UNITED STATES DEPARTMENT OF AGRICULTURE 
h BULLETIN No. 679 
Contribution 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. 
Page. 
Optical properties in the identification of 
synthetic crystalline substances 
Methods for determination of optical 
constants: 
Apparatus 
Observations 
In ordinary light 
Page. 
Observations— Con tinued . 
In parallel polarized light 
In convergent polarized light 
Measuring the optical properties of an 
alkaloid 
Summary 
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 
dealing 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 
little 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., 
numerical, quantitative observations being made only exceptionally. 
U 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 
