98 



thesin, beta-eucain, holocain, gujasanol, and acoin. The dilution of the alkaloid 

 in the solvent in many cases has a most marked effect upon the form assumed by the 

 precipitate. There is always a limit beyond which the dilution of the product is 

 too great for crystallization to take place, while on the other hand the concentration 

 may be so great as to cause too sudden precipitation and an unsatisfactory product 

 results. In this work dilutions of 1 : 100 or 1 : 200 were most frequently tested. Other 

 dilutions would possibly have given crystalline products where only noncrystalline 

 products have, thus far been obtained or where no reaction at all has been noted. 



The reagents used embraced a list of more than ninety compounds or mixtures 

 and included the standard reagents and as far as known, the special alkaloidal reagents 

 with the exception of two or three which have recently been brought to the authors' 

 attention. Thus far crystalline precipitates have been obtained in about 400 combina- 

 tions. Noncrystalline deposits resulted in nearly 600 other combinations, but their 

 usefulness in identification is very limited and they can usually only be employed 

 as corroborative tests. 



Unfortunately some of the well known alkaloidal reagents, though giving reactions 

 with most of the alkaloids, produce only noncrystalline precipitates. As ordinary 

 analytical tests they may be satisfactory, but as microchemical reagents they leave 

 much to be desired. To the analytical chemist they serve a good purpose as indicating 

 alkaloidal presence, but rarely its identity. This is shown in the following examples: 

 Mayer's reagent, 11 crystalline, 23 noncrystalline; Kraut's reagent 10 and 33 and 

 Marine's reagent 11 and 25, respectively. 



Picralonic acid gave 21 crystalline precipitates out of 37 positive reactions, but 

 the forms unfortunately are in most cases too much alike to be of much sevice for 

 identification. The alkaloids studied showed a great diversity in the character of 

 the precipitate formed, as is seen from the following examples, which serve to illus- 

 trate the extremes, the first four giving a high number of crystalline forms, the last 

 five giving a high number of noncrystalline. 



Character of precipitate obtained with different alkaloids. 



With piperin, sanguinarin, emetin, and apocodein noncrystalline precipitates only 

 have been obtained thus far, though it may be that by some change of manipulation 

 crystals may yet be produced. 



The melting point of the products is likely to be of service at times in establishing 

 the identity of certain compounds though some of the precipitates apparently are 

 too unstable for this test. For this purpose, however, an apparatus which had been 

 devised in the Bureau of Chemistry for use on the stage of the microscope has been 

 tested with promising results. It allows of the microscopic examination and deter- 

 mination of the melting point of an individual crystal in a mixture of various kinds 

 either with plain or polarized light. In some crystals, especially some of the compact 

 spherical forms, this last point is an important means of telling where melting begins, 

 since as soon as a crystal melts it loses its polariscopic activity, and as all systems, 

 except those belonging to the regular system, are active this feature can be used to 

 advantage in determining the point where melting begins and where it ends even on 

 small crystals. 



