52 



ELASTICITY OF AIR. 



Fig. 7. 



cave, and when the air is sufficiently rarefied within the receiver, the pressure 

 on the bladder will burst it, producing a loud noise like the discharge of a 

 pistol. Again, if a large glass bowl, having a bladder tied firmly on its mouth so 

 as to be perfectly air-tight, be placed under the receiver of the air-pump, on with- 

 drawing the air, the elastic force of the air confined in the bowl being still un- 

 diminished, and being no longer balanced by the atmospheric pressure on the 

 outside, the bladder will be blown into a convex form, and when the air in the 

 receiver is so rarefied that the elasticity of the air confined in the bowl suffers 

 little resistance, the bladder will burst, and the air confined in the bowl will 

 expand through the receiver. 



Fruit, when dried and shrivelled, contains within it particles of air, which 

 are held in its pores by the pressure of the external atmosphere. If, therefore, 

 this pressure be removed, we may expect that the air thus confined will ex- 

 pand, and if there is no aperture in the skin of the fruit for its escape, it will 

 distend the skin. Fruit, in this case, placed under a receiver, will assume the 

 appearance of ripeness, by exhausting the air ; for the expansion of the air 

 contained in the fruit, by inflating the skin, will give it a fresh, ripe appear- 

 ance. Thus a shrivelled apple will appear to grow suddenly ripe and fresh, 

 and a bunch of raisins will be converted into a bunch of ripe grapes. 



A flaccid bladder closed so as to be air-tight at the mouth, contains within it 

 a small portion of air. This air presses, by its elasticity, on the inner surface, 

 which is resisted by the atmospheric pressure from without. If such a bladder 

 be placed under the receiver of a pump, and the air exhausted, the external 

 pressure being thus removed, the elasticity of the air included will cause the 

 bladder to swell, and it will take all the appearance of being fully inflated. 



