180 THE WEATHER 



has weight as truly as has water or stone or iron. About 

 1630, Galileo made the first attempt to find the weight of air. 

 He weighed a flask filled with air, then removed part of the 

 air by heating the flask just as we did in Ex. 35, Art. 131. 

 He sealed the flask while hot and then weighed it again. 

 Since this method removed but part of the air, he placed the 

 mouth of the inverted flask in water, unsealed it, and lowered 

 it as it filled with water. He 'then closed the mouth and 

 lifted the flask from the water. The volume of water re- 

 maining in the flask equaled the volume of air removed by 

 the heating. 



About 25 years later, Guericke constructed the first air 

 pump. After that, the air could be removed by the pump. 

 But no air pump will remove all of the air, and today when this 

 experiment is performed, we must find some means of dis- 

 covering how much air has been removed from the flask. 



Exercise 45. Weighing Air 



Fit a 2-qt. or 4-qt. bottle with a new one-hole rubber stopper 

 through which passes a short glass tube. To the glass tube attach 

 about 2 ft. of rubber tubing. 1 Fit the rubber tubing with a screw 

 clamp. Now weigh the bottle full of air with all attachments, using 

 trip scales (see Fig. 335). Attach the rubber tube to the air pump, 

 making sure that all joints are tight. Vaseline the joints if necessary. 

 Pump as much air as possible out of the bottle; close the rubber tube 

 tightly with the screw clamp; detach the tube from the pump and 

 quickly weigh the bottle and fittings. Place the tube and mouth 

 of the bottle under water and open the screw clamp. The bottle 

 quickly fills nearly full of water. Why? Hold the bottle so that 

 the water inside and outside is on a level. Close the tube and 

 lift the bottle from the water. Pour the water from the bottle into 

 a measuring graduate and record the volume. This volume is the 

 same as that of the air removed from the bottle. Compute the weight 

 of 1 liter, 1000 c.c., of air. 



A student performing this experiment obtained the following re- 

 sults (metric system) : 



1 Note: Thick- walled or pressure tubing should be used. 



