CHAPTER IV 

 Oxygen 



35. Occurrence. Oxygen is the most abundant element 

 in nature. About one-fourth of the air, by weight, is 

 free or uncombined oxygen. It enters into the composi- 

 tion of water, rocks, and minerals, and plant and animal 

 bodies. Seven-eighths of water and 



one-half of the solid crust of the 

 earth are oxygen in combination with 

 other elements. Oxygen is also 

 present in all animal and plant tis- 

 sue, making up a large portion of 

 the weight of these bodies. 



36. Preparation. Oxygen can 

 be prepared from a number of ma- 

 terials, as oxid of mercury, oxid of 

 iron, and potassium chlorate. When 

 made in small amounts in the lab- 

 oratory, it is usually prepared by 

 heating potassium chlorate, a com- 

 pound composed of the elements 

 potassium, chlorin, and oxygen. 

 The oxygen is separated by means 

 of heat, the process being as follows: 



Experiment i. Anneal the end of a 

 piece of glass tubing, 2 1/2 or 3 feet long. 

 Make a bend nearly at right angles to the Fig- 13- Delivery tube, 

 tube, about 3 inches from one end. Then make a second bend 

 of 2 1/2 or 3 inches on the opposite end of the tube nearly at right 



