EXPERIMENT 39. HEAT OF COMPRESSION 



Put a small compression or bicycle pump in a beaker of 

 water and, after taking the temperature of the water, move 

 the piston up and down about a hundred times. Again take 

 the temperature of the water, and from 

 your result state whether the compres- 

 sion of air in the pump had a heating or 

 cooling effect. 



A practical illustration of this is found 

 in the bicycle pump. As the air is 

 pumped into the tire the pump becomes 

 hot. This is due chiefly to the compres- 

 sion of the air inside it. The molecules 

 of which the air is composed are made to 

 move more rapidly when the piston is 

 pressed down upon them. As a result of 

 this they strike with greater force against 

 the sides of the pump and against each 



FIG. 36. The water is . L 



heated by the pump other and raise the temperature. 



EXPERIMENT 40. COLD OF EXPANSION 



Hold the bulb of a thermometer in front of the stop- 

 cock of a tank in which air has been compressed until it 

 occupies only one third of its original volume. Open the 

 stopcock and allow the air to expand, watching the ther- 

 mometer carefully during the process. Does the mercury 

 rise or fall ? Has the expansion of the gas, therefore, a 

 heating or cooling effect upon the gas ? 



A practical illustration of this principle is found in the 

 refrigerating rooms on our large ocean steamers. Air is 



