The fluorescence of some vitamin A-containing fats.

WHEN a beam of light from a quartz mercury vapour lamp, completely enclosed so that the only light emitted has to pass through a filter cutting out nearly the whole of the visible portion of the spectrum, is allowed to fall on to any object in a darkened room, a more or less characteristic fluorescence is usually observed. Metals, such as gold, silver, iron, etc., are quite nonfluorescent and take on the appearance of black velvet when observed in this light, but many other substances emit quite a bright coloured light. Several references are to be found in the literature suggesting the application of this phenomenon in various branches of analysis (e.g. Gerngross and Schulz [1927]; Popp [1927]; Volmar [1927]), and perhaps the most striking observation is that butter can be distinguished from margarine by the quite dissimilar fluorescence. Butter shows a fairly bright yellow colour, but margarine in this light is definitely blue.