WATER 



83 



can only be the case if all atoms, no matter 

 of what element, require a constant amount of 

 heat to raise their temperatures one degree. 

 That is to say, in all elementary substances 

 the heat capacity of the atom is constant, and 

 independent of the nature of the element 

 (with the qualifications above noted). 



The study of compounds has shown that 

 this same generalization is also true of them. 

 This means that in all substances the heat 

 capacity of every atom is nearly constant and 

 is independent of its nature and of that of the 

 compound in which it finds itself. 



Accordingly the law of Dulong and Petit 

 may be formulated as follows ; — the specific 

 heat of a substance multiplied by the average 

 of the atomic weights of all the constitutent 

 atoms in the molecule is often equal to about 

 6.4, and is always not very different from this 

 number. This conclusion may be tested with 

 the data above recorded. 



