22 THE FORMS OP WATER IN 



Illustrative Experiments. 



65. I Lave said that when heated, air expands. II 

 you wish to verify this for yourself, proceed thus. Take 

 an empty flask, stop it by a cork ; pass through the cork 

 a narrow glass tube. By heating the tube in a spirit- 

 lamp you can bend it downwards, so that when the 

 flask is standing upright the open end of the narrow 

 tube may dip into water. Now cause the flame of 

 your spirit-lamp to play against the flask. The flame 

 heats the glass, the glass heats the air ; the air ex- 

 pands, is driven through the narrow tube, and issues 

 in a storm of bubbles from the water. 



66. Were the heated air unconfined, it would rise in 

 the heavier cold air. Allow a sunbeam or any other 

 intense light to fall upon a white wall or screen in a dark 

 room. Bring a heated poker, a candle, or a gas flame 

 underneath the beam. An ascending current rises from 

 the heated body through the beam, and the action 

 of the air upon the light is such as to render the 

 wreathing and waving of the current strikingly visible 

 upon the screen. When the air is hot enough, and there- 

 fore light enough, if entrapped in a paper bag it carries 

 the bag upwards, and you have the Fire-balloon. 



67. Fold two sheets of paper into two cones and 

 suspend them with their closed points upwards from 

 the end of a delicate balance. See that the cones 



