CHEMICAL MICKOSCOPY 



pent amine, nylidrin) respectively, with HAu- 

 CI4 in (1 + 2)H;,P04 , HaPt U in (2^ + 1) • 

 H3P()4 (minimum Nal), and 1.8 HAuBr4 iii 

 2H3P04-1(2 + 3)H2S04. Especially note- 

 worthy arc the "corkscrew" crystals of the 

 first mentioned. 



HAuBr4 ill H3PO4 



Bromauric acid is the most generally use- 

 ful of all amine precipitants. In phosphoric 

 acid it appears to precipitate all nitrogenous 



compounds in which the nitrogen manifests 

 any basic properties at all, external to ihe 

 molecule. The restriction of the last four 

 words applies only to a few "internal salts." 

 The only reagent that carries precipitation 

 even further in some cases is iodine-KI (or 

 HI) in H3PO4 . It precipitates even some 

 nitrogenous compounds that appear to be 



completely acidic (having an /NH group 



\ / 



flanked bv /C^O groups), as well as 





'.".^" ^-^j*^ A:.5-^'. 



Fig. 5a. Benzylephedrine with HAuCU (1 + 2) H3PO4 added to aqueous .solution of the salt. E.x- 

 traordinary "corkscrew" crystals. With crossed nicols they resemble metal-turnings. lOOX. 



Fig. 5b. Cyclopentamine with H^Ptle in (2J^2 + D H3PO4 , minimum Nal. 66X. (Propylhexedrine 

 gives similar crystals; test distinguishes those two from others.) 



70 



