(1) Á slightly modified form of Haber's vibrating quartz fibre manometer is described.2. (2) The vapour pressure of mercury is measured at room temperature. The mean of the results, corrected to 20° C., is 1·30.10-3 mm.3. (3) The vapour pressures of cæsium and rubidium at various temperatures between 50° C. and 139° C. are measured. The relation between log p and 1/T is found to be approximately linear over the range considered, and the results can be represented by the formulæ 4. (4) The chemical constants of the two metals are calculated; the values obtained are 1·64(0)± ·16(4) for cæsium and 1·36(6)±·18(4) for rubidium. If C=l·5 1og M + C0, where M is the molecular weight, the values obtained for the absolute chemical constant C0 are -1·54(5)±·16(4) and 1·53(2)±·18(4). The theoretical value of C0 is -1·608, so that the results are in agreement within the error.5. (5) The value of Trouton's coefficient λTB/TB (where TB is the boiling-point) is worked out; giving 18·2 for cæsium and 19·9 for rubidium.6. (6) The chemical constants for both metals are above the theoretical value. The possible reasons for this are discussed.7. (7) Some measurements are made on the amount of mercury vapour passing through a trap of the ordinary type when cooled in CO2 snow and ether. The mean value is found to be 1·84. 10-4 mm. It is shown that the trap is more efficient when filled with copper turnings; the mean value in this case being 1·17. 10-4. When the trap is cooled in liquid air the readings with and without copper turnings in the traq are in complete agreement.
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D. H. Scott (1924) studied this question.