Herapathite–the first man-made polarizer

Abstract

Recent research reported earlier this year in Science has now determined the crystal structure of the salt of quinine first described by William Bird Herapath in 1852 in Philosophical Magazine and subsequently given the name ‘herapathite’ in his honour by the scientific community. This relatively obscure and little-known biaxial material was the forerunner of Polaroid: it exhibits the property of pleochroism, to the extent that light is almost completely absorbed along one particular principal vibration direction of the crystal structure. The story of herapathite is a fascinating one, unfolding gradually over more than 150 years and involving low temperature chemical synthesis and structure–property relationships in materials.

Keywords:

• absorption
• polarization
• crystallography
• optical microscopy
• crystal structure
• optical properties