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CHAPTER V 



THE CONSTITUTION OF MATTER 



41. In the previous chapters the words "solid", 

 "liquid", and "gas" have been used freely, and there 

 has probably been no difficulty in understanding what 

 was implied by these terms. It will be well, however, 

 to take into consideration the distinguishing features 

 of these three " states of matter " as they are generally 

 called and to deal with one or two important pro- 

 perties peculiar to those states, before proceeding 

 further. 



Our common knowledge and some simple experi- 

 ments will provide us with the necessary information 

 on which to base clear ideas of what is meant by each 

 of the above terms. 



We all know that a solid body does not require the 

 support of a containing vessel in order to maintain its 

 shape, and that, unless the body is acted upon by some 

 external force, it retains its size and shape indefinitely. 

 It may be readily believed that, if a penny and a written 

 description of its shape and size be sealed up in a glass 

 vessel, an investigator examining it a thousand years 

 hence would find that the description still held good. 



Thus our first point with respect to the nature of 

 solids is that they possess shapes and sizes which are 

 only changed by the application of force. 



EXPERIMENT 22. The spring of a spring-balance is 

 another example of a solid body. It has a definite 

 shape when the balance is not in use. Examine the 

 spring of such a balance and describe its shape. Hang 



