dry caustic potash; the second, G, and the third, H, tubes containing phosphoric anhydride. Between the second phosphoric anhydride and the vacuum tube is another tube having sealed on to it, comb-like, seven projecting arms, J J, each containing a strip of palladium foil saturated with hydrogen.
Fig. 4.
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The vacuum tube, K, is 8 inches between the terminals, and ¾ inch diameter; it comes next to the comb, and then between it and the pump is a battery of tubes, each 12 inches long, to keep out the mercury. The first tube, L, is divided by a constriction in the middle, and contains, in the half next the vacuum tube, bright metallic copper, in the other half sulphur. The three next tubes, M, M, M, contain sulphur, but in the middle of each are placed a few grains of iodine separated from contact with the sulphur by a plug of asbestos on each side. The sulphur is prepared by keeping it fused at a temperature a little below its boiling-point till bubbles cease to come off, so as to get rid of water and hydrogen compounds. It is then allowed to cool, and is pounded and sifted so as to get it in the form of granules, averaging a mm. in diameter. Ignited asbestos is packed at each end of the tubes to keep the contents from blowing out when the vacuum is proceeding, or air is suddenly let in.[1] Next follows a tube, N, N, constricted in the middle, containing in the first half phosphoric anhydride, and in the second finely powdered dry caustic potash. A tap, 0, connects the apparatus with the pump, to prevent diffusion of mercury when the pump is not in use. All parts of the apparatus were built up in place and sealed together with the blow-pipe. The glass was new, and the apparatus had been kept apart from mercury until it was sealed together.
The apparatus was exhausted from air, the tap E being closed and
- ↑ An apparatus of this kind was briefly described by the author in a paper read before the Royal Society in 1885 (" Radiant Matter Spectroseopy Part II, Samarium," 'Phil. Trans.,' vol. 176, p. G93, June 18, 1885). The apparatus was used to prevent mercury from getting into the small radiant-matter tubes employed in the research.
