HEAT 



135 



is no air between the cork and the water. Now dip the flask 

 in warm water, and notice that the liquid gets larger and rises 

 up the tube. Take the flask out of the warm water, and see 

 that the coloured water gets smaller as it cools and that it 

 sinks in the tube. See Fig. 54. 



EXPT. 127. Procure a well-made paper bag and tightly tie 

 a piece of tape round the open end. Hold the bag in front of 

 the fire .and notice that the air inside gets larger and inflates 

 the bag. 



These experiments convince us that all bodies, whatever their 

 physical condition, solid, liquid, or gaseous, get larger when 

 heated and smaller when cooled. Now if they get larger their 

 volume increases, and as the amount of matter in them, i.e., 

 their mass, remains the same, 

 from what we have learnt 

 about density it is clear that it 

 must become less, or bodies 

 get lighter, bulk for bulk, ivhen 

 they are heated. The converse 

 holds true, if they get cooler 

 their density gets greater. 



Other Experiments to 

 Illustrate the Expansion 

 of Bodies when Heated. 

 EXPT. 128. Solder together 

 side by side a brass wire 

 and an iron wire, each about 

 two feet long. Hammer 

 the compound wire straight, 

 and notice how it bends 

 when heated. 



EXPT. 129. Fuse a piece 

 of platinum wire through 

 the side of a glass tube, 

 and notice that the glass 

 does not crack on cooling. 



The platinum and glass expand about the same amount for 

 a given increase of temperature. 



EXPT. 130. Fit with corks the necks of three 4 oz. flasks. 

 Fit tightly into the corks three narrow glass tubes open at 



Fig. 55. The Principle of the Air 

 Thermometer. 



