The crystal-structure of the bismuth oxyhalides

A. De Schulten published a crystallographic and optical investigation of the bismuth oxyhalides in 1900. He succeeded in preparing minute square plates capped with pyramidal planes, but evidently the difficulties of manipulation prevented the measurement of interfacial angles. He did, however, record a negative uniaxial figure observed in a direction perpendicular to the plane of the square plates of all three salts BiOCl, BiOBr, and BiOI. The present work was undertaken to extend A. de Schulten's observations, to measure the axial ratios, and to determine the crystal-structure.