IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 321 
character which will distinguish this complex but fixed state 
will therefore be the same as for systems in single combination, 
or for simple mixtures, since it will be expressed by the con- 
stancy of the same function, whose absolute values can alone 
differ in these various systems and states. In consequence I 
shall call it, for the sake of shortness, the characteristic function 
of each system. 
22. I now consider the second phenomenal phase indicated in 
§ 19,—that in which the weight employed E of the inactive 
liquid is insufficient to saturate the weight P of the active sub- 
stance present. Then, in the fluid system supposed to result 
from their association, P forms with E chemical groups, homo- 
geneous or heterogeneous, which are, at least in part, incom- 
plete; so that any ulterior addition of the liquid EK changes the 
molecular state of the system. Among all the modes of internal 
constitution which may, abstractedly, result under this influence 
of unsatisfied affinities, I shall distinguish three which the ha- 
bitual experience of chemical reactions renders the most sup- 
posable, and I proceed to assign the optical characters which 
their progressive variations should present. 
23. We may conceive first that the liquid E is divided equally 
among all the constituent molecules of the active substance, so 
as to form with them as many identical and not saturated che- 
mical groups. Then the mixed system P + E being chemically 
homogeneous in all the states of non-saturation to which it may 
be progressively brought, the reasoning employed in § 8 becomes 
applicable to it for each of these successive proportions, If there- 
fore with the density 8 it produces the total deviation « on the 
plane of polarization of the type ray, when observed through the 
thickness /, the proper power [2], of the chemical groups 
composing it will be expressed by the formula 
a 
[4], = Ty 
Then, in proportion as the relative doses of the liquid E shall 
vary, still remaining below the point of saturation of P, the in- 
diyidual constitution of the mixed groups will vary; and with- 
out doubt their peculiar power [«], will likewise vary in conse- 
quence, since it could remain constant among such changes 
only by a special exception. But its variability, manifested by 
that of the relation 7 will be the only circumstance that can be 
