No. 149.] 187 



TRANSLATION. 



[Communicated to the American Institute^ by H. Meigs, Esq.] 



RaspaiPs System of Organic Chemistry, on circular polarization^ 

 employed as a means of distinguishing chemical species. 



Biot's very interesting inquiry on this order of phenomena, 

 led to results that are incontestible. He says when a ray of light, 

 polarized by reflection, passes across a tube full of any liquid, if 

 it is viewed through a plate of tourmaline* placed perpendicu- 

 larly to the course of the ray, it is found that it deviates to the 

 right or left ot the position which it occupied when the tube was 

 empty; and then it is said that the liquid has turned the plane 

 of polarization to the right or left. (Polarization of light is a 

 modification of light after it has undergone certain reflections 

 and refractions, which, as is said, give poles to the ray like those 

 of a magnet, or sides with the opposite properties.) This deviation, 

 whether to the right or left, increases with the density of the 

 liquid and the thickness of its mass. This property, wliich was 

 first discovered of Quartz by Biot and Arago,was called by Biot 

 polarization by rotation^ and by Fresnel circular polarization. The 

 recent researches of Biot consist in the application of this law to 

 the determination of Organic species. It results from them that 

 the soluble substance of fecula (of the nature of starch) obtained 

 pure, turns the plane of polarization upwards and to the righfj 

 more than any other substance. That sugar, whether from the 

 cane, the beet, or the mallow, produces a like, but less deflection; 

 but that gum arable and grape sugar, from whatever plants ob- 

 tained, turn the plane of polarization to the left; but when these 

 are solidified they turn to the right.) and although agai?i made liquid^ 

 will never again turn it to the left. 



These results are justly deemed very interesting, and strongly 

 invite us to further research. 



* The most perfect form of Schorl, a black, prismatic, brittle crystal, becomes 

 electric by heat or friction, has much lustre. The ancients called it Lyncurium. Its 

 chief components are Silica and Alumina, with about ten per cent, of Soda and a 

 little Oxide of Manganese and Iron. The transparent colored varieties are some- 

 times made ornaments of rings, and this substance is valued on account of its im- 

 poj'tance in experimenting upon the polarization of light. 



