AND AGRICULTURE. 



17 



by the miner. Hydrogen is one of the constitu- 

 ents of water. (See Appendix, 3.) 



Fig. 4. Fig. 5. 



OXYGEN is also a gas. A taper burns with 

 increased brilliancy in oxygen. It was at first 

 called vital air. It is heavier than hydrogen, 

 and heavier than the atmosphere. The air we 

 breathe contains one-fifth of its bulk of oxygen. 

 Its name means acid-maker. It combines with a 

 ^reat many substances, forming oxides : the rust 

 on iron is caused by oxidation, and most earths 

 are only metals in different degrees of oxidation. 

 Oxygen is one of the constituents of water. It 



Questions. Of what is hydrogen one of the constitu- 

 ents ? What is oxygen ? What first called ? Is it heavier 

 than the atmosphere ? How much oxygen does the atmos- 

 phere contain ? What are oxides ? Of what fluid is oxygen 

 one of the constituents ? 



2* 



