IN continuation of earlier work on vitamin A we have investigated the ultraviolet absorption of certain products obtained after the vitamin has been decomposed. At the same time, we have tried to elucidate the mechanism of the antimony trichloride colour test.As is well known, the blue colour is transient, and for purposes of assay it is necessary to determine the intensity of colour during the first minute, as otherwise the rapid fading tends to vitiate the results. Little is known concerning the secondary reactions which occur, and even the primary process is not fully understood. For the full development of the blue colour, the reagent must be nearly saturated and, it would appear, the SbCl3/vitamin A ratio must be very high (order 20,000: 1). This fact suggests that the blue substance (or substances) is an addition compound; the hypothesis of more than one coloured addition complex has already been advanced to account for the two apparently independent absorption bands seen in the blue solutions [Gillam and Morton, 1931;Heilbron, Gillam and Morton, 1931]. It is possible that the primary process, resulting in the blue colour, leaves the vitamin A molecule intact, whilst the secondary reactions associated with the fading of the colour bring about decomposition. To test this view, the blue solutions have been poured into large volumes of water so that the antimony is precipitated as oxychloride. The organic matter is then recovered and its properties studied.The general method adopted is as follows. A known weight of liver oil or concentrate dissolved in chloroform is treated with a saturated solution of antimony trichloride in chloroform and the mixture shaken for one minute to allow the blue colour to develop fully. The solution is then poured into water in a separating funnel and shaken vigorously to complete the decomposition of the antimony trichloride. As it is impossible to separate the chloroform layer owing to the precipitated antimony oxychloride, the latter is brought into solution by careful addition of concentrated hydrochloric acid, when separation into two layers readily occurs. The chloroform extract is washed successively with sodium carbonate and water and dried over sodium sulphate. After removal of solvent, the residual oil (or concentrate) is very similar in appearance to the original material and in all cases gives a blue or

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THE present paper is the full account of work briefly reported elsewhere [Lovern et al. 1937; Edisbury et at. 1937]. The main experimental result is that fish viscera, and notably the pyloric caeca and intestines, are often very rich in vitamin A. Large deposits of vitamin in the absorptive parts of the alimentary tract make it necessary to study the possibility that vitamin A plays an essential part in food assimilation in some species. This idea is discussed in a preliminary fashion, whilst other aspects of the subject such as the physical properties of visceral oils, vitamin D content, phospholipid content, glyceride composition etc., await further study. Euler et at. [1928; 1929] showed that carotene displays vitamin A activity, in accordance with an earlier suggestion made by Steenbock. The accepted chemical structures and the known physical properties of P-carotene and vitamin A are consistent with a process 2H20 C4,H56-2C20H290H ,B-carotene 2 vitamin A first recognized in vivo by Moore [1929, 1, 2, 3]. His proofthat the administration of a diet rich in carotene results in the rat in a greatly increased accumulation of vitamin A in the liver has been confirmed and extended to fowls and rabbits [

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4 modified Emmerie and Engel test has been evolved to avoid norilinearity, high or variable blanks and the use of corrosive solvents. A solution of the saponified material in light petroleum is purified by chromatography, the tocopherol being adsorbed on mildly alkaline alumina, washed I\ itli diethyl etherlight petroleum solvent and subsequently eluted with chloroform. The eluate is concentrated by evaporation and treatccl with chlorolorm solutions of ferric chloride and 2 :2'-dipyridyl. -4fter the sohtion h , s stood for 5 minutes, a measured volume of water is added and the optical density of the aqueous extract is determined a t 520 m p ; altcrnati\dy the depth of colour, which is stable for some hours, may be assessed visually, e.g., by comparison with a standard cobalt sulphate solution. The only interference encountered has been from highly oxidised caroteiioids, for which correction is possible.Sensitivity is five times that of the original Emmerie and Enqel test and precision is about 5 per cent.