INTERESTING THINGS ABOUT THE AIR 



15 



point of water and the 100 mark at the boiling point of 

 water. Because there are two scales, it is always necessary, 

 when we write temperatures, to indicate which scale is used, 

 and thus we say that the boiling point is at 100 C. or 212 F. 

 Since both types of thermometers are in use, it is important 

 to be familiar with both of them and to be 



fi\ 



able to determine the equivalent of a given 

 reading of one thermometer in terms of the 

 other type of thermometer. 



In the Fahrenheit scale the freezing 

 temperature is 32 above zero and the 

 boiling temperature is 212 above zero. 

 Therefore there are 180 between freezing 

 and boiling, according to the Fahrenheit 

 system. In the centigrade system the 

 freezing temperature is zero and the boil- 

 ing temperature is 100. Therefore 100 

 divisions on the centigrade scale equal 

 180 divisions on the Fahrenheit scale. 

 One centigrade degree equals 1.8 Fahren- 

 heit degrees. A temperature of 80 C. is 

 equivalent to 80 x 1.8 + 32, or 176 F. 



14. Some effects of expansion. It was 

 learned in a previous experiment that if 

 the air in a bottle is heated, the mouth 

 of the bottle remaining open, the air will 

 expand and some of it will escape. The 

 air that remains fills all the space that 

 the whole amount originally occupiec 



weigh the same, for only a part of the original air is in the 

 bottle, and a part cannot weigh as much as the whole. Care- 

 ful measurement and weighing will show that the weight of 

 the bottle is less by exactly the weight of the air which has 

 escaped. We usually express this by saying that heated air 

 is lighter than cold air. We must remember, however, that 



