216 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
219. — Seventh charge, pressure 1*6656 m.m., 2191 M, 1200 cells would not 
pass; 2400 cells, C. 0'02728 W. The cup-shaped strata became longer, and 
curved at the end, reminding one of a Phrygian cap. 
220. — Eighth charge, pressure 1*9265 m.m., 2534 M, 2400 cells, C. 0*02728 W ; 
only a confused discharge. 3600 cells, C. 0 ’03 6 20 W ; very deep cup-shaped 
steady blue strata, as deep as those in fig. 7, Plate 1 6, but not, like them, 
tongue-shaped. C, F, and G lines visible with spectroscope. 
221. — The absorption chamber was now connected with the tube. With 3600 
cells, phenomena in the reverse order were obtained. The pressure was 
observed -to have fallen in a few minutes to 1*003 m.m., 1318 M; in 10 
minutes to 0T245 m.m., 164 M ; and in 45 minutes to 0’0217 m.m., 28 M, 
when it required 4800, and subsequently 6300 cells to pass. At first when 
the saucer-shaped strata had disappeared, twenty-one disc-shaped strata pre- 
sented themselves ; these widened out, and there were successively sixteen, 
fourteen, and twelve, becoming like figs. 8, 9, 11, and 12, Plate 16, respec- 
tively. When the two last phases were produced, the hydrogen lines could 
not be seen either in the strata or the glow on the negative ring, but, instead 
of them, mercury lines came out strongly/''" There is reason to think that 
at this stage there was little gas, except mercury vapour, in the tube. 
It is to be observed that, with a very high degree of exhaustion, the 
tongue-, and saucer-shaped strata are no longer produced in a hydrogen vacuum, 
and that the strata assume the disc-form usual with carbonic acid, air, and 
nitrogen. 
Tube 81, 2 5 '5 inches between the terminals, diameter 0*875 inch. 
Carbonic Acid. 
222. — This tube is connected with a smaller one containing a stick of potash, 
see 81, fig. 37.t The current of 11,000 cells will only just flash across in one 
direction after the tube has remained at rest for some months so as to 
allow of the complete action of the potash. On heating the potash bulb 
gas is given off, and then the current of 2160 is sufficient, the maximum 
current with this battery being 0*00238 W. On heating the bulb still more 
it required 3240 cells to pass, and ultimately this was insufficient; by 
allowing the potash bulb again to cool the current of 3240 cells passed, 
and very close strata were produced, nine in an inch ; then, as it still further 
* Hittoef (Pogg. Ann. cxxxvi., 1869, pp. 1-31) measured tlie quantity of mercury vapour from his 
pump absorbed by a silver surface. He found it amounted in certain circumstances to 0 - 25 milligramme 
per square centimetre per diem. Morren (Ann. de Chim. iv., 1864-5, pp. 325-352) describes the 
difficulties he encountered from the presence of the mercury vapour as well as of other gases which 
he believes are usually dissolved in mercury. 
t Gassiot describes experiments with such a tube, Roy. Soc. Proc. x., 1860, p. 402. 
