FUNDAMENTAL PROPERTIES OF THE. ELEMENTS RICHARDS. 213 



compressibilities of the solid elements as determined at Harvard; 

 these are immediately seen to be, like the atomic volumes, periodic 

 functions of the atomic weights. The parallelism can not but suggest 

 that atomic volume and compressibility are fundamentally connected ; 

 and, indeed, the theory of compressible atoms gives a plausible 

 explanation of the connection. We should expect the large atomic 

 volumes to be more compressible, because we might infer from their 

 bulk that they are not under as great pressures as the small volumes, 

 and material under slight pressure is likely to be easily compressible. 

 Moreover, the bulky and easily compressible elements are in most 

 cases more easily melted and volatilized than those possessing small 



t 



COMPARISON of ATOMIC VOLUMES 



JCOMPARISON of HEATS 

 \ OF FORMATION of 



L\ r CHLORIDES and 

 r^ 3 OXIDES 





Fig. 3. 



volume and slight compressibility. This is just what we might 

 expect; all these properties combine to indicate that the bukly 

 elements have less cohesion than the compact ones. 



Next, another set of waves may be considered, representing proper- 

 ties not often depicted in this way. These are the heats of formation 

 of sundry similar compounds, also plotted with relation to the atomic 

 weights. In the third curve are given the heats of combination of 

 chlorine with other elements, and below it a heavy line depicting 

 the heats of the combination of oxygen with these elements, both 

 sets of quantities being expressed in terms of gram-equivalents. 



