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    Abstract

    Swansea. Institute of Metals, September 22.—F. L. Brady: The structure of eutectics. An attempt has been made to correlate the micro-structuré of solidified eutectics, mainly those between metals and metallic compounds, with the physical properties of the component metals. The surface tension of the molten metal and the cohesive force acting during crystallisation seem to be the main forces influencing the final structure. The eutectics examined fall into three classes: “globular,” “lamellar,” and “angular.” The structures agree with what would be expected from theoretical considerations of the effects of surface tension and cohesion.—M. Cook: The antimony-bismuth system. The two metals form an isomorphous series of alloys. The liquidus curve is perfectly smooth and the solidus is horizontal at 2700 C. up to 60 per cent, of antimony, after which it rises steeply to the freezing-point of antimony. Chill-cast and slowly cooled specimens reveal duplex structures, but with prolonged annealing—550 hours at 275° C.—the alloys become homogeneous. Twin crystals and peculiar banded effects were observed in some of the annealed specimens. Possibly the twin crystals are formed during solidification of the alloy by stresses due to expansion, and grew on annealing. The nature of the “bands” has not been definitely ascertained, though they are not considered to be slipbands.—A. Jefferson: The cause of red stains on silver-plated work. The Sheffield Silver Trade Technical Society appointed a committee to examine this subject. It was established experimentally that the red stain is caused by the indiscriminate use of rouge in the finishing and polishing processes, through the absorption of the rouge into the open pores of the heated surface, the heat being evolved by the friction of the hand or finishing “dolly.”—Q. A. Mansuri: Intermetallic actions. The system thallium-arsenic. By thermal and microscopic analysis it was shown that thallium and arsenic do not act chemically with each other nor do they form solid solutions; they alloy in all proportions. Arsenic dissolves in molten thallium and lowers its freezing-point until a solution of 8.01 per cent, arsenic freezes at the eutectic temperature of 215° C. Then the freezing-points of the alloys rise gradually to 240° C, All alloys containing from 13 to about 40 per cent, arsenic begin to freeze at 240° C. and are made up of two layers-the upper layer rich in arsenic while the lower rich in thallium. Beyond 40 per cent, arsenic, to nearly pure arsenic, the solution is uniform and the two layers disappear. By heating such substances in evacuated, sealed glass tubes and applying the hot junction of the couple in close contact with the outside of the glass tube, the couple is almost as sensitive as when dipped in the molten substance.—F. Johnson and W. Grantley Jones: New forms of apparatus for determining the linear shrinkage and for bottom-pouring of cast metals and alloys, accompanied by data on the shrinkage and hardness of cast copper-zinc alloys. The shrinkage values of chill-cast copper-zinc alloys were higher in general than those obtained for sand-cast bars by previous investigators. Pure electrolytic metals were used, and most of the alloys were poured at a temperature interval of approximately 115° C. above their liquidi, the mould being kept at a constant temperature by a jacket of water maintained at the boiling-point. The bottom-pouring apparatus has the advantage of (a) control of pouring temperature; (b) facility for registering temperature of metal; (c) absence of delay between attainment of required pouring-temperature and release of metal into the mould; (d) control of rate of pouring; (e) exclusion of dross from stream of metal; and (f) mitigation of “zinc-fume.” Uniformity of hardness was secured by annealing. For the annealed bars the Brinell curve snowed an increase of hardness over the range ioo to 88 per cent, copper. From 88 to 72 per cent, copper hardness was constant, a slight fall setting in at about 72 per cent, copper and persisting to 63 per cent., at which point a rapid increase set in with, the appearance of the β-constituent. With the exception of a small dip in the curve, between 53 and 50 per cent, copper, the increase is maintained to 45 per cent, copper. The changes of scleroscopic hardness with composition are similar but less pronounced. The hardening capacity of the a-brasses under cold-work increases rapidly with increase of zinc up to a maximum near 75 per cent, copper. The rolled strips, after close annealing, were re-tested for hardness; the range of uniform hardness is slightly restricted and the succeeding fall (between 70 and 63 per cent, copper) is more pronounced.— F. W. Harris: The hardness of the brasses, and some experiments on its measurement by means of a strainless indentation. The theories generally advanced with regard to the connexion between hardness and internal constitution have been, in the main, substantiated. A slight maximum occurs in the middle of the α-phase and a small depression in the (β-phase. The “absolute” hardness for the series was compared with the Brinell hardness by means of curves.

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