VITAMIN A 239 



Fearon (1925) proposed the substitution of phosphorus pentoxide 

 for sulfuric acid, and discussed at length the results yielded by these 

 tests. He also developed a color test using pyrogallol and trichloroacetic 

 acid, which he believed to be due to the same substance as the former 

 tests. 



Willimott and Moore (1926) found that Fearon's pyrogallol test is 

 not specific for vitamin A, however. A sample of oil which had been 

 exposed to ultra-violet light gave a positive Fearon test after 3}^ hours, 

 but failed to respond to the arsenic chloride test after only Ij^ hours 

 exposure. A sample of oil shaken with concentrated sulfuric acid and 

 then washed with water had no vitamin A potency when fed to rats, but 

 gave a positive test with pyrogallol. 



Further Rosenheim and Webster (1926b) stated "Since we found 

 . . . that Fearon's color reaction is not given by the unsaponifiable 

 fraction of cod-liver oil, it is evident that this reaction has no relation 

 to vitamin A." 



Carr and Price (1926) investigated a number of condensing agents, 

 and found antimony trichloride to be the most suitable and convenient 

 of all the reagents tested for use in color tests of vitamin A. The con- 

 ditions which they adopted for its use are essentially as follows : Anti- 

 mony trichloride washed with chloroform and dried is dissolved in 

 chloroform to make a 30 per cent solution (weight in volume). After 

 standing, the clear solution is decanted and used from a burette. The oil 

 to be tested is dissolved in chloroform (20 per cent solution) and to 

 0.2 cubic centimeter delivered from a 1 cubic centimeter burette, 2 cubic 

 centimeters of the antimony trichloride solution is added. The liquid 

 is at once transferred to a cell and the blue color intensity measured 

 against standard glasses in a Lovibond tintometer. 



Willimott and Moore (1926) also recommended antimony chloride 

 as more suitable than arsenic chloride, as it gives colors which persist 

 longer. Either test, however, appeared to be more sensitive than the 

 sulfuric acid or phosphorus pentoxide test. 



The literature on color tests for vitamin A was reviewed briefly by 

 Willimott and Wokes (1927b) and a summary was given of the results 

 obtained in attempts to apply several of the tests to cod-liver oil, food- 

 stuffs, and various natural products from which interfering pigments 

 had been removed by shaking the material in petroleum ether solution 

 with an adsorbent charcoal, preferably norite. Tables were given of the 

 results obtained with the concentrated sulfuric acid, phosphorus pent- 

 oxide, arsenic trichloride, and antimony trichloride color tests, together 

 with an estimation of the activity of the materials tested by rat feeding 



