822 BOTANY AND PHARMACOGNOSY. 



servations had to be interpreted and applied to crystals which 

 were formed upon microscopic slides. The author was fortunate 

 in having the co-operation of Charles Travis, Ph.D., of the 

 University of Pennsylvania, to whom is due the credit for the 

 careful studies of the crystals described in this part of this text- 

 book. 



A rather large number of substances were examined and 

 only a few of the more important are included at this time. 

 While drawings might have been made to illustrate the form 

 of crystals and optical orientations it was deemed advisable 

 to use some of the photo-micrographs made by the author. 

 The four-color plate is introduced to show the chromatic effects 

 observed by using crossed nicols. The plate illustrates salicin 

 and cocaine hydrochloride and is a nearly exact reproduction of 

 the effects obtained with the micro-polariscope, the electros 

 having been made from Lumiere autochrome plates, using direct 

 sunlight. 



The method of obtaining the crystals was rather simple. The 

 solvents used were distilled water, alcohol, ether, chloroform 

 and a mixture of chloroform and alcohol. To a weighed amount 

 of the substance was added a sufficient quantity of solvent to 

 give a saturated solution. A drop of this w^as added to a slide 

 which was covered either with a bell- jar or the cover of a Petri 

 dish. If the crystals formed too rapidly, giving rise to crystal 

 aggregates, more dilute solutions were made from the original 

 solution until single crystals were obtained therefrom. In some 

 instances as with physostigmine salicylate, where the edges of 

 the crystal are likely to be re-dissolved, the slides were finally 

 dried in a desiccator over sulphuric acid. With caffeine gold 

 chloride, the best crystals were obtained when the solutions were 

 relatively weak. Again, it was found that after crystals were 

 mounted in balsam, as cocaine hydrochloride, caffeine gold chlo- 

 ride, etc., that the isolated crystals grew considerably in size at 

 the expense of amorphous material. A rather unique instance 

 of growth of large crystals was with menthol when the slide con- 

 taining the silky aggregates was covered with another slide. 

 Finally it should be stated that some patience and experience are 

 necessary to obtain satisfactorv crvstals. 



