SCIENCE OF COMMON THINGS. 73 



Why a jug gurgles. Air in water. 



muscular action compress the air contained in them, 

 and give to it by compression a greater elasticity than 

 the air without. By the excess of the elasticity it is 

 propelled, and escapes by the mouth and nose. 



453 Why does a bottle or jug gurgle when liquid is freely poured 

 from it ? 



On account of the pressure of the atmosphere forcing 

 air into the interior of the bottle. In the first instance, 

 the neck of the bottle is filled with liquid, so as to stop 

 the admission of air. When a part has flowed out, and 

 an empty space is formed within the bottle, the atmo- 

 spheric pressure forces in a bubble of air through the 

 liquid in the neck, which, by rushing suddenly into the 

 interior of the bottle, produces the sound. . 



454 How long will a lottle continue to gurgle ? 



/So long as the neck continues to be choked with liquid. 

 But as the contents of the bottle are discharged, the - 

 liquid, in flowing out, only partially fills the neck ; and, 

 while a stream passes out through the lower half of the 

 neck, a stream of air passes in through the upper part. 

 The flow being now continued and uninterrupted, no 

 sound takes place. 



455 Does air exist in water f 



Water, and most liquids exposed to the air, absorb a 

 greater or less quantity r , which is maintained in them by 

 the pressure of the atmosphere acting on the surface. 



456 Why is boiled water flat and insipid f 



Because the agency of the heat expels the &ir which 

 the water previously contained. 



457* Could fishes and other marine animals live in water deprived of 

 air ? 



They could not, as they breathe the air contained in 

 the water. 



458 Why do ale, porter, and cider froth, and champagne sparkle, when 

 uncorked and poured into an open vessel f 



When these liquors are bottled, the air confined 

 under the cork is condensed, and exerts upon the sur- 

 face a pressure greater than that of the atmosphere. 



