74 ANSWERS TO PRACTICAL QUESTIONS 



The weight of H from 2 grams of H 2 O is f gram. The 

 weight of O required to unite with it is 8xf, or - 1 /- giam. 



3O : 



48: 122.5 ::%-: x. 

 x = 4.537 grams. 



19. How much O would be required to oxidize the me- 

 tallic Cu which could be reduced from its oxide by passing 

 over it 9 when ivhite-hot 9 2O grams of H gas? 



The amount required to oxidize the Cu is obviously the 

 same as that which would be separated from the CaO by re- 

 duction. The number of grams of O thus separated must be 8 

 times the weight of the H, or 160 grams. 



20. How much O would be required to oxidize the me- 

 tallic Fe which could be reduced in the same manner by 1O 

 grams of H gas ? 



To oxidize 10 grams of H would require 80 grams of O. If 

 this be withdrawn from the oxide of iron, the same amount 

 would be required to oxidize the iron thus reduced. 



21. Why are rose-balloons so buoyant ? 



Because the H which they contain displaces air that is 

 more than 14 times as heavy. 



22. How much H must be burned to produce a ton of 

 water ? 



A ton is 2,000 pounds. The weight of H in a ton of watei 

 is $ x 2,000, or 222f pounds. To find the volume of this we re^ 

 member that the weight of 100 cubic inches of air is 31 grains 

 (see Popular Physics, p. 131). In every 5 parts of air there are 

 4 parts of 1ST, weighing 14 times as much as the same volume 



of H, and 1 part of O, weighing 16 times as much ; ~ -- 



o 



= 14.4, nearly. Hence, air is about 14.4 times as heavy as H. 

 Therefore 31 grains will be the weight of 100 x 14.4 cubic 



inches of H, or of ^-=~- Q of a cubic foot of H. To reduce the 



i, i ,00 



