321 



Note. In reference to the rotatory power of the cinchona alkaloids, 

 the calculation of the molecular rotation gives an excellent plan of 

 deciding on the purity of the alkaloid employed ; for if the absolute 

 molecular rotation be obtained precisely identical with those given 

 by other optical chemists, the purity may be inferred as proved. 

 But it is possible for a large quantity of two alkaloids to be present 

 in solution, one dextro-, the other levo- gyrate, and in such propor- 

 tions that the polariscope shall give no indication of the presence of 

 either. 



Thus a highly concentrated solution of the acid sulphate of quinine, 

 marking a left-handed rotation of 57*^, was mixed with rather more 

 than double its bulk of a similar solution of quinidin marking 24 t 

 The resultant solution gave no rotation at all, the one effect perfectly 

 neutralizing the other. 



In experimenting upon non-fluorescent solutions of quinine or qui- 

 nidin in the polariscope, it was found that these solutions were still 

 possessed of their original molecular rotation upon plane-polarized 

 light, even undiminished, if care were taken not to dilute the fluid 

 when destroying the fluorescence by the soluble chloride, &c., which 

 was always done by adding it in the solid state. 



XV. " Sur la Relation entre les Courauts induits et le Pouvoir 

 Moteur de 1'Electricite." By Professor CARLO MATTEUCCI 

 of Pisa. Communicated by W. R. GROVE, Esq. Received 

 May 20, 1858. 



Dans la l^ re partie de ces recherches j'ai etudie 1'influence des 

 extra-courants induits sur le fil menie de la spirale d'un electro- 

 aimant, sur les proprietes electro-magnetiques et electrolytiques du 

 courant qui met la spirale en action. Cette influence intervient ne- 

 cessairement dans le jeu des moteurs electro-magnetiques, et la re- 

 cherche de la correlation des forces presentee par un de ces moteurs 

 ne pourrait etre complete sans pouvoir determiner rigoureusement 

 la quantite d' action chimique qui a lieu dans la pile. Voici les re*- 

 sultats que j'ai etabli par des experiences exactes. 



1. Dans les experiences faites sans avoir les bobines de Pelectro- 

 aimant dans le circuit, la force electro-magnetique du courant est 



z2 



