( 682 ) 
this process is given out per molecular quantity of the second phasis. 
Or, if one prefers to reverse the process, it is the heat absorbed per 
molecular quantity of the second phasis if a homogeneous phasis is 
splitted up into two phases, — volume and temperature being kept 
constant, — provided the quantity of the second phasis is infinitely 
small compared with the quantity of the first phasis. 
We have proved l.c, that for substances, for which the attraction 
a 
may be reduced to a molecular pressure of the form =, as well in the 
Uv 
case that a is a function of the temperature, as in the case that 
a does not depend on the temperature, (é)), is certainly negative, 
and so that the energy increases, if in the process mentioned we 
make two separate phases form one homogeneous phasis. In the 
volume of the Arch. Néerl. dedicated to H. A. Lorentz [ have 
shown, by means of the calculation of the coefficient of compressi- 
bility, that the conclusions, deduced from the calculated value for 
(€9;)» for a simple substance (Cont. IT, pag. 104) namely 
(€o1)v = — v2 (K, + Ky — 2 Kjp) 
hold good. 
The conclusion, that the surface representing coexisting phases 
contracts at increasing temperature, which is only true for the case 
that (&)» is negative, is only in contradiction with the results of 
experiments for water at a temperature below 4°, nor will it hold 
good for diluted aqueous solutions at less than 4 degrees. For other 
substances, even for such as are known to be abnormal, as yet no 
deviations have been proved with certainty. I have pointed out I. c. 
that for associating substances a reason may be found tending to 
make the value of (1), positive. Yet the scarcity of the exception 
to the rule that (&))» is negative, has afterwards made me consider the 
question once more, whether the fact, that the mixture may be considered 
as a solution in a substance, consisting in the liquid state of molecules 
of greater complexity than in the gaseous state, is sufficient to 
account for the fact that: 
(fo) > 9, 
and the result of these more accurate considerations is, that in the 
case of the exception, — water below 4°, — other reasons as yet 
unknown must be present, and that the fact, that the solvent is an 
associating substance is not sufficient, to make (é91), from a negative 
to a positive quantity. 
Let us examine the process, for which (ej)» represents the decrease 
of the energy more closely. For a simple substance it may be 
thought to take place in two operations. In a certain volume we 
