MICRO-ANALYSIS. 829 



chloride are added and the sections pushed to one side. The 

 hqiiid is allowed to evaporate and near the edge of the residue 

 branching groups of needles of caffeine gold chloride separate. 



Caffeine Gold Chloride. 



Orthorhombic : No axial ratio determinable. 



Forms observed: The three pinacoids (100), (010) and 

 (001). 



Habit : Tabular on the brachypinacoid, elongated on the c 

 axis with a ratio of length to width of 10: i or over. The 

 terminations of the rod are often more or less imperfectly 

 formed, perhaps from re-solution, the ends sometimes being 

 concave as in Fig. 159. but more often convex. 



Optical properties : The extinction is straight. The axis of 

 least refractive index is the long dimension of the crystal (fl^c). 



Pleochroism: fl pale lemon yellow. 



t somewhat darker yellow. 



Among the larger lath-shaped crystals of the caffeine gold 

 chloride there may be observed smaller, needle-like crystals, 

 resembling the former in color and pleochroism but sometimes 

 showing oblique extinction. Calling c the direction of elonga- 

 tion, the angle lAc = 30 approximately. 



The pleochroism is the same as in the larger lath-shaped 

 crystals, i.e.; 



^ pale lemon yellow. 



C somewhat darker yellow. 



The relationship between these two kinds of crystals is not 

 clear. It is possible that the larger crystals are a pseudosym- 

 metric modification of the second type; or again, the second 

 kind of crystal agrees so closely in habit and optical orientation 

 with caffeine, that it may be simply caffeine colored by absorption 

 of gold chloride, or of the double salt. 



Cocaine (Ci,H,,NOJ. 



Occurrence : See pp. 604-607. 



Cocaine (the methyl ester of benzoyl-ecgonin). At 25 C. 

 one part of cocaine is soluble in 600 parts of water; 5 parts of 



