CHAPTER II. 



EXPANSION OF SOLIDS WITH RISE OF TEMPERATURE. 



Linear Expansion of Solids Ramsden's Method Modern Use of the Method 

 Method of Lavoisier and Laplace Results Fizeau's Optical Method Applica- 

 tions of Linear Expansion Volume Expansion of Solids. 



As a general rule bodies expand with rise of temperature. As a general 

 rule, also, gases expand more than liquids, and liquids more than solids. 

 As regards both liquids and gases, we have only to consider change of 

 volume, for fluid substances have no shape of their own ; but with solids 

 we have also to consider change of length as well as change of volume. 

 We shall first deal with the change of length of solids. 



Linear Expansion of Solids. Though the increase of length of 

 solids with an ordinary rise of temperature is small, it is still sufficiently 

 considerable in many cases to be of great practical importance. For 

 instance, in the construction of 

 railways it is necessary to leave 

 a small interval between the 

 rails to allow free play for 

 expansion of the iron. Iron 

 tubular bridges, again, have to 

 be fitted on rollers, so that on 

 expansion they may lengthen 

 freely. Iron water-pipes have 

 sometimes to be provided with 

 telescopic joints. In tubular 

 boilers, the fact that copper 



expands more than iron is made use of to secure water-tight joints. 

 The copper tubes are fitted into the iron end-plates when cold, and on 

 expansion they fit still more tightly, and so prevent leakage. Pendulum 

 clocks, especially with metal pendulum-rods, go appreciably slower in 

 summer than in winter, owing to the lengthening of the pendulum, 

 and the rate may easily change to the extent of one minute per 

 week. These examples all show the importance of an exact know- 

 ledge of expansion, while the last prepares us for the difficulty of the 

 investigation by showing us how small is the quantity to be measured. 

 A change of rate of one minute in a week is a change of 1 in 10,080, 

 which may be shown to correspond to a change in length of the pendulum 

 of 1 in 5000. 



The earliest attempt to measure linear expansions appears to have 

 been made by apparatus resembling in principle the well-known instru- 

 ment given in Fig. 9, the bar being placed against the short arm of the 

 lever L when cold, and again when hot, and the movement of the long 



FlG. 9. Expansion Apparatus. 



