SCIENCE OF COMMON THINGS. 



Frothing of ale. Sparkling of champagne. Meteorology. 



This has the effect of holding, in combination with the 

 liquor, air or gas which, under the atmospheric pressure 

 only, would escape. If any air or gas rise from the 

 liquor after being bottled, it causes a still greater con- 

 densation, and an increased pressure above its surface. 

 When the cork is drawn from a bottle containing liquor 

 of this kind, the air fixed in the liquid, being released 

 from the pressure of the air which was condensed under 

 the cork, instantly makes its escape, and, rising in 

 bubbles, produces effervescence and froth. 



459 Why do bottles containing ale, cider, porter, &c., frequently 

 burst f 



It is the nature of these liquids to produce gas or air 

 in considerable quantities, the elastic force of which 

 sometimes becomes greater than the cohesive strength 

 of the particles of matter composing the bottle, which 

 then necessarily gives way, or bursts. 



460 Why does one kind of liquor froth, and another kind only sparkle, f 



Those liquors only which are viscid, glutinous, or 

 thick, froth, because they retain the little bubbles of 

 air as they rise ; while a thin liquor, like champagne, 

 suffers the bubbles to escape readily. 



CIIAPTEK VI. 



ATMOSPHERICAL PHENOMENA. 



461 What designation do we give to that department of science which 

 treats of the various phenomena of the atmosphere? 



Meteorology. 



463 How is the air heated f 



In two ways ; either by the rays of the sun passing 

 through it, or by the heat communicated to it by the 

 earth. 



