406 Mr Kleeman, On the Nature of the Internal Work 
molecular forces. This kinetic energy therefore represents available | 
energy, since it is evidently available for being converted into other 
forms of energy when the substance is in the perfectly gaseous | 
=U, | 
where V denotes the velocity of a molecule in the gaseous state | 
and m, its absolute mass. From the kinetic theory of gases we 
MV? 
2 
state. It follows therefore that at the critical point 
have Wi where m is the molecular weight of a molecule 
relative to that of a hydrogen molecule and R = 8-26 x 10’. Hence | 
at the critical point 
Ji iD os 
Wi (=~ ) LB iii (3) 
In a previous paper* I have shown that at the critical point 
Se) al 
U+u-—Uq= \r Gal. ~ Py TG Us docx eee (4), 
where v denotes the volume of a gram of substance. This 
equation was deduced from thermodynamics without introducing — 
any assumptions. It was also shown that according to the facts 
the right-hand side of the equation may be written m up 65. 
Thus the equation may be written 
Oyu =u, = ae i716. 2S eee ()} 
m 
since according to Young and Thoma’s law pu = — at the critical 
point. Equations (4) and (5) then give at once 
hee (= —) 2 = 113 Ue ee (6). 
m : 
It appears therefore that when a molecule passes from a substance 
into a less dense substance it absorbs heat in the latter substance 
on being bombarded by the surrounding molecules till 1t is intern- 
ally in equilibrium. The amount of heat absorbed is about 10°/, 
of the total. heat absorbed or energy spent in the transference of 
the molecule. The change in internal energy of the molecule is 
thus small in comparison with other energy changes as we might 
expect. 
As has been remarked before, it is of importance to obtain 
some definite information about the quantity w—u,. Thus I 
have shown in a previous paper} that if w—u, is small in com- 
parison with U the attraction between two molecules decreases 
* loc. cit., Sept. 1912, p. 395. 
+ Proc. Camb. Phil. Soc., xvi. Pt. 6, pp. 540—559 (1912). 
