84 NATURE STUDY 



the flask with the flame of the lamp. As the bubbles of air 

 escape have the children observe what happens and explain. Cool 

 the flask. Repeat the experiment several times; or better, allow 

 the children to repeat it. 



See how sensitive the air is to even a small amount of heat. 

 Arrange flask and tube so that the mouth of the tube is covered 

 with water, having driven out enough air so that the water will 

 rise well up in the tube. Place the hand or just one or two Ali- 

 gers on the flask and observe the change of volume. 



Arrange the flask and tube in a horizontal position. Get a 

 little water in about the middle of the tube. It is better to have 

 it colored with ink or some other coloring matter; this will enable 

 its motions to be more plainly seen. Repeat the experiments with 

 this apparatus. It will be very sensitive to small amounts of heat. 



In addition to these experiments, which are to be examined 

 very closely and seen clearly till they are well understood, many 

 other illustrations of the fact that heat expands air may be 

 devised by both the pupils and teacher. For example, a football 

 or a bladder partly blown up, then heated, fills out by expansion 

 of the contained air. 



The flask and tube with a paper scale may be used as an air 

 thermometer. For this purpose support the flask so that it stands 

 perpendicularly with the mouth of the tube immersed in water, 

 with the water rising a little way up in the tube. Or support the 

 whole in a horizontal position, putting a drop of liquid in the 

 tube. In the latter case a drop of water can not be used, as it 

 will evaporate. Use a small tube and a drop of strong sulphuric 

 acid or a drop of mercury. 



What makes the best thermometer of the substances thus far 

 used? Why? Give time for discussion and comparative experi- 

 ments. 



