Heat as a Quantity 177 



of this air, pour out the water left in the flask into a 

 small measuring cylinder and observe its volume. Next 

 fill the flask to the level of the bottom edge of the 

 stopper with water, and pour this water into a larger 

 measuring vessel. The volume of the water thus 

 poured out, minus that of the water left in the flask, 

 is the volume of the air which passed into the flask. 

 The specific gravity of air may be found by dividing 

 the weight of the air by the weight of the corresponding 

 volume of water, as previously explained. 



Knowing the specific gravity of air, we may deter- 

 mine those of other gases by filling a vessel of known 

 capacity with the gas whose specific gravity is desired, 

 weighing it, and also weighing the same vessel filled 

 with air. As an example of this, find the specific 

 gravity of carbon dioxide as in the following experi- 

 ment. 



EXPERIMENT 62. Find the volume of a flask as 

 indicated in the previous experiment. Weigh the flask, 

 which should be quite clean and dry, a well-fitting 

 cork being placed in the neck. Fill the flask with 

 carbon dioxide by passing the gas from a generator 

 (see Fig. 98) in which the materials used are marble 

 and hydrochloric acid. The gas should be dried by 

 passage through a drying tube containing calcium 

 chloride before it is allowed to enter the flask. The 

 flask should be maintained in an upright position, and 

 the gas should be passed in for at least 10 minutes 

 in a steady stream with the end of the delivery tube 

 almost touching the bottom of the flask. Slowly with- 

 draw the delivery tube while the gas is still issuing from 

 it, and re-cork the flask. Weigh flask and gas carefully. 



Subtract the weight of the flask filled with air 

 from its weight when filled with carbon dioxide. The 



H. D. s. ]2 



