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 
| 
7 
t COMPARISON of ATOMIC VOLUMES : 
( 
E ; 
=| K and 50 
= 
K COMPRESSIBILITIES 
z | 
E Na 0, 
mu 7 ; 0 
a aM is if 10 
= [er -— : ; 
S %IC Seen Ni shat oe an d sae 
ATOMIC 100 
COMPARISON of HEATS 
OF FORMATION of 
‘AC CHLORIDES and 
invig i ~ OXIDES 
Ba 
HEATS OF FORMATION 
Fia. 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. 
