50 



AIR AND FIRE 



when heated, and foams, or "effervesces," as the oxygen 

 passes off. If a small amount of iron oxide (rust) is mixed 

 with the potassium chlorate when it is heated, it gives off 



its oxygen more easily. 

 The substance manga- 

 nese dioxide, a black 

 the same effect. 



The apparatus required for 

 making oxygen is shown in 

 Fig. 43. A test tube contains 



The Common Way^f Preparing Oxygen. the mixture of powdered po- 



tassium chlorate and manga- 

 nese dioxide. The delivery tube is attached "gas tight" to the test 

 tube by means of a rubber stopper. The test tube is then heated 

 with a very small flame, and the oxygen given off is collected over 

 water in the bottle. When the bottle is full of oxygen, it is stoppered, 

 or covered with a glass plate, and set, right side up, on the table. 



A still easier methdtTof rnak- 

 ing oxygen is to let a solution of 

 hydrogen peroxide drop into a 

 flask (Fig. 44) upon some crys- 

 tals of potassium permanganate 

 just covered with water. 



51. Properties of Oxy- 

 gen. With the bottles of 

 oxygen made as directed 

 in 50 we can study the 

 properties of oxygen. 





Potassium Permanganate 



and 

 Dilute Sulphuric Acid 



FIG. 44. 

 Another Way of Preparing Oxygen. 



(1) In the first place, we can 

 test a bottle with a glowing splinter (the test used by Priestley). 



(2) Iron does not burnreadily in air, but it burns in oxygen. This 

 may be shown as follows (Fig. 45) : 



