TO CHEMICAL RESEARCHES, IN REPLY TO M. CHEVREUL. 605 
mates from which cane sugar has hitherto been extracted, those of 
beet-root, parsneps, carrots, and marsh-mallows, presented a rotation to 
the right, whilst all those which yield only grape sugar invariably 
presented a rotation to the left; thus by the word immediately I 
meant instantly, at the very moment; and indeed in my first ob- 
servations, I did not seek for other means of distinguishing the 
two kinds of sugar in question, not having at that period met with 
them naturally mixed sufficiently to conceal or intervert their 
proper rotation. Now if it be the word immediately which has 
shocked M. Chevreul, as expressing the pretence on my part of 
employing solely the optical character, to the exclusion of all other, 
and particularly of chemical means, I would beg him to observe that 
I have never acted in a manner to justify this interpretation. For even 
in my first fundamental memoir read before the Academy on the 5th 
of October, 1832, I determined the opposite rotations of the two prin- 
ciples of honey, the erystallizable and the uncrystallizable, after having 
separated them by means of alcohol; and I have never since neglected 
to seek all the assistance that chemistry is capable of affording. It is 
however; I repeat, with much hesitation that I attribute to M. Chevreul 
the suggestion of a difficulty which appears to me to be purely gram- 
matical ; for if such were his thought, he could not, without a degree 
of injustice of which I believe him incapable, cite my original expres- 
sions as he has done, without adding that all my researches subsequently 
published contradict the idea of exclusion which this interpretation at- 
tributes to me; and that I even formally expressed the contrary prin- 
ciple at the commencement of my memoir on the analysis of vegetation 
in the Graminez, as may easily be seen. As to the rest, it will at least 
be eyident from this discussion, that neither am I who have invented 
and applied the optical character, nor is M. Chevreul who examines it, 
of opinion that it should be separated from the chemical characters 
which may aid in its applications ; and this I apprehend is the only sci- 
entific point of interest at present. 
I now arrive at the last of M. Chevreul’s objections, objection d, 
which is expressed in these terms: “ Difficulty of estimating the quan- 
tity of an active principle from the density of the liquid by which it is 
held in solution.” I cannot possibly understand how, or in what re- 
spect this objection can be applied to my formule, or to the results 
which I have deduced from them. And certainly it is the intention of 
the writer so to apply it; for in his development of it, mentioning the 
necessity for distinguishing the proportion of the active substance in the 
solvent, in order to decide upon its specific nature, M. Chevreul im 
quires (p. 593.) how this proportion is to be ascertained ; and he adds 
“ it is, according to M. Biot, by taking the densities of the liquids,’ a 
method which appeared to him, and with truth, to be of difficult em- 
