Minor Constituents of Air 



245 



EXPERIMENT 105. Fill a flask of about 1 litre in 

 capacity with water. Push in, with a screwing motion, 

 a tight-fitting rubber stopper, carrying a bent delivery- 

 tube as shown in Fig. 79. Pushing in the stopper 

 should result in filling the delivery-tube with some of 

 the water from the flask. The upper end of the tube 

 should be flush with the bottom of the stopper. Insert 

 the free end of the tube under the mouth of the gradu- 

 ated vessel, which may well be a 100 c.c. measuring 

 tube or cylinder. Heat the water to boiling-point. 

 Bubbles of gas will be formed as the liquid becomes hot, 



Fig. 79. 



and these will rise to the top of the flask, escaping 

 later via the tube into the collecting vessel. Continue 

 the heating for about ten minutes after the water has 

 reached boiling-point. At this stage remove the 

 measuring tube to another part of the trough and then 

 turn out the burner. Observe carefully what happens 

 as the water in the flask cools. 



Exercise for Student. 

 Account for all observations made as the water cools. 



