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 dHistoire 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. M. Chevreul had no occasion to say, as he has done p. 592, 

 that, " as 31. 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 

 calls a, b, 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 Mhich 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 \\'ere 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 ciiaracter 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 Museum d'Histoire Nalnrelle, 

 vol. ii. p. 3,'35. IbiJ., vol. iii. p. 48, upon tlie application of civcular polari- 

 zation to the analysis of the vegetation of the Graminea?. [Seep. 581.] 



