1333 : 
dlogv= — xdp 
dlogx 
v— v, =| trl, 
and if the coefficient is treated as independent of the temperature, 
dv d log x dk 
—=—| — }—*_ — 1x ‘ 
dT dp So NE 
If now @ is the density of the body, c the specific heat (the dif- 
ference between c and c‚ being considered as immaterial) expressed 
7 
in calories and A the mechanical equivalent of heat, we have = 
we have 
— Aecvv, and for the coefficient of cubical expansion 
1 dv d log x 
ee ee) eo, Se (16) 
a value that can well be positive, as the compressibility decreases 
with increasing pressure. 
§ 10. An example may teach us, whether this result agrees with 
observation, at least as to the order of magnitude. 
According to the measurements of LussaNa ') the compressibility 
of lead decreases by about 35 of its value when the pressure is 
raised to 1000 atmospheres. Therefore we have, taking the atmosphere 
as unit of pressure 
de RT 
dp 
and if p is expressed in dynes per cm? 
d log x ‘ 
BBD IL 
dp 
For the compressibility itself Lussana’s value is x = 3,9.10—?2, 
so that the coefficient of Ace in (18) becomes equal to 1,6.10-H. 
With A=4,18.10'; c=0,03 and o=11 we find a = 0,00022, while 
in reality the coefficient of expansion is 0,00008. 
For tin Lussana’s observations lead to the numbers 
d log x 
Se ae x= 4,110-P, 
dp 
Here c= 0,05 and o==7,3: This gives «a = 0,00027. The coeffi- 
cient of expansion is 0,00006. 
It is seen that the agreement is scarcely satisfactory. 
1) Taken from W. Scuut, Piëzochemie der gecondenseerde systemen, p. 72. 
Proefschrift, Utrecht, 1912. . 
É 85* 
