view of the very slow rate of reaction to which attention has been called by several workers (HUMPHREYS, MURPHY, GAYLER, TROIANO) this does not seem unreasonable. 6. The densities of the interrnetallic compounds are not sufficiently different from that of mercury to allow any conclusions to be drawn from the variation of this property with composition. The densities obtained for mineral amalgams are slightly but definitely higher than those for synthetic products, and accord much better with those calculated from lattice parameters obtained by radiology.