Societies and Academies

LONDON.Royal Society, June 3.-A. E. H. Tutton: The alkali perchlorates, and a new principle concerning the measurement of space-lattice cells. The crystallo-graphic character and optical properties of the perchlorates of potassium, rubidium, cassium and ammonium have been investigated. The crystal angles and goniometrical constants are progressive in the order of the atomic numbers of the alkali metals, the average change for the replacement of potassium by caesium being double as much as occurs when rubidium replaces potassium. Optical properties and the sizes, both relative and absolute, of the unit-cells of the space-lattice also show the progression with atomic number of alkali metal very clearly. The absolute dimensions of the cells have been found by a new principle. In an isomorphous series based on similar structure, if one member crystallises well and can be thoroughly investigated by X-rays and the cell dimensions determined in Angstrom units, the cell dimensions of all the other members can be calculated. The case of the perchlorates and barytes group affords the first, and an excellent, example. The structure and cell-dimensions of barytes are known with certitude. The cell-dimensions of the minute crystals of the isomorphous perchlorates of the alkalies have been calculated from their topic axial ratios and the barytes data. In one case a critical test has been possible, that of potassium perchlorate, X-ray analysis of which has been just adequate to afford the cell-dimensions; and these have proved to be practically identical with those calculated on the new principle. T. E. Stanton: On the flow of gases at high speeds. An experimental investigation was undertaken on the nature of the flow of a gas through orifices and nozzles at speeds in the neighbourhood of and exceeding the velocity of sound. The prediction of Osborne Reynolds that a minimum section of the jet would exist at that point in it at which the theoretical critical pressure p0 obtains has been fully verified. The magnitude of the minimum section and its position relative to the throat of the orifice or nozzle depend on the value of the receiver pressure. The conditions for dynamical similarity in jets from geometrically similar nozzles and orifices at speeds above the velocity of sound depend on the viscosity of the gas and not solely on the ratio of the speed to that of sound. A reliable method of measuring the velocity at a point in a jet moving at speeds above the velocity of