AbstractsChemistry

min A is commonly determined by spectrophotometry or by measurement of the colour produced by its reaction with antimony trichloride. The complex nature of many vitamin A preparations makes it necessary to evaluate these physical and chemical methods against biological assays. Many such comparisons have been reported in the literature but the work carried out before 1948 is subject to the errors arising from the lack of a pure, stable, standard preparation. It is somewhat astonishing, therefore, to find that a comparatively limited use has been made of the biological assay since crystalline vitamin A became available. [...]