472 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



given of the occasional absence of periodicity than the 

 specific heat, which can be plotted against the atomic weight 

 in the form of a rectangular hyperbola, or the atomic heat, 

 which gives a straight line parallel to the axis of atomic 

 weight. But this simple law ceases to hold at low tempera- 



Atomic Heat 



10 20 30 40 5O 60 70 



FIG. 



9O 1OO 



52. DEWAR'S ATOMIC 



tures. Thus the average values and average errors for 

 twenty-four elements from Mg to Bi (p. 365) are as follows : 



Temperature. Atomic heat. 



100 to 20C. 6'2o'2 



20 to -i88C 5-2 0-5 



- 195 to - 253C, 2-2 ro 



Dewar, to whom the measurements in the lowest range of 



