Put a mouse—it is necessary to catch him first—into the receiver, and work the pump. Soon the animal will show all the signs of being choked, and eventually will die. This is proof sufficient that animals cannot live without air.
Balloon in Vacuum.
Place in the receiver a small bladder, such as are sold in the streets for a few cents. Wet it a little to make it more supple. Now, in the ordinary way the air inside the bladder exerts the same pressure on the skin of the bladder as does the air on the outside. Now work the pedal so that the air in the receiver is gradually exhausted. The bladder will be seen to gradually swell and finally burst. It bursts because as the air in the receiver is exhausted by the pump, the air outside the bladder exerts a less force than the air inside. But the air inside is confined by the bladder skin, a not very strong material, as you know, so as soon as the difference between the inside and outside pressures is greater than the strength of the bladder, the latter bursts. This experiment also shows the expansible power of air.
Boiling Cold Water.
Place in the receiver a tumbler of cold water and work the pump as before. In a few minutes, as soon as the air is sufficiently exhausted, the water will apparently boil. Yet you know the water does not boil in a kettle unless heated to 212 degrees. This phenomenon is thus explained: The vacuum causes the air-bubbles contained in the water to escape. They easily do so, because there is scarcely any reserve on the surface of the liquid (see fig.).
