The first x-ray crystallographic study of calciferol (vitamin D2) was undertaken in 1932 by J.D. Bernal. In 1948 Hodgkin and J.D. Dunitz resolved the conflict between the early crystallographic and chemical evidence on the structure of calciferol by the complete x-ray analysis of a calciferol derivative (Bibliog. 44), but such was the complicated atomic arrangement in crystals of calciferol itself that it was not until 1976 that x-ray methods had advanced far enough for the arrangement to be established.