Abstract
LONDON. Royal Society, February 16.—Sir Archibald Geikie, K.C.B., president, in the chair.—W. Rosenhain and S. L. Archbutt: The constitution of the alloys of aluminium and zinc. In connection with researches on light alloys, carried out on behalf of the Alloys Research Committee of the Institution of Mechanical Engineers, the authors have studied the constitution of the Al-Zn alloys by pyrometric and microscopic methods, including the study of specimens after prolonged annealing at definite temperatures and after quenching. The results are represented in an equilibrium diagram differing materially from those previously put forward. The principal points of difference are:—(1) The liquidus curve shows a small break at a concentration of 85 per cent, of zinc, this break being connected with the formation of a definite compound of probable formula Al2Zn3. (2) In alloys under conditions of complete equilibrium the occurrence of eutectic ceases at a concentration of about 78 per cent, of zinc, although in ordinary slowly cooled alloys the eutectic can be traced down to the vicinity of 50 per cent. zinc. (3) At a concentration of about 78 per cent, of zinc, the solidus curve of the alloys rises abruptly from the eutectic line (380° C.) to a horizontal line of arrest points at 443° C. This line commences at the break in the, liquidus curve already mentioned, and extends to about 37 per cent, of zinc; between 78 and 40 per cent, this line represents the solidus, but near 40 per cent, the solidus bends upwards towards the melting point of pure aluminium. The reaction indicated by this line of arrest points is the formation of a compound (Al2Zn3) by the reaction of crystals of a solid solution of zinc in aluminium with the residual liquid. (4) A second horizontal line of arrest points of considerable intensity has been found at. 256° C. in alloys containing 99 to 35 per cent. of zinc. These heat evolutions are due to decomposition of the compound (Al2Zn3) into two phases, one of which is the saturated solid solution of Zn in Al, while the other is practically pure Zn. (5) The existence of a definite compound is indicated, stable only between 443° C. and 256° C., and having a zinc content of about 78 per cent., most nearly represented by Al2Zn3. Evidence for its existence is derived from the termination of the eutectic line and the position of maximum intensity of the line of heat evolutions just mentioned; this is strikingly confirmed by the micro-structures, which show the compound in the form of characteristic hexagonal dendrites. When decomposed (at or below 256° C.), it exhibits a duplex laminated “pearlitic” structure strikingly resembling the pearlite of carbon steel.—R. Whiddingfton: The production and properties of soft Röntgen radiation. Röntgen rays from ordinary bulbs are usually produced at generating potentials of between 10,000 and 100,000 volts. It is possible by using a special tube with a very thin aluminium window to experiment with rays generated at only a few hundred volts. The rays dealt with in this paper were generated at 1000 to 3600 volts. It has been found that such soft Röntgen rays have much the same properties as the harder rays usually experimented with. They produce ionisation in air, affect photographic plates, and can excite secondary radiations when incident on solid bodies. Their range in air, hewever, is not many centimetres. For many purposes a Röntgen radiation is sufficiently defined by a knowledge of (1) the total energy; (2) the penetrating powers in absorbing screens. These two properties have therefore been investigated in some detail, with reference particularly to the influence exerted by (1) the material of the antikathode; (2) the potential at which the rays are generated. The antikathodes used fall naturally into two groupings:—Group A.—Al, Pt. Group B.—Ag, Cd, Cu, Fe, Ni, Pb, Sb, Sn, Zn. The anti-kathodes of Group A emit secondary radiations, those of Group B do not. Experiment indicates that Al emits a soft characteristic, radiation of λ/ρ 580 (in Al). In order to arrive at a common explanation of a number of experimental results, it is suggested that this Al radiation disobeys the law of “Röntgen ray fluorescence” recently advanced by Barkla.—Prof. J. Eustice: Experiments on stream-line motion in curved pipes. In a paper on the flow of water in curved pipes, the author has shown that during the flow of water through a pipe, if a change is made from a straight to a very slightly curved form, there is an increased resistance to flow, which is very marked at velocities below the critical velocity. In order to find the cause of the increase in resistance, an apparatus was designed which provides for the distribution of six variously coloured filaments of dyed water into a glass pipe through which water is flowing. The positions of the filaments can be so arranged that in the passage of water from a straight to a curved pipe the directions of the stream-lines in any part of the tube can be investigated. The experiments show that the curvature of a filament is less than the curvature of that part of the pipe in which the filament is flowing, and if the velocity of flow increases the curvature of the filament increases. The filaments impinge on the outer wall of the pipe, and, flattening into bands, follow the surface of the pipe and cross over to the inner wall, where the filaments start again in their path along the main stream, until (if the pipe is sufficiently long) the filaments again meet the outer wall, when the return flow along the surface is repeated. A filament flowing in the central plane of the pipe, when reaching the outer wall, divides into two parts, which come together on the inner wall of the pipe; the other filaments flow through the loop which is thus formed. A filament not in the central plane remains on that side of the plane in which it enters the curved pipe. The experiments were extended to angle pipes, and the velocities were increased until turbulent motion was obtained. After flowing through a curved pipe or angle, vortices are generated which persist in a contiguous straight pipe.
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Societies and Academeis . Nature 85, 564–566 (1911). https://doi.org/10.1038/085564a0
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DOI: https://doi.org/10.1038/085564a0