OPTICAL 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 crystallize. When the benzene is 
completely volatilized, the immersion liquids 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 estabhshing the identity of a number 
of these substances. 
