CHEMICAL MICKOCRYSTAL IDENTIFICATIONS 



individual character of the tests is much 

 more an advantage than a defect. Here, 

 highly characteristic and specific tests, the 

 results of which can be photographed for 

 possible introduction in court or in other 

 proceedings, are welcomed. Here, it is a great 

 advantage that the tests are simple and di- 

 rect, and distinctions made on the basis of 

 obvious, visible characteristics. The identi- 

 fications clearly distinguish between closely 

 related compounds, even between an isomer 

 and the racemate, and by certain tests, be- 

 tween the d- and Z-isomers; and this is just 

 what is needed in the drug field and in 

 forensic chemistry and related work. 



In these applications the microcrystal tests 

 are already used, and so too are color tests, 

 of a kind with which the crystal tests form 

 a natural partnership. 



The classification of the microcrystal tests, 

 to enhance and extend their usefulness, re- 

 mains a problem. Compounds are onty too 

 likely to be met with occasionally, to which 

 the tests are applicable but which still can- 

 not be identified. This of course is due not 

 merely to lack of classification, but is, at 

 present, primarily because the tests for so 

 many new drugs and other compounds have 

 not been studied at all. However, this is a 

 related aspect of the problem, for if a satis- 

 factory system of classification is once 

 worked out, the necessary experiments to 

 find where all the compounds likely to be 

 met with fit into the scheme are more likely 

 to be made. 



WTiether a classification of crystal results 

 should be primarily chemical, or morphologi- 

 cal with the different reagents, or based simply 

 on the fact of crystallization of each sub- 

 stance with certain reagents out of a stand- 

 ard list, there can be no reasonable doubt 

 but that the science of microcrystal tests 

 should be integrated with analytical chem- 

 istry, not pushed aside as a "specialty" nor 

 even regarded as being more microscopy 

 than chemistry. 



The idea of using the microscope to make 



tests better for identification by simply look- 

 ing at the different crystals formed in the 

 usual precipitation reactions and other crys- 

 tal-forming reactions of chemistry seems so 

 sensible and also so obvious that it is hard 

 to explain how it can be overlooked, as it 

 usually seems to be. The idea develops nor- 

 mally in three stages: 



(1) Microscopic observation of chemical 

 tests: The microscope is used to distinguish 

 the crystals occurring in chemical precipita- 

 tion tests and other reactions, and thus to 

 particularize them further; and the tests 

 which are found especially characteristic are 

 noted. 



(2) Microscopic study of microcrystal tests: 

 The tests thus found of especial value be- 

 come in themselves the basis for identifica- 

 tion, and the best reagents thus found are 

 tried systematically on other, related com- 

 pounds. In this stage, appreciation of the 

 chemical nature of the tests sometimes al- 

 most disappears. 



(3) Chemical extension of microcrystal 

 tests: Chemical reagents and reactions are 

 reconsidered and studied with the objective 

 of improving microcrystal tests and extend- 

 ing them to new groups of compounds. As 

 the tests come to cover a wider area in or- 

 ganic chemistry than simply "alkaloids", 

 their chemical meaning in various cases be- 

 comes important. 



The chemist needs the microscope, not 

 only for primarily observational use, as in 

 looking at the material he is dealing with, 

 and as a convenient aid in all kinds of chemi- 

 cal procedures and research, for example, 

 whenever he has a deposit or residue and 

 merely wants to know whether it is crystal- 

 line or not. . . . He needs the polarizing mi- 

 croscope, not only as a means of identifying 

 crystals of chemical substances by refractive 

 indices and other properties shown by opti- 

 cal crystallography. . . . Most of all, in his 

 own capacity of chemist, he needs it, as this 

 article has tried to show, in analytical iden- 

 tification chemistry, as the prime means of 



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