604 M. BIOT ON THE APPLICATION OF CIRCULAR POLARIZATION 
material systems, whether simple or compound, in which it exists; and 
I have positively and repeatedly said in the Annales d Histoire Natu- 
relle, that it was in this light that I regarded it*. In agreement with 
this view, in my applications of this character I have naturally had 
recourse to all auxiliary means suitable to be employed in conjunction 
with it. MM. Chevreul had no occasion to say, as he has done p. 592, 
that, “as M. Biot acknowledges,” when cane sugar and sugar of starch * 
are mixed together in one solution, it is necessary in order to distin- 
guish them to have recourse to alcoholic fermentation, or to the action 
of acids suitably regulated, in order to change the sum of the two ro- 
tations into a difference. He ought to have said that the employment 
of these auxiliary processes was my constant practice, and one of my 
principles formally expressed. 
The metaphysical question relative to the species being disposed of, 
I proceed to M. Chevreul’s other objections. The first three, which he 
ealls a, 6, c, consist of inquiries how, when a deviation to the left is 
observed, it is to be immediately ascertained whether it belongs to gum 
or to grape sugar not solidified, or to a mixture of the two substances, 
it being common to them both ; and when a deviation to the right is 
observed, how it is to be immediately distinguished whether it be pro- 
duced by dextrine or sugar of amidon. Considering these questions in 
the positive sense of their experimental application, it is not now ne- 
cessary in the actual state of optical chemistry to reply to them; for 
not only the particular conditions here suggested, but a great number 
of others analogous and more difficult, were long ago determined in 
my researches upon vegetation, in which the specialty of function of 
various organs, incessantly modified by the progress of life, effectuated 
mixtures very differently complicated than those suggested by M. 
Chevreul. As I cannot suppose that he is ignorant of these results, 
which were published in the Annals, and still less that he wilfully 
suppressed them, I must of necessity discover some abstract sense in 
the difficulties he has raised, independent of the real applications which 
I have made; and a word that I have just written, the word imme- 
diately, excites a suspicion in my mind upon the subject. In the title 
of my first memoir upon liquid grape sugar, which has since been fol- 
lowed by many other more extended applications of my methods, I have 
said that by means of the optical character derived from circular po- 
larization, the juices of fruits capable of producing sugar analogous to 
cane sugar, and those from which only grape sugar might be expected, 
may be immediately distinguished. In fact all the juices of our cli- 
* Vide the memoir upon the slow or sudden variations which occur in seve- 
ral organic combinations, Nouvelles Annales du Muséum d'Histoire Naturelle, 
vol. ii. p. 835. Ibid., vol. iii. p. 48, upon the application of circular polari- 
zation to the analysis of.the vegetation of the Graminez. [See p. 584.] 
q 
