AOAC Official Method 939.08 Optical-Crystallographic Properties of Beta-Ionone-m-Nitrobenzhydrazide
Procedure
This substance in mass is yellowish, but when examined in ordinary light under microscope it is essentially colorless and crystallizes in thin,rod-like plates, many having lath-like or frayed ends, some having 6-side outline. In parallel polarized light (crossed nicols), extinction is parallel and sign of elongation negative. Refractive indices are the minimumvalue,na = 1.548, invariably shown on elongated fragments when their long dimension is parallel to vibration plane of lower nicol (lengthwise), and maximum value, ng = 1.648, usually shown on elongated fragments when their long dimension is at right angles to vibration plane of lower nicol (crosswise).
Reference: JAOAC 22, 390(1939).
