The accurate determination of the freezing-points of alloys, and a study of valency effects in certain alloys of silver

Abstract

In the alloys of silver with the four elements immediately following it in the Periodic Table, the silver rich alloys give rise to primary substitutional solid solutions for which the phase boundaries in the equilibrium diagram show well-defined valency effects. When the diagrams are plotted in atomic percentages, the liquidus and solidus curves fall more steeply with increasing valency of the solute, whilst the extent of the solid solution becomes less. It was shown (Hume-Rothery, Mabbott and Channel-Evans 1934) that, to a first approximation, the liquidus curves followed a simple valency rule, such that alloys of identical equivalent composition had identical freezing-points, and, hence, in dilute solutions where the liquidus curves were straight lines, the atomic depression of freezing-point was proportional to the valency of the solute. The experimental errors of 1 or 2°C. in the freezing-point data prevented an exact proof of a whole number law, and the present paper describes more accurate determinations of the freezing-points of these alloys. The first part of the experimental work was carried out by one of the authors (W. H. -R.) working alone, and the later work by the two authors together. It is convenient to refer to the two series of experiments as the early work and the later work respectively. In order to increase the accuracy of the liquidus determinations it has been necessary to examine many sources of error, and this work is described in 2; 3 contains the experimental results, which are discussed in 4.