340 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT 
36. The turpentines which produce deviations of constant di- 
rection when liquefied by heat, and then restored by cooling to 
a viscous state, in which their sensible parts are almost deprived 
of relative movements, may also be presented as an example of 
bodies which exercise the rotatory power in the solid state; for 
the condensation which the cooling produces, increasing this 
power for an equal thickness rather than weakening it, it cannot 
be doubted that they would preserve it if they were submitted 
to an artificial temperature sufficiently low to solidify them com- 
pletely; and the natural temperature of our winters already 
suffices to harden them considerably without their action being 
destroyed or apparently weakened. These facts, and those still 
and the solution, having the density 6, is observed in a tube of the length J, 
where it produces in the red ray the deviation «. If [«]'- be called the mole- 
cular power of the primitive mass upon this same ray, and we make for the sake 
of abbreviation p 
— ; 
pte 
we haye, by the equation (2.) of § 14, 
[a]? = i coll 
led 
Now, by the experiments of inversion explained in the article cited in the 
Comptes Rendus, the portion S of the deviation # which is produced by the in- 
tervertible and consequently crystallizable sugar, which the mass experimented 
on contains, is determined. Then, designating by [«], the proper rotatory 
power of this sort of sugar, on the red ray,—a power previously determined by 
direct experiment,—the formule cited give 
— Sle)’ 
a [a |r " 
Let us imagine that the erystallizable sugar contained in the proposed mass is 
there solely united with inactive substances; then the observed deviation « 
being produced entirely by this kind of sugar, the experiments of inversion 
should give S = @; and, by this equality, they will prove that the circumstance 
in question takes place. We shall then have in such a case 
pape 
[alr 
I have stated that the preceding condition S = « was sensibly realized in the 
experiments of inversion which I made on plates of sugar decrystallized by 
heat. Admitting then that such was the case in the first experiment which I 
related, where the active mass had been prepared in the same manner, except- 
ing the more lively or more prolonged application of heat, the second expression 
of x will be applicable to it; and on introducing the numbers respectively given 
44°359 _ 0-81, that is to say, it should con- 
54°762 
tain ae in weight of unmodified crystallizable sugar, as I have stated in the 
x 
for [«]', and [c],, we deduce «= 
text. In fact, treating this mass by the process of refining, a considerable 
quantity of candy-sugar in crystals is obtained; but the exact proportion of 
this sugar could be appreciated only by the experiments of inversion, because 
in the operations employed to extract it materially, a considerable quantity is 
always lost, both by destruction and by mixture with non-crystallizable residues. 
