358 CAPILLARY ATTRACTION, ETC. [MEMOIR XXVI. 



Through its centre at c passes a glass tube,/, one eighth 

 of an inch in diameter, the upper extremity of which is 

 cemented into a hole of the same size in a round, thin 

 piece of copper, d, about half an inch in diameter ; the 

 other end of the pipe opens into another small bell-glass, 

 &, through a perforation in its top, the communication be- 

 ing capable of being cut off by means of a stop-cock, g. 

 The apparatus is used as follows : The upper bell, being 

 taken off the platform, is filled with any gas to be tried 

 oxygen, for instance and is placed aside on the shelf 

 of a pneumatic trough. The lower bell-glass is then filled 

 with water by depressing it in the trough ; and the stop- 

 cock being closed, five hundred measures of hydrogen, for 

 instance, are thrown into it. After seeing that the cop- 

 per plate d is free from moisture, a drop of water ren- 

 dered viscid by soap is placed upon it, exactly where the 

 orifice of the tube f opens. The upper glass containing 

 the oxygen is now placed upon the tin saucer platform 

 as in the figure. The lower glass is next depressed in 

 the pneumatic trough, and as soon as the cock is opened 

 a bubble of hydrogen containing five hundred measures 

 expands, the spare oxygen escaping from the edge of the 

 upper glass through the water in the tin saucer. The 

 cock is next closed, and the apparatus placed on the 

 trough shelf as long as the operator desires the experi- 

 ment to continue. Keeping that position, when the cock 

 is once more opened the gas passes into the lower bell 

 until the bubble has entirely collapsed, when the cock is 

 again closed, the contents of the bubble being now ready 

 for measurement and analysis. As the gas was passing 

 from the bubble into the lower bell, the water rose from 

 the tin saucer into the upper bell, confining the gas that 

 was outside of the bubble. This, by the common mode 

 of manipulation, is to be transferred from the tin plat- 

 form to the shelf of the trough for inspection. 



