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FIEST TEAR SCIENCE 



nitrogen, neither burns nor supports combustion. Chem- 

 ists have found that these two gases are mixed in the air 

 in the proportion of about one part of oxygen to four parts 

 of nitrogen. 



Another heavy colorless gas called carbon dioxide is 

 found in the air in the proportion of about 3 parts to 

 10,000. There are in addition very small quantities of 

 several other gases, but these are not of sufficient impor- 

 tance to be studied here. Besides the gases, the air con- 

 tains other matter, such as water vapor, dust particles and 

 microbes. 



Experiment 58. Obtain four bottles of oxygen from the chemical 

 laboratory. If not obtainable, place a piece of sodium peroxide 

 . (oxone) about as large as the end of a finger 

 in a side necked test tube provided with a 

 medicine dropper filled with water, as shown in 

 Fig. 48. Put the end of the delivery tube 

 under the mouth of an inverted bottle filled 

 with water arranged on the shelf of a pneu- 

 matic trough. Drop water slowly on to the 

 sodium peroxide and collect the gas gener- 

 ated. Fill several bottles. Oxygen can also 

 be prepared by heating a mixture of about 

 one part manganese dioxide and two parts 

 potassium chlorate in a test tube and collect- 

 ing the gas over water (Fig. 49). Does the 



Fig. 48. 



Fig. 49. 



appearance of this gas differ in any way from air? Smell of it. 

 Has it any odor ? Into one of the bottles of oxygen insert a splinter 



