CHEMICAL MICROCRYSTAL IDENTIFICATIONS 



However, the question is whether the crys- 

 tals in a particular case are sufficiently differ- 

 ent from most others, or from all others, to 

 be distinguished from them by informed 

 direct observation. The writer is satisfied to 

 call most of these crystal tests, even most 

 of the very good ones, characteristic rather 

 than specific; not only when we know of 

 some definite resemblance but also whenever 

 the crystals are some general type that might 

 occur with some other compound, even if 

 we do not yet know what it would be. 



However, as an example of a specific test 

 the intensely pleochroic crystals of hera- 

 pathite, as a test for quinine, may be cited. 

 These crystals of quinine iodosulfate (Fig. 

 2), produced by a suitable reagent, are rec- 

 ognizable at once and the test is so sensitive 

 to cjuinine, and so insensitive to interference, 

 that the writer has used it as a direct test for 

 quinine in the diluted, adulterated, impure 

 heroin mixtures of the illicit drug traffic. 

 Of course, one almost never depends wholly 

 upon any single test by itself, even if it is 

 specific and the intense fluorescence of qui- 

 nine sulfate solution in ultraviolet light, 

 which is characteristic but not specific, is 

 also easily observed. 



Other cinchona alkaloids give highly char- 



iA 



*^% 





./«■■ 



^|i' 





^'•i*'^ . ^-^v^ 



■y^-^^ 



y 



Fig. 2. Crystals of quinine iodosulfate (hera- 

 pathite) (with polarized light). lodine-KI reagent 

 C-3 or a similar reagent. 



Fig. 3. Crystals produced by quinidine with 

 lodine-KI reagent C-3 or a similar reagent. 



wn 



Fig. 4. Crystals produced b.y Cinchonidine 

 with lodine-KI reagent C-3 or a similar reagent. 



acteristic, wholly different, iodosulfate crys- 

 tals, with the same reagent used for quinine 

 (Figs 3, 4, 5). 



A strange objection is often made to crys- 

 tal tests as, supposedly, a reason for not us- 

 ing them: that one substance with one re- 

 agent may give two or more different kinds 

 of crystals. This undoubtedly happens, but, 

 in the first place, it also happens with all 

 other tests that depend on crystal form and 

 properties, including melting points. As a 

 difficulty it is very unlikely to be too serious 



27 



