UNITED STATES DEPARTMENT OF AGRICULTURE 



I; BULLETIN No. 679 



Contribntion .rom the Bureau of Chemistry 

 CARL L. ALSBERG, Chie;' 



Washington, D. C. 



PROFESSIONAL PAPER 



May 20, 1918 



THE APPLICATION OF OPTICAL METHODS OF 

 IDENTIFICATION TO ALKALOIDS AND OTHER 

 ORGANIC COMPOUNDS. 



By Edgar T. Wherry, Crystallographer. 



CONTENTS. 



Optical properties in the identification of 



synthetic crystalline substances 1 



Methods for determination of optical 

 constants: 



Apparatus 2 



Ohserrations 3 



In ordinary light 3 



Page. 

 Observations — Continued. 



In parallel polarized light 5 



In convergent polarized light 6 



Measuring the optical properties of an 



alkaloid 8 



Summarv 9 



OPTICAL PROPERTIES IN THE IDENTIFICATION OF SYNTHETIC 

 CRYSTALLINE SUBSTANCES. 



Because crystals are best developed among minerals and were 

 first studied in that connection, the sciences of crystallography and 

 mineralogy have grown up in close association, and most of the 

 printed information on crystallography is to be found in the literature 

 deahng with mineralogy. Optical crystallography has been evolved 

 largely for the identification of minerals, especially as they occur in 

 rocks or as they are produced synthetically. To be sure, the crystal- 

 lographic constants and partial optical data have been measured on a 

 large number of artificial substances, both organic and inorganic, but 

 httle use has thus far been made of these observations for determina- 

 tive purposes. Although microchemical methods of identification 

 are used in a number of fields, the recorded data are largely qualita- 

 tive. For instance, a given substance, when treated with an appro- 

 priate reagent, yields "radiating needles," ''stout prisms," etc., 

 munerical, quantitative observations being made only exceptionally, 



"A careful study of much that has been written, and especially of 

 the illustrations that have been made, of microcrystals in plants and 

 drugs shows that erroneous conclusions may be easily drawn from the 

 general appearance of crystalline precipitates or aggregates of crys- 



49941°— 18— Bull. 679 



