CHAPTER IX 



COMMON SUBSTANCES 



SECTION I 

 ELEMENTS 



222. Oxygen. Oxygen is a gas without color or 

 odor ; it occurs most widely of all the elements. Many 

 salts and acids, and all bases, carbohydrates, and oxides 

 contain O. It is also a very important element in water, 



air, and the solid 

 earth. In the air 

 oxygen is free (not 

 combined with 

 other elements), 

 and it serves two 

 great purposes 

 it supports combus- 

 tion (burning) and 

 helps to support 

 animal life. We 



see its importance 



FIG 130 i 



at once when we 



know that without O in the air animals could not 

 live and common fires would not burn. 



Experiment 119. Fit a stopper to a large test tube. Perfo- 

 rate the stopper with a round file and push through this hole one 

 end of a glass tube, bent as in Fig. 130. Hang the whole on a 



192 



