HEAT 



flask (Fig. i) filled with water and closed by a cork 

 through which a narrow tube passes. As the 

 water is heated, it expands and forces its way up 

 the narrow tube. If the heat is removed, the 

 liquid cools, contracts, and slowly falls in the 

 tube, resuming in time its original size or volume. 

 A similar observation can be made with alcohol, 

 mercury, or any other convenient liquid. 



Not only liquids are affected by heat and cold, 

 but solids also are subject to similar changes. A 



FIG. i. As the me tal ball which when cool just slips through a 

 water becomes r & 



warmer, it ex- ring is, when heated, too large to slip through the 



pandsand rises f - Telegraph and telephone wires in winter 



in the narrow 6 



tube. are stretched taut from pole to pole. In summer, 



when they are exposed to the fierce rays of the 

 sun, they expand and sag until they are much too long. If the 

 wires were stretched taut in the summer, there would not be 

 sufficient leeway for the contraction which accompanies cold 

 weather, and they would snap under the strain. 



Air expands greatly when heated (Fig. 2), but since air is 

 practically invisible, we are not 

 ordinarily conscious of any change 

 in it. The expansion of air can be 

 readily shown by putting a drop 

 of ink in a thin glass tube, inserting 

 the tube in the cork of a flask, and 

 applying heat to the flask (Fig. 3). 

 The ink is forced up the tube by the 

 expanding air. Even the warmth 

 of the hand is generally sufficient to 

 cause the drop to rise steadily in 

 the tube. The rise of the drop of 

 ink shows that the air in the flask form of bubbles. 



