SEPTEMBER 3, 1897. ] 
Of the two bodies which have been tested 
throughout long pressure intervals, naph- 
thalene shows a linear melting point and 
pressure ratio for 2,000 atmospheres, while 
the carbon tetrachloride of Amagat, though 
initially concave upward, soon also becomes 
linear. Clarence King has, therefore, in geo- 
logical considerations so represented it. To 
conform with Tammann’s inferences the in- 
terior of the earth would have to be a fluid. 
One point of issue, however, in these 
cases is clear: At Andrews’ critical tem- 
perature both the difference of specific vol- 
umes and the latent heat of fusion vanish 
simultaneously wherever observed. Under 
corresponding conditions of change from 
liquid to solid the internal pressures are of 
tremendously greater value for both states, 
and the passage of the solid into the liquid 
molecule may involve an immense transfer 
of energy without any corresponding change 
of volume, for the density of the molecule 
itself eludes observation. The manner of 
this isothermal change from one state to 
the next is in all cases along the character- 
istic doubly-inflected contour first pointed 
out by Thomson for vapors, and since elab- 
orated by Van der Waals, Clausius and 
others. We may, for brevity, call this a 
volume lag and measure it in terms of the 
pressure or the volume interval subtended. 
The liquid can exist even above the critical 
temperature, which would mean that even 
here pressure must be reduced below the 
critical pressure in order to rupture the 
liquid molecule. 
Pronounced as these phenomena are for 
the change from gas to liquid, they become 
much more remarkable, indeed often formi- 
dable, for the change from liquid to solid. In 
this case a volume lag subtending more 
than 100 atmospheres isthe rule. In other 
words, it takes much greater pressure to 
solidify a liquid at a given temperature 
than to liquefy the solid. Among all these 
cases there is a group of well-known bodies 
SCIENCE. 300 
in which, while the solidification pressure 
is of marked intensity, the isothermal pres- 
sure of spontaneous fusion may even be be- 
low zero or be in the region of negative 
pressure. Take the single example of 
thymol among many: This body between 
zero Centigrade and its melting point at 
53° can be kept in either the solid or the 
liquid state of pleasure. Given at about 
50° in the liquid state it would require 
more than 2,000 atmospheres to solidify it. 
If solid it must obviously remain so even 
if pressure be wholly removed. But thymol 
may be similarly treated beginning with 
the undercooled liquid state at 28°, 7. ¢., 
25° below its melting point. Hven here at 
least one thousand atmospheres are needed 
to condense it (400 have been tried quite 
ineffectively). Once solid it would require 
about 1,000 atmospheres of negative external 
pressure again to melt it. In other words, 
it could not be melted again on the same 
isothermal. 
If we but knew more about the physical 
constants involved in these transformations 
we could predict the results along the lines 
of J. W. Gibbs’ splendid theory of the 
equilibrium of heterogeneous mixtures; but, 
with the dearth of our concrete knowledge 
of long range physical phenomena relating 
to liquids and solids, we must be content 
with humbler methods. 
I have always regarded the significant 
behavior instanced for the case of thymol 
as capable of a broad interpretation. Pro- 
fessors J. J. Thomson and Fitzgerald 
abroad, and Elihu Thomson in this country, 
have recently sought for atomic dissociation 
in the electrolyzed vacuum of a Crookes’ 
tube. Speaking to the same point, I would 
venture to assert that we may reasonably 
look to the volume lag for a rational account 
of the genesis of atoms. We have already 
met with two orders of volume lag: the 
first at the mergence of gas into liquid being 
usually a few atmospheres in isothermal 
