828 BOTANY AND PHARMACOGNOSY. 



JMonoclinic ( ?) : No axial ratios obtainable. 



Fomis observed : The crystals are very fine needles and the 

 forms appearing cannot be identified. 



Optical properties : Certain of the crystals extinguish 

 straight, and others at a maximum angle of 313^, which would 

 indicate that the crystals are monoclinic and are observed in 

 different aspects. Calling c the direction of elongation of the 

 needles the orientation is: * ^/\c = i\\; CAc = 58^. Some of 

 the crystals show no complete extinction, as was also seen to be 

 the case with cocaine palladous chloride, and probably for the 

 same reason (see page 833). 



Caffeine Gold Chloride (CgHioN^Oo.HCl.AuCls + 2H2O). 



Solutions of caffeine give with gold chloride and some other 

 reagents crystalline precipitates. f To prepare caffeine gold 

 chloride the caffeine may be dissolved in distilled water, dilute 

 alcohol, absolute alcohol or a mixture of equal parts of absolute 

 alcohol and chloroform. One or two drops of the caffeine solu- 

 tion are placed upon a slide, to which is then added one or 

 two drops of an aqueous solution of gold chloride. The two 

 solutions are mixed by the use of a glass rod and then allowed 

 to crystallize. Crystals of caffeine gold chloride (Fig. 159) 

 are usually formed rather quickly, larger crystals being obtained 

 from the more dilute solutions of caffeine. The crystals are 

 also formed in solutions of caffeine acidulated with hydrochloric 

 acid. The microscopic crystals of caffeine gold chloride vary in 

 length from 0.4 mm. to 4 mm. They are said to be decomposed, 

 at least in part, on washing with either alcohol or water. The 

 Pharmacopoeia Helvetica gives the following micro-chemical test 

 for determining the presence of caffeine in cola: Transverse 

 sections of the cotyledons are placed in strong hydrochloric acid 

 and slightly heated ; then one or two drops of a solution of gold 



* Here a and C arc simply the axes of greatest and least refractive 

 index for the ohserved aspect of the crystal, and not necessarily the 

 greatest and least for the whole crystal. 



t Nicholson, Ann. Chcm. Phanii., 1847, 62, p. 71 ; and E. Schmidt, 

 Ibid., 1883, 217, p. 283. 



