736 Sir J. J. Thomson on the Application of the 



but if k is the bulk modulus this work is equal for unit 

 volume to 



, 7 3-65 Ne 2 

 nence fc-— — = — , 



w 



here N is the number of atoms per unit volume. 

 If M is the mass of an atom and A the density, 



M = A and N(d) 3 = l, 



hence ^ == ~1T (m) ( ^ 



The comparison of the values for k given by (8) for the 

 monovalent alkali metals with their values as determined by 

 Richards' very' valuable experiments (Kaye and Laby's 

 Tables) is given in the following table : — 



Metal. A. M/l-64 X 10- 24 . h calculated. h observed. 



Lithium -534 7 '14 X 10 12 -114 xlO 12 



Sodium -971 23 -068 x 10 12 '065 x 10 12 



Potassium . . . '862 37 -03 x 10 12 '032 x 10 1 * 



Rubidium . . . 1532 85*5 '022 x 10 15 '025 x 10 12 



Caesium 1'87 132 '016 x 10 12 '016 x 10 12 



Thus the absolute values of h and not merely the relative 

 ones are in very close agreement. 



If we take the cell with charges 1/8 at its corners and the 

 atom at its centre as the unit, the potential energy corre- 

 sponding to each cell is — l'82e 2 /d. When the solid is 

 changed into a monatomic gas, each of these cells becomes 

 an atom whose energy is — \ e 2 /c. Thus to convert N atoms 

 of a monovalent solid into a monatomic gas requires the 

 expenditure of 



units of work, or, if 2c/c?=l*7, 



=N^ 2 



1^4 



d ' 



If N is the number of atoms in a gramme NM = 1, and 

 d z = M/ A ; hence the work required to convert 1 gramme of 



