180 WELLS'S NATURAL PHILOSOPHY. 



air in great part from tho interior, and on replacing it in an upriglit position, 

 the ink will be prevented from rising in the small tube and Ho wing over, on 

 account of the atmospheric pressure upon the exposed surface of tlie ink in 

 the small tube, which is much greater than the pressure of the column of 

 liquid in the interior of the vessel. As the ink in the small tube is consumed 

 by use, its surface will gradually fall ; a small bubble of air will enter and 

 rise to the top of the bottle, where it will exert an elastic pressure, which 

 causes the surface of the ink in the short tube to rise a little higher, and this 

 ©fleet will be repeated until all the ink in the bottle has been used. 



386k The peculiar gurgUug noise produced when liquid is 

 tittfe ^gurgle freely poured from a bottle, is produced by the pressure of the/ 

 •when a liquid atmosphere forcing air into the interior of the bottle. In the 

 ly out'ofitr^" fii'st 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 atmospheric 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. The bottle will 

 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 flov/ing 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 tlie upper part. The flow 

 being now continued and uninterrupted, no sound takes place. 



387. "Water, and most liquids exposed to the air, absorb a 

 ^iu^water ?^^* greater or less quantity of it, which is maintained in them by 



the pressure of the atmosphere acting on their surfaces. 

 Boiled water is fiat and insipid, because the agency of heat expels the air 

 which the water previously contained. Fishes and other marine animals 

 ,^ald not live in water deprived of air. 



The presence of air in water may be shown by placing a 

 presence of air tumbler containing this liquid under the receiver of an air- 

 ihown'^r'^ ^^ pump, and exliausting the air. The pressure of the air being 



removed from the surface of the water, minute bubbles will 

 ^ake their appearance in the whole mass of the water, and rising to the sur- 

 lace, escape. 



,-,_ , The reason that certain bottled liquors froth and sparkle 



why do some '■ ' 



tottlcd liquids when uncorked and poured into an open vessel is, that when 

 froth and spar- ^jj^y ^^^ bottled, the air confined under the cork is condensed, 

 and exerts upon the surface a pressure greater than that of 

 the atmosphere. This has the effect of holding, in combination with the 

 Jiquor, 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 

 condensation, 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 efisrvea- 

 cence and froth. 



