318 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT 
that which the primitive groups of the active substance would 
exert isolated, I designate by [«], the deviation which would be 
produced on the type ray, through the unit of thickness, by a 
diaphanous system composed solely of these new groups, and 
having an imaginary density 1 at the temperature at which the 
experiment is made. Returning then to the proposed system, 
since these groups are there uniformly diffused in .an inactive 
liquid, which is supposed to have no modifying action upon them, 
the reasoning in § 14 is applicable to them, that is to say, that 
the observed deviation « should be equal to the product [a], 2, 7@ 
under such circumstances. Establishing then this equation, sub- 
stituting for e, its value in «, and deducing [«],, we obtain 
[«],= (nb 1) les? ot 0" oat, Ae 
or P45) 
a ( 
i wy ae . . , (3.) 
The function (z + 1) [«], is therefore in this case absolutely of 
the same form as the function [a] of § 14; and, like it, it is 
composed entirely of observable quantities. Now, since the 
new-formed groups are supposed not to be modified by the 
indefinite addition of the superabundant portions of E, [«], 
ought to be constant by the identity of these active groups in 
all the similar systems in which E is in excess; and the multiple 
n ought likewise to be constant, by the fixity of their composi- 
tion, in these same systems. Therefore, if the numerical value 
of the function eke be calculated according to the ob- 
(n+ 1) [¢], = 
servable elements composing it, we ought always to find it the 
same in all the systems thus derived from one another by pro- 
gressive additions of KE, when the physical conditions supposed 
in the reasoning have been realized; that is to say, when the 
quantity of inactive liquid employed shall surpass or equal the 
quantity necessary to saturate the active substance present, in 
the sole kind of fixed combination which it is supposed to form 
with it. I include in this statement the case of equality which 
corresponds to exact saturation, because it is contained in the 
same formula. In fact, if the weight E of the inactive liquid is 
just sufficient to saturate P in the combination formed, E be-. 
comes equal to xP. Substituting this value of E in the equa- 
