A YEAR IN SCIENCE 



65 



leave it exposed to the air for 48 hours. At the end of 

 that time examine the appearance of the surface of the 

 water. What does this indicate? What then forms a 

 part of the air? 



Does wood burn in the 

 air? What element does 

 this indicate to be present ? 

 How does the burning of 

 a pine splinter in the air 

 compare with the burning 

 in Exercise 31. part 4? 

 What does this indicate ? 



Pour water, of room 

 temperature, into the 

 pneumatic trough. On the 

 surface of the water float the evaporating dish con- 

 taining a piece of phosphorus, the size of a small pea. 

 Ignite the phorphorus and cover quickly with the bell 

 jar. What is the result? With what does the phos- 

 phorus unite in burning? When does it stop burning 

 in the jar? What are the white fumes? Leave the 

 experiment until these fumes have been dissolved ii? 

 the water. Does the water rise in the jar? What part 

 by volume does it occupy? This represents the 

 approximate proportion of oxygen in the air. 



Slip a glass plate over the mouth of the belljar and 

 invert it. Examine the gas. Has it color? Odor? Will 

 it support combustion? Does it burn? What is this 

 gas? (See Exercise 33.) Air is a mixture of gases of 



Fig. 23. 



