Energy and Heat 129 



EXPERIMENT 42. Pour into a small flask enough 

 coloured water to cover the bottom of the flask to a 

 depth of half an inch. Fit the flask with a rubber 

 stopper through which passes a long glass tube as shown 

 in Fig. 37. The end of the tube should dip into the 

 liquid at the bottom of the flask. In this way the air 

 contained in the flask is cut off from the outside air. 

 Arrange a paper strip behind the tube as described in 

 the last experiment. Gently warm the flask and its 

 contents by placing the hand around the upper part of 

 the vessel. The coloured liquid . will be seen to rise 

 rapidly in the tube. This rapid movement indicates 

 that the air inside the flask has been largely increased 

 in bulk by the heat supplied by the warm hand. 

 The flask and the water have, of course, also gained 

 slightly in volume, but our previous work has been 

 sufficient to lead us to the conclusion that these 

 slight alterations, produced by the contact of the 

 hand, are not likely to account for the considerable 

 expansion that evidently occurs. 



If the air be displaced from the interior of the flask 

 by passing in coal-gas from the bench-supply for about 

 a minute, and the experiment be then repeated, it will 

 be found that the coal-gas also shows great gain in 

 bulk when heated in similar fashion. 



Summarising the observations made in the course of 

 the above experiments, we have 



(a) All bodies, whether solid, liquid, or gaseous, 

 expand when heated. 



(One rather important exception to this rule will 

 be dealt with fully in Chapter xvii.) 



(6) The expansion produced is most marked in 

 the case of gases, less with liquids, and least with 

 solids. 



H. D. S. 9 



