( 707 ) 
dT 
dE =gq 7 
In this formula 7 represents the absolute temperature, Z the quan- 
tity of energy, transformed in consequence of the transition of the two 
systems into each other, and g a quantity of heat. If this transition is 
accompanied by chemical changes, then g is the quantity of heat 
which can be developed in maximo, per unity of mass, by this 
transition. 
As far as the present investigations reach this formula seems inde- 
pendent of the number of the component substances and independent 
of the configuration of the two systems which pass into one another. 
The form into which the chemical energy is transformed, is deter- 
mined by the nature of the transformer. 
Van ’r Horr himself considers this formula as the expression ot 
the second principal law of the mechanical theory of heat !). From 
this point of view its generality is clear, but it is no less clear that 
we have here an application of the law of entropy far beyond the 
limits for which the deduction of CrAusrus holds. In its application 
this formula has been chiefly restricted to approximately reversible 
processes in systems characterized by a point of transition. Therefore 
the limits within which this formula can be applied are not to be 
determined for the present. 
Jf the transitions are quite or partly irreversible, the sign of inequa- 
lity takes the place of the sign of equality. This makes the formula 
assume its more general form: 
dT 
If this transition takes place in consequence of variations of pressure, 
the same relation exists approximately between the quantity of trans- 
formed energy and the variation of pressure for the interval over 
which this change can take place. 
If on a receptive-organ of a reflex-apparatus a continuous stimulus 
acts, this stimulus will cause a change in the variables which 
determine the state of the chemical system. In consequence of these 
variations a displacement of equilibrium takes place. Equilibrium in 
the reflex-apparatus is only possible, when throughout the chemical 
system the pressure, the temperature and the thermodynamic potential 
for each of the independent variable components is uniform. Under 
influence, therefore, of the strain applied on a part of the system 
1) Van ’r Horr. lc. pag. 174. 
