Colour Reactions Attributed to Vitamin A

Abstract

HAVING regard to the wide variation in the vitamin A activity of different cod-liver oils, it is a matter of practical importance to find the most ready means of assessing their relative activity.The long period of time occupied in carrying out the biological test renders this method not only tedious and expensive, but impractical from the point of view of industrial establishments requiring to accept or reject oils under conditions allowing at most one or two weeks for a decision.There is already good evidence that the well-known colour tests described by various workers, notably by Rosenheim and Drummond, may be expected ultimately to form a basis for a satisfactory chemical method of determining the vitamin value with great rapidity and approximate accuracy.All oils received in our laboratories for some time past have been submitted to these tests, in the first instance to the sulphuric acid test, and later to the trichloro- acetic acid and arsenic trichloride tests of Rosenheim and Drummond.Biological tests have been applied to some of these oils.We were naturally led, therefore, to make experiments with a view to improving the technique of the colour tests in order to find conditions whereby quantitative and strictly comparable readings may be obtained.This work has resulted in our utilising for the purpose yet another reagent of a similar character, namely, a solution of antimony trichloride in chloroform.By its use we have been enabled to determine standard conditions whereby direct readings of the intensity of the colour may be taken with the help of a tinto- meter.By following the conditions laid down observations made by different