IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 881 
to that of the tartaric acid. It was almost rectilinear in the 
series where this proportion was nearly equal. Now, from what 
has been established in § 59 of the preceding section, this rela- 
tion of equality was precisely that which gave to the group of 
tartaric acid and water its maximum of optical energy, at the 
temperature at which its combinations with the boracic acid 
were observed. 
66. In the detailed table of each series I have, for brevity 
sake, called the quantity [«], or the specific rotatory power 
a 
4 
of the tartaric acid, and I have expressed its values for a 
length of 100 millimetres, as they are inferred from the hyper- 
bolic law, taking into consideration the corresponding values 
given by observation. The mean difference of these two modes 
of evaluation is inappreciable. The preceding denomination of 
[«] applies to the tartaric acid alone the specific power actually 
exercised by any molecular group, which it forms with the two 
other elements of each solution. If it were desired to apply 
this denomination to the mixed group composed of water and 
of this acid which is supposed to combine with the boracic 
acid without decomposition, there would only result a propor- 
tional change in the absolute numerical values ; but the physical 
law expressing their mutual dependence would remain the same. 
In fact, applying here the reasoning in § 20 of the first section, 
. let [«]' be the actual molecular power of the group thus com- 
posed, when it has entered into combination with the boracic 
acid, and let us call («)’ its ponderable proportion in each unit 
of weight of the total system. We shall first have 
(si =e+e; 
(«)! = (n =P 1) &. 
Now, if this group forms part of a system whose density is 8, 
and if it introduces into it the resulting power [«]! attributed 
to it, it will produce Pale the thickness J a total deviation 
expressed by [a]! 72 (<)', or (x + 1) [a]'Ze%. Then, if the devia- 
tion really observed is a, we conclude 
(m + 1) [a]'= 
Led’ 
and since we have made 
or, since € = ne, 
a 
Soma rE 3 
there will result 
(n +1) [a]! = [a]. 
