SYMPATIIOMIMKI ICS \M> CENTRAL STIMULANTS 



Fig. 5c. Nylidrin, 1.3 HAuBr4 in 2H3P04-1 (2+ 3) H,804 (90), on standing, with humiditv. 

 lOOX. 



amphoteric compounds (even when mainly 

 acidic and only feebly basic) in which the 

 strong H3PO4 brings out the basic character; 

 this also occurs with bromauric acid in 

 H3PO4 . Iodine reagents are indispensable 

 but not more so than bromauric acid; the 

 iodine precipitates more often fail to crystal- 

 lize, and different reagent-formulas are 

 needed for them. 



In general, the precipitates are not neces- 

 sarily crystalline. With complex and defi- 

 nitely basic compounds, such as the alkaloids 

 and antihistamines, the precipitates with 

 HAuBr4 in II3PO4 , even when it is added to 

 an aqueous solution, are far too insoluble for 

 the best results. Such precipitates are usually 

 amorphous or too minutely crystalline to 

 have any value for microscopic crystal tests. 

 On the other hand, compounds that are rela- 

 tively simple but too water-soluble or too 

 feebly basic, or both, to yield precipitates 

 from an aqueous solution with reagents dis- 

 solved in water, will generally yield beautiful 

 crystals with bromauric acid in a medium of 

 phosphoric acid, although occasionally only 

 drops are formed. The crystals show great 

 differences from one compound to another, 

 not only in their forms, but also in colors, 

 birefringence, and dichroism. The reagent is 



added directly to the dry substance to be 

 tested. Crystals of the bromaurate com- 

 pound are easily distinguished from undis- 

 solved material, or any other crystals that 

 may form, by their color. 



The reagent also has a general use in de- 

 termining whether any compound capable of 

 this precipitation is present. A little powder 

 from a tablet, for example, may be scattered 

 thinly on a slide, a drop of the reagent and a 

 cover-glass applied, and bromaurate crystals 

 or precipitation looked for under the micro- 

 scope immediately and after standing. In 

 this direct addition there is some danger 

 that a compound with too great bromaurate 

 insolubility may not show up, because the 

 insoluble precipitate may completely cover 

 the surface of the material and prevent 

 further solution. Therefore, some less sensi- 

 tive reagents should also be tried, or the test 

 tried on an ac^ueous or dilute acid solution 

 of the substance, before concluding that no 

 compound of basic nitrogen is present. 



Precipitates may be due to other kinds of 

 basic substances. These include: 



(a) Inorganic: all the alkali metals, and 

 magnesium and zinc, in particular, in the 

 form of thcMr salts, as well as ammonium 

 and hvdroxvlnniine. 



71 



