.102 



GENERAL SCIENCE 



with water. Add a small amount of red ink to the water in the 

 student's lamp chimney. Heat the water in the flask. 



Why does the colored water run down the straight tube into the 

 flask? Why does the uncolored water in flask rise in the crooked 

 tube to the student's lamp chimney? 



Why Air Carries Heat. One cubic foot of air weighs 0.07203 

 pound or 504 grains. For every five degrees the air is heated it 

 weighs between 4 and 5 grains less; hence, the heated air, being 



lighter than the cold air, will rise 

 and float above the cold air, while 

 the cold air, being heavier, will 

 sink. 



Experiment to Show the Con- 

 vection of Air. Arrange two chim- 

 neys over holes cut in the sides of 

 a chalk box. Stand the box on 

 the opposite side and substitute 

 a piece of glass for the cover. 

 Place under one chimney a candle. 

 Hold over the other chimney a 

 piece of Chinese joss stick, or a 

 piece of touchpaper made by 

 soaking the paper in a saturated 



solution of saltpeter. Why will the smoke go down the chimney? 

 Why is the smoke soon seen coming out of the other chimney? 

 Why will the smoke not go down the chimney which has the 

 candle burning under it? 



The table on page 103 will be found useful in determining the 

 weight of the atmosphere of any room. For example, suppose the 

 room is 10 feet wide by 20 feet long by 15 feet high; the room will 

 hold 3000 cubic feet of air. Suppose the barometric pressure is 30, 

 the relative humidity 60 per cent, and the temperature 65 F. 

 From the table, the weight of each cubic foot of air (dry) at 65 F. 

 is 0.07203. Since the barometric pressure is 30 it is neces- 

 sary to add one-half of 0.002530 or 0.001265. Also six times 

 0.000059 must be subtracted 'since the relative humidity is 60 

 per cent. 



FIG. 81. Is the smoke pushed or 

 pulled down the chimney? Why? 



