The Stratifications of Hydroyen. 



403 



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. 



Fro. 4. 



The vacuum tube, K, is 8 inches between the terminals, and J 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.* 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. 



