OPTICAX, IDENTIFICATION OF ALKALOIDS. 9 



turned that two refractive indices which are not very dissimilar are 

 shown. When the stage is turned they, for the most part, become 

 dark when their long dimensions are nearly or quite parallel with one 

 of the cross hairs, although in some grains this extinction is not com- 

 plete in any position. When a high-power objective is inserted and 

 focused on a grain, the nicols remaining crossed, and the eyepiece is 

 removed, nearly every grain shows a portion of a biaxial interference 

 figure, colored rings, with one or two strongly curved dark bands 

 crossing them as the stage is revolved. In some cases the points of 

 emergence of both optic axes are in view simultaneously, and they 

 are fairly close together, showing that the axial angle is small. 



If it is desired to identify this substance in a drug mixture, the 

 alkaloid contents may be extracted with chloroform, dried, taken 

 up in benzene, and allowed to stand until the solvent is nearly 

 evaporated. Single large drops of the concentrated solution are 

 placed on several microscope slides, and immediately protected by 

 cover glasses. Evaporation takes place around the edge of the 

 covers, and there the alkaloids crystaUize. When the benzene is 

 completely volatilized, the immersion Uquids may be introduced, and 

 the appropriate observations made. 



SUMMARY. 



It seems reasonable to hope that optical-crystallographic measure- 

 ments will furnish a ready and certain means for the recognition of a 

 number of crystalline alkaloids, even when they are mixed in widely 

 divergent proportions. The observations made on such substances 

 with the apparatus and according to the methods described in this 

 bulletin were most successful in establishing the identity of a number 

 of these substances. 



