320 ABSORPTION OF GASES BY LIQUIDS. 





air upon that portion of the plate which was covere 

 with the paper is in a different state from that whic 

 has been breathed upon. 



A common window pane will serve for this experiment, provide 

 it be not too warm, in which case no vapour would be deposited upc 

 it. It should be rubbed, in order to remove the air from it, with 

 clean dry cloth, applying strong pressure but rubbing slowly, so ; 

 not to heat the plate too much. A loose pane which may be place 

 upon a flat surface (layers of paper upon a table, or somethir 

 similar) is not so easily broken. The experiment does not succee 

 so well with glass not previously well cleaned. 



A similar attraction takes place between the molecule 

 of liquids and gases ; liquids are equally with solic 

 capable of absorbing gases. The absorption of a gas b 

 a liquid is mostly called solution. Water dissolve 

 various gases in different quantities, but of the sam 

 gas there is always less absorbed by hot water than b 

 cold water. Fresh spring water contains a quantity of a 

 in solution; if it is allowed to stand in a glass, in a roon 

 so that it gradually becomes warmer, a portion of tl: 

 air separates in small bubbles which adhere to the side 

 of the glass. The separation of the dissolved air ma 

 be observed still better by heating water in a test-tub 

 but not so much as to make it boil. Best of all it ma 

 be observed, by placing a glass of fresh water und< 

 the receiver of an air-pump and exhausting it ; for 

 liquid is capable of holding greater quantities of a gr 

 in solution, when under great pressure, than when tl 

 pressure is diminished. Hence a diminution of pressui 

 has the same effect as an increase of temperatur 

 Effervescing drinks, such as soda-water, champagn 

 beer, hold considerable quantities of carbonic acid : 

 solution. This gas is generated during fermentatio: 



