both those of the barometer EE, as well as those in C and D, by means of a cathetometer Z (fig. 4) constructed specially for the purpose. This consisted essentially of a vertical steel axis carrying two horizontal telescopes with cross wires, which were set one at each level, and then the axis rotated to the scale F, and the heights registered to .1 millim. This method was necessitated from the want of steadiness in the floor of the room in Durham School Laboratory, where the majority of the experiments were carried out. The same arrangement (which is very convenient as well as accurate) was also used in the later experiments which were carried out under more favourable conditions in the gas analysis room of the Cambridge University Chemical Laboratory.
Fig. 2 shows the earlier form of measuring vessel used when the varying pressures and volumes were both measured. The tubes B, C, and D were all of the same diameter, so that no capillarity corrections were required.
Fig. 3.
- R, Flask for water to be boiled.
- S, Flask for sodium.
- T, Washing tube, with very dilute hydrochloric acid.
- U, Exit tube for hydrogen, sealed to U (fig. 1) when in use.
- W, Small india-rubber stopper.
Fig. 3 shows the simple apparatus employed for the preparation of hydrogen from sodium by acting on it with steam. When it was used the end of the tube U was sealed to the tube U (fig. 1), which contained palladium in its wider part, P. The only india-rubber connection is at W, where there is a stopper of that material, but diffusion through this was practically impossible to any injurious extent, as the space between the tubes was very narrow and the stopper was 6 to 8 millims. long, and after setting up the apparatus it was sealed over with paraffin containing enough vaseline to prevent its cracking, whilst it allowed of its being easily shaken.
