MEMOIR XXVI.] CAPILLARY ATTKACTION, ETC. 353 



ing disengaged, and a condensed mixture of atmospheric 

 air and those gases accumulated in the space a a, e e, the 

 gauge tube showing the extent to which Ihe condensa- 

 tion had gone. Now if the little cup/ had been filled 

 previously with lime-water, and the whole arrangement 

 introduced into a jar of carbonic-acid gas, the upper part 

 of the lime-water presently became milky, and after a 

 time a copious precipitate of carbonate of lime subsided. 

 This would readily take place when the gauge was indi- 

 cating a pressure of ten atmospheres. In like manner, 

 when a piece of paper covered with carbonate of lead 

 had been introduced, and a pressure of twenty-four and 

 a half atmospheres accumulated, on introducing the in- 

 strument into a vessel of sulphuretted hydrogen the pa- 

 per quickly became brown. So sulphuretted hydrogen 

 can pass through a sheet of India-rubber, and diffuse 

 into an atmosphere of oxygen, hydrogen, and atmos- 

 pheric air beyond, though it be resisted by a pressure 

 equal to that of eight hundred feet of water. 



The method of condensation here employed, because 

 of its freedom from mechanical concussions, enabled me 

 to continue these researches up to pressures of fifty at- 

 mospheres, without leakage, in comparatively slender 

 tubes, and even under these circumstances gaseous diffu- 

 sion seemed to take place without any restraint. 



In passing, it may be remarked that when water is 

 enclosed hermetically in a vessel, and a voltaic current 

 passed through it, decomposition ensues, a portion of the 

 gases making their appearance in the gaseous form, fill- 

 ing the small space occupied by the decomposed water, 

 and the remainder being absorbed by that liquid as fast 

 as it is given off. When the pressure is high, the di- 

 mensions of the vessel become sensibly greater, and the 

 little bubble of air accumulated exceeds in bulk the vol- 

 ume of the decomposed water. 



