CHEMICAL MICROSCOPY 



Fig. 5. A well-known crystal test: cocaine with 

 H2PtCl6 (aqueous solutions). 



Y^^--M^ 







"W 



Fig. 6. A less-known alkaloidal crystal test: 

 (2) quinine with mercuric chloride and HCl (aque- 

 ous solutions). 



nitrogen, usually of a fairly high degree of 

 complexity. There are now numerous drugs 

 that are not considered alkaloids, but which 

 have the same characteristics: they are nitro- 

 gen-bases, soluble in dilute acids, precipi- 

 tated by exactly the same general reagents, 

 and give characteristic crystals with certain 

 of them (different ones, depending on the 

 compound), just as the alkaloids do. Among 

 these are the synthetic narcotics, local anes- 

 thetics, antihistamines, antimalarials, atro- 



pine-like drugs and some kinds of tranqui- 

 lizers. In some cases, whole classes of these 

 drugs are recent introductions, and for all of 

 them, the number in use has expanded 

 greatly in recent years. 



E. G. C. Clarke has given microcrystal and 

 color tests for 101 alkaloids (including those 

 synthetically modified), and for 15G of these 

 other drugs (to the date of writing), with 

 the same reagents. 



Other classes of drugs which are amine 

 bases are the sympathomimetics and central 

 stimulants. Some of these also give good tests 

 with the traditional aqueous reagents. 

 Others, relatively simple in structure and 

 often having hydroxyl groups, may be too 

 water-soluble in their compounds for good 

 tests in this way, and precipitation in phos- 

 phoric-acid solution is used. 



Many different acidic and anionic re- 

 agents are available for basic compounds 

 and it would seem that it should be equally 

 possible to use basic reagents or cations to 

 provide microcrystal tests for acidic com- 

 pounds, at least those of some complexity. 

 As a matter of fact, tests have been pub- 

 lished for various acids using salts of silver, 

 lead, copper, nickel, mercury, zinc, and pal- 

 ladium, usually in a solution made slightly 

 basic with ammonia, pyridine, triethanol- 

 amine, or the like. Such tests are useful but 

 as yet most of them hardly seem in the same 

 class with the better alkaloidal tests, either 

 for proving identity or in sensitivity, and 

 much study to develop good tests is needed. 



Aqueous Precipitation of the Free 

 Substance. Many alkaloids are precipi- 

 tated from acid solution by making the 

 solution basic, or even, in the case of weak 

 bases, by merely reducing the acid strength, 

 for example with potassium acetate. Charac- 

 teristic crystals are often produced and the 

 tests also give chemical information merely 

 by the fact of precipitation. The strength or 

 weakness of the base is shown to some degree 

 by the strength of the basic reagent required 

 for sensitive precipitation. K2Cr04 may pre- 



16 



