Cxxiv. Studies on Colour Tests for Sterols and for Vitamin A

IN the first paper of this series an account was given of some sterol tests in which blue colours were obtained very similar in appearance to those given by arsenic trichloride or antimony trichloride with cod-liver oil, and attributed to vitamin A. On account of this close resemblance, it appeared desirable next to undertake a spectroscopic study of the "vitamin" colours with the object of discovering specific absorption bands by means of which the chromogen might be identified. Examination of the literature brought to light two cases in which workers had previously examined this question. Rosenheim and Drummond [1925] mentioned that the absorption band of the blue colour given by the action of arsenic trichloride on cod-liver oil lies between 570 and 590p,u. Euler, Myrback, Fink and Hellstrom [1927] have recently employed a spectrographand Siegbahn registering microphotometer to record the absorption bands in the colours given on two samples of Norwegian cod-liver oil by both arsenic and antimony trichlorides. Their results with arsenic trichloride indicate the existence of two bands, one between 475 and 480,u, and a second at about 535,pu. Both of these are well outside the range 570 to 590,u, mentioned by Rosenheim and Drummond. In the case of antimony trichloride, again two bands were found, one between 475 and 482,u,u, and a second between 535 and 550,u,u. Since these figures, which were the result of only two experiments with each reagent, showed a somewhat wide variation in themselves, and also did not agree with the earlier findings of Rosenheim and Drummond, it was considered desirable to carry out a more detailed study.