CHEMICAL MICROSCOPY 



solution to dryness, and testing the solid 

 hydrochloride of the volatile base with 

 HAuBr4 in H3PO4 . (Fig. 3a*) 



The crystalline hydrochloride of a volatile 

 amine can be examined microscopically be- 

 fore adding a reagent. If it is hygroscopic, 

 and so fails to dry and crystallize in open air, 



* See Fig. l,p. 53. 





•«• 



Fig. 3b. dZ-Methamphetamine with HAuBr4 in 

 H3PO4, (20).66X. 



it can be inverted over a cavity which con- 

 tains a drop of concentrated H2SO4 . Most of 

 these residues are not especially distinctive 

 in themselves, but as an exception, a mixture 

 of d- and c?Z-amphet amine (used by some 

 pharmaceutical manufacturers) leaves a hy- 

 drochloride residue altogether different from 

 that of either (i-amphetamine or rf^amphet- 

 amine alone. (Figs. 4a, b, c.) 



In general, the tests are observed for only 

 about two hours, although most of them can 

 bo allowed to stand much longer, preferably 

 with humidity controlled, and occasionally 

 with formation of valuable new test crystals. 



The chemical meaning of the tests is 

 noted: whether a test for a volatile amine is 

 obtained, and if so whether it is the origi- 

 nal compound or a decomposition product 

 (especially likely with a diphenol). With 

 phenols and diphenols the gold reagents give 

 crystals of metallic gold by reduction, which 

 when well-formed are hexagons and tri- 

 angles, blue-green by transmitted light. This 

 reduction may also be due to a double bond, 

 as with isometheptene, one of the sym- 

 pathomimetic drugs. 



The compounds are classified into four 

 groups : 



I. no test for a volatile base. 



Fig. 4a. Crystallization of d-amphetamine hydrochloride (volatility test), striate formation, 

 with crossed nicols. 66X. 



68 



