ABSORPTION OF GASES. 321 



or is forced into the liquids by means of pumps which 

 produce great pressure, as is the case with artificial 

 mineral waters. In a corked bottle containing such a 

 liquid, great pressure is exerted upon the surface by the 

 jriis, as long as the bottle is closed ; but, on opening the 

 bottle, the compressed gas above the surface of the 

 liquid escapes, and the pressure sinks to that of the at- 

 mosphere ; in consequence of this diminution of pres- 

 sure, the dissolved gas escapes in large quantities, the 

 liquid frothing up and effervescing. 



The absorption of carbonic acid by water may be 

 shown by means of a test-tube, of a size which just 

 illows the mouth to be closed with the thumb. It is 

 filled with water, inverted mouth downward into a 

 vessel filled with water, and filled to about three-fourths 

 with carbonic acid. As soon as this is done, the mouth 

 s closed with the thumb under water, the test-tube is 

 :aken out, thoroughly well shaken, its mouth again 

 )laced in the water, and the thumb withdrawn. Even 

 Before this, the thumb is perceptibly pressed into the 

 nouth of the tube by the pressure of the external air, 

 vhich is greater than the pressure inside the tube. A 

 'onsiderable force will be required to open the tube 

 mder water, and when this is done, water enters it to 

 upply the place of the absorbed carbonic acid. The 

 ube may be again withdrawn, and the shaking re- 

 peated ; each time more carbonic acid will be absorbed, 

 intil finally nearly the whole space inside the test-tube 

 is filled with water. 



Gases exhibit the phenomena of diffusion more gene- 

 ally than liquids, because all gases form mixtures with 

 me another, while many liquids cannot be mixed. Gases 



