XVIII 



THE CLASSIFICATION OF THE ELEMENTS 473 



temperatures are due, points out that " when plotted in terms 

 of their atomic weights, they reveal definitely a periodic 

 variation resembling generally the well-known Lothar Meyer 

 atomic volume curve for the solid state " (froc. Roy. Soc., 

 1913, A., 89, 167). The striking character of this resem- 



Atomic Volume 



VI 



VII d 



,U-. 



Q40 



R AX~EARTH' E -r*; 



HE 





24O 



140 150 160 170 



'URVE OK ATOMIC VOLUMES. 



180 19O 2OO 21O 



22O 23O 



blance is well shown in Fig. 52, above. The similarity 

 of the two curves suggests that, at low temperatures, 

 equal volumes of different elements have the same 

 heat capacity, instead of equal numbers of atoms, as re- 

 quired at higher temperatures by the law of Dulong and 

 Petit. 



Correction of atomic weights, (a) Valencies corrected 

 or confirmed. When the equivalent of a metal has been 



