6 LABORATORY EXERCISES. 



delivery-tube and remove the glass 

 cover. 



a. Why does the bottle remain filled 



with water? (See experiment 4.) 



b. Continue to heat slowly the mixture 



in the test-tube. What do you 

 observe? Does oxygen dissolve 

 readily in water? How do you 

 know? 



3. When the escaping oxygen has filled the 

 bottle, cover it with the glass plate, re- 

 move it from the tray, and turn it right 

 side up. Fill the other bottles in the 

 same way. Why is the glass cover 

 placed over each bottle? 



FIG. 



To obtain pure oxygen the gas should be 

 run through two bottles as shown in Fig. 

 i. Place in the first water, and in the 

 second a solution of caustic soda. These 

 liquids absorb most impurities. When 

 the oxygen has been washed in this way, 



