22 LABORATORY EXERCISES 



ate and hydrogen peroxide into a small, wide-mouth bottle. 

 Use only a cardboard or glass cover. (See Fig. 18, Exercise 36.) 

 The oxygen simply expels the air. About 3 cu. cm. of potassium 

 permanganate is enough; the hydrogen peroxide can be added 

 a few cu. cm. at a time. In place of the potassium permangan- 

 ate you can use about 5 cu. cm. of manganese dioxide. Add 

 the hydrogen peroxide as already directed. 



c. In whatever way you prepare oxygen, put into a bottle of 

 it a small burning candle supported by a w r ire. Describe the 

 burning of the candle. Then remove the candle, and pour the 

 gas in the bottle into a test tube containing a little limewater. 

 Be sure you do not pour out any of the liquid (see Exercise 15). 

 Shake the limewater and the gas. What is the result? Com- 

 pare the product formed when the candle burns in oxygen with 

 that formed when it burns in air. What conclusion can you 

 draw from this fact? 



d. Put into the bottle in which oxygen is being formed a pine 

 splinter with a glowing (not a flaming) tip. What happens? 

 How could you tell a bottle of oxygen from one of air? 



Let the splinter burn for some time in the bottle of oxygen; 

 then test the gas in the bottle to see if it contains carbon dioxide. 

 Give your result. 



EXERCISE 18 

 AIR DISSOLVES IN WATER 



Apparatus and Materials. A water glass, fruit jar, pan of water, 

 burner or stove, pail of water, test tube, splinter. 



a. Fill a glass or bottle with fresh, cold water, and let it 

 stand in a warm place, near a stove or radiator, for an hour 

 or two. What collects on the sides of the dish? Where did 

 it come from? 



6. Fill a glass fruit jar entirely with fresh, cold faucet or well 

 water, cover the mouth of the jar with a wet paper (see Exer- 



