PROPERTIES AND METHODS OF IDENTIFICATION 219 



of water have been added. This evaporation must be carried out 

 in vacuum aided by a little heat. 



Solutions of carotin are unaffected by boiling with alkalis, and 

 may be recovered unchanged from such solutions. When dissolved 

 in petroleum ether and carbon disulfide, carotin is not adsorbed by 

 finely divided substances like calcium carbonate, inulin or powdered 

 sucrose. However, according to Tswctt (1906b), carotin is adsorbed 

 from petroleum ether solution by finely divided HgCl 2 , CaCl 2 and 

 PbS. Miss Stephenson (1920) has reported that butter fat dissolved 

 in three volumes of petroleum ether can be completely decolorized of 

 its carotin by shaking for several hours with a special birchwood 

 charcoal, using 2.5 grams per 100 grams of fat. The writer has 

 experimented with a number of decolorizing carbons without being 

 able to duplicate this result. In strictly adsorption experiments in 

 which there was no indication that decolorization was due in part 

 to oxidation of the carotin, it was found that at least five times this 

 amount of the most effective carbon so far obtainable was required to 

 completely adsorb the carotin. The fact that carotin is not adsorbed 

 from its petroleum ether solution by calcium carbonate distinguishes 

 the pigment sharply from some of the other carotinoids, particularly 

 the xanthophylls. As a corollary to this property, when a petroleum 

 ether or carbon disulfide solution of carotin is filtered through a column 

 of tightly packed, perfectly dry calcium carbonate, which has first been 

 moistened with the solvent (Tswett's chromatographic analysis) the 

 carotin passes through unadsorbed. When carbon disulfide is used the 

 zone of carotin usually has a characteristic rose color. 



Alcoholic solutions of carotin are not characterized by giving color 

 reactions on addition of concentrated HC1, HN0 3 or H 2 S0 4 as are 

 certain of the xanthophylls, although in most cases the golden yellow 

 solutions change slowly to a deep green before fading. The com- 

 plete fading of this green solution may require several days. The 

 addition of NH 4 OH to the green solution will restore the yellow 

 color, although the color is somewhat lighter than the original, and 

 the green color can be renewed by adding acid. Solutions of carotin 

 in oil or melted fat give a beautiful green color reaction on dis- 

 solving a very small crystal of Fe 2 Cl 6 in the warm oil or fat. A 

 few tenths of a milligram of the iron salt is sufficient to add to 5 cc. 

 of well colored oil. The reaction is very delicate, and is given by 

 xanthophylls as well as carotin. Palmer and Thrun (1916) found 

 that this reaction is caused by the oxidation of the carotinoid, the 



