10 



HEAT 



more space, or to expand, and in some cases the expansion, 

 or increase in size, is surprisingly large. For example, if 

 100 pints of ice water is heated in a kettle, the 100 pints 

 will steadily expand until, at the boiling point, it will occupy 

 as much space as 104 pints of ice water. 



The expansion of water can be easily shown by heating 

 a 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 metal ball which when cool will 

 just slip through a ring (Fig. 2) 



FIG. i. As the J 



water becomes will, when heated, be too large to 



pa^ds'and rises sU P thr U S h the rin g' Telegraph 



in the narrow and telephone wires which in win- 

 ter are stretched taut from pole to 

 pole, sag in hot weather and are much too long. 

 In summer they are exposed to the fierce rays 

 of the sun, become strongly heated, and expand 

 sufficiently to sag. If the wires were stretched 

 taut in the summer, there would not be sufficient 

 leeway for the contraction which accompanies 

 cold weather, and in winter they would snap. 



Air expands greatly when heated (Fig. 3), 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 



FIG. 2. When 

 the ball is 

 heated, it be- 

 comes too large 

 to slip through 

 the ring. 



