. Carnegie Institution of Washington publication. POTASSIUM, RUBIDIUM, AND CAESIUM. 11. \ 50 and 100 atmospheres, and this first reading was taken as the starting point of the determination. Minute air-bubbles were thus disarmed of possible injurious effects. As already suggested, a weighed quantity of mercury was now added through the open tube, and pressure was again applied. The added pressure necessary to break the electrical circuit cor- responded to the volume of the extra mercury introduced. This process was repeated until the highest pressure was reached, and thus were found the points
. Carnegie Institution of Washington publication. POTASSIUM, RUBIDIUM, AND CAESIUM. 11. \ 50 and 100 atmospheres, and this first reading was taken as the starting point of the determination. Minute air-bubbles were thus disarmed of possible injurious effects. As already suggested, a weighed quantity of mercury was now added through the open tube, and pressure was again applied. The added pressure necessary to break the electrical circuit cor- responded to the volume of the extra mercury introduced. This process was repeated until the highest pressure was reached, and thus were found the points on a curve which represented the difference between the compressibil- ities of mercury and glass. The mercury was now wholly removed, except for a small amount in the U-tube —enough to seal the bend. The rest of the left-hand side of the apparatus was then filled with paraffin oil of known com- pressibility, and the metal was introduced in the form of a closely fitting cylinder. The jacket was now placed once more in the Cailletet barrel, and once more the pressures corresponding to successive added portions of mercury were found. These new readings define the curve of the total compression of the liquid, the metal, and the residual mercury, all taken together. By subtracting the correspond- ing values from this first curve, and also that corresponding to the known weight of paraffin oil, results are obtained which represent the differences between the com- pression of the metal and a like bulk of mercury. From this the compressibility is very simply computed. In the case of rubidium and caesium an additional glass bulb was needed within the jacket. Correction for this was easily made, as will be seen. If the platinum wire is very finely pointed, the fine tube around it about mm. in diameter, and the mercury meniscus covered with perfectly clean water, the indications of this instrument are surprisingly constant and trustworthy. Even with a substance no more compressible
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