High-path-difference optical compensator: its use in the observation of solid-solid phase transformations

A simple experimental method has been developed for permitting the visual observation of subtle structural transformations in transparent birefringent solids. The method makes use of an optical compensator with a large path difference in conjunction with standard equipment for polarized light microscopy. This method has been applied successfully in the observation of subtle phase transformations in p-diiodobenzene and in phenanthrene.