CHAPTER X 

 MICROANALYTICAL STUDY OF CRYSTALS 



In addition to the widely distributed (in the plant kingdom) and 

 in many instances highly diagnostic crystalline forms of calcium oxalate, 

 the student of pharmacognosy will frequently meet with other crys- 

 talline formations, such as those of fats, of acids, of alkaloids, of alka- 

 loidal salts, etc. He should familiarize himself with the microscopical 

 appearance of the principal form types as such knowledge is frequently 

 of great value in arriving at a better knowledge of the identity and 

 quality of vegetable drugs and of many of the preparations made 

 therefrom. Such a study will also serve as an introduction to the 

 critical microscopical examination of face lotions, so-called vanishing 

 creams, salves, ointments, fats, oils, etc. 



The entire field of crystallography is still in great confusion, for 

 which reason it would be unwise to enter into a discussion of polari- 

 scopic behavior, extinction angles, axial structure, optical characters, 

 form types, etc. Those especially interested may consult the classic 

 German works on the subject, some of which date back fifty 

 years and more. The Zeitschrift fur Krystallographie is devoted en- 

 tirely to this subject; besides there are a number of recent manographs 

 on physical crystallography, microscopic crystallography, chemical 

 crystallography, etc. 



For a practical study of crystals the following solvents are desirable. 



1. Distilled water. 



2. Alcohol. 



3. Ether. 



4. Chloroform. 



5. Alcohol and chloroform mixed. 



6. Acidulated water (HC1 and H 2 S0 4 ). 



Crystals of the more common metallic salts (chlorides, sulphates) 

 may be obtained from solutes in the distilled water. Very dilute 

 solutions should be used in order that single crystals may appear 

 upon the slide. The rate of evaporation, temperature, impurities 

 present, etc., greatly influence the size and form of the crystals. 

 Drawings should be made of the crystals, noting variations in size 



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