CHEMICAL MICROCRYSTAL IDENTIFICATIONS 



brown threads in rosettes, tiny rectangular 

 orange-brown blades, and comparatively 

 large brown to red square-cut and jagged 

 birefringent plates. All four -kinds can be 

 obtained with only a few micrograms of 

 morphine (in a small spot) ; the black needles 

 are sensitive, with no special effort to reduce 

 the scale, to 0.1 microgram. The test is ex- 

 traordinarily resistant to interference, that 

 is, the morphine need not have a high degree 

 of purity to yield good crystals; in fact, the 

 black needles and red plates have been ob- 

 tained on a little dried poppy-juice (Papaver 

 somniferum) without first separating the 

 morphine from the other opium alkaloids or 

 even purifying the alkaloids as such (Fig. 

 6b). 



That specific tests are available for some 

 substances is only one factor in deciding 

 what tests to use in given circumstances. 

 Even a very general reaction may be useful 

 to prove the absence of a compound. For 

 general identification work, reagents will be 

 preferred which give many different charac- 

 teristic results, rather than "tailor-made" 

 reagents for a few specific results, particu- 

 larly in using them before one has much 

 idea what is present. Other important factors 

 are sensitivity, and ease of obtaining crystals 

 even when the substance is not quite pure. 

 Some specific tests rank high in these ways 

 also, but they do not necessarily go to- 

 gether. Regardless of other factors, there are 

 always cases where what we want, when we 

 can have it, is a test that, when successful, 

 will prove the identity of the substance then 

 and there, beyond doubt. This is possible 

 with some microcrystal tests. 



The very diverse nature of microcrystals is 

 at the same time the strength and weakness 

 of the method. The results are highly char- 

 acteristic or specific, but they are hard to 

 classify. Largely, this is due to the fact that 

 the tests are not measurements; the results 

 are not even directly numerical at all, and 

 so they lack the automatic classification that 

 numbers give. It is not that the tests are 





Fig. 6b. Crystals given by Morphine in dried 

 juice from Popaver somniferum — ^no purification of 

 the morphine, not even any separation of the al- 

 kaloids — with lodine-KI reagent M-2. 



good for only a few particular results: plenty 

 of good results are obtainable. The difficulty 

 is to have a way to look them up if they are 

 not already familiar. 



Possible solutions are being sought, now 

 that the problem is becoming acute. Even if 

 anyone wanted still to limit the scope of the 

 tests to some 50 familiar alkaloids, it is not 

 possible even in the drug field, for there is 

 now a host of new drugs that react in the 

 same way (by precipitation and crystal- 

 forming reactions) with the same traditional 

 reagents. Several different solutions of the 

 classification problem are possible in prin- 

 ciple, at least such that punched-card sorting 

 would quickly lead one from results on an 

 unknown back to the proper "known" if it 

 had been previously studied and classified. 

 However, at present, and probably for some 

 time, the analyst has to rely largely on 

 chemical classification, involving method of 

 isolation, color reactions, precipitation re- 

 actions regarded chemically, and any other 

 clues. Chemical evidence may reduce the 

 number of compounds that have to be con- 

 sidered to something manageable, and then 

 microcrystal tests will show exactly what 

 the substance is, if "knowns" for compari- 



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