The Optical Properties of Organic Compounds

Abstract

THE value of the polarizing microscope in identifying and characterizing minerals is well known, but its application to organic crystals is not yet by any means general. The customary description of a new compound includes a precise statement of its melting point, boiling point and other physical properties; but when it comes to crystalline form the description all too frequently lapses into the vagueness of white needles, orange prisms or colourless plates. A more careful description of superficial appearance is perhaps considered unnecessary because crystal habit is notoriously dependent upon environment during growth, and may vary from one preparation to another. If reasonably well developed crystal specimens are available, resort to the goniometer will provide data which are definitely characteristic of the compound. Very often, however, such well-developed specimens can only be obtained with considerable difficulty, and the material is more usually in the form of minute, even microscopic crystals or fragments of crystals. It is perhaps not generally realized that on such unpromising material the polarizing microscope can provide accurate measurements, not of one but usually of several distinct physical constants which, taken together, provide an exceedingly reliable means of characterizing the compound.

The Optical Properties of Organic Compounds

By Alexander N. Winchell. Pp. xiii + 342. (Madison, Wis.: University of Wisconsin Press, 1943.) 5 dollars.