DYNAMICAL PRINCIPLES TO PHYSICAL PHENOMENA. 
505 
Making this substitution, the equation of equilibrium becomes 
0 
m iPi c i + - m s rc s + K (p + q — r) 
This equation may be written 
gp rfi 
y 
dw 1 
CQp + i~r e dS K0 
(53) 
(54) 
If the combination takes place without alteration in the number of molecules, 
P+ q = r. 
In this case the equilibrium state is independent of the volume of the vessel Q in 
which a given mass of gas is contained. 
If p -j- q > r, that is, if the number of molecules after combination is less than that 
before, + will increase with Q, so that rf/tp will be larger, the greater the value 
of Q, so that for a given quantity of the gases there will not be so much combination 
in a large vessel when the pressure is small as in a smaller one when the pressure is 
large. If, on the other hand, p + q < r, then the amount of chemical combination will 
be greater at low than at high pressures. 
We see from equation (54) that anything which affects the value of dco/dg will 
affect the amount of the combination which takes place ; anything which causes the 
potential energy to increase as chemical combination goes on, i.e., which tends to make 
dco/dg negative, increases, by equation (54), the value of yfj'Q', that is, it increases the 
ratio of the number of uncombined atoms to the combined ones, and so tends to stop 
the combination ; while, on the other hand, anything which makes the potential energy 
diminish as chemical combination goes on, since it tends to increase dcojdg, diminishes 
the ratio of the number of uncombined atoms to the number of combined ones, and 
so facilitates the combination. 
If we define the coefficient of affinity, co, of the gases A and B, to be the value of 
the steady state of 
JA , 
then 
dw 1 
co = CQ^ + r ~ > ' e~^ r ® ; . (55) 
and if the potential energy be increased by 8 co, the corresponding increment 8 co in the 
coefficient of affinity is given by the equation 
Sco 
1 d .ho 
K6 dg 
3 T 
MDCCCLXXXVIJ.—A. 
co 
(56) 
