MEMOIR XXVI.] CAPILLARY ATTRACTION, ETC. 



357 



Fig. 82. 



at first too thick, they expose too small a surface to the 

 atmosphere to which they are subjected, and it is not 

 until the close of the experiment that the action becomes 

 rapid. But a bubble at once exposes a large surface, 

 and by using proper precautions there is no difficulty in 

 preserving it for an hour, or even much longer. 



The quickness of these motions is very well illustrated 

 by the following experiment. If 

 a glass flask, a a, be rinsed out 

 with ammonia, and then by means 

 of a bent glass tube, b b, narrowed 

 at its projecting extremity, a soap- 

 bubble, <?, be blown therein, the air 

 from the bubble being immediate- 

 ly drawn into the mouth without 

 a moment's delay, the strong taste 

 of the ammonia will be perceived. 

 Or if a rod dipped in hydrochloric 

 acid be presented to the projecting end of the glass tube, 

 as the bubble slowly collapsing presses out its contents, 

 copious white fumes arise. Care must be taken that no 

 drop of water obstructs the egress of the gas from the 

 bubble, and that the cork fits the flask with a slight 

 leakage. This, therefore, shows that va- 

 pors will pass through barriers having no 

 proper pores, the transit taking place in- 

 stantaneously. 



I constructed an apparatus (Fig. 83) for 

 exposing gases to each other with the in- 

 tervention of a soap-bubble, and subse- 

 quently measuring and analyzing them. 

 a a is a tin saucer about three inches in 

 diameter and half an inch deep; into it 

 water can be poured ; it also serves as a 

 Fig. S3. platform to support a small bell-glass, b. 



