QUANTITATIVE ESTIMATION OF CAROTINOIDS 255 



T.UiLE 19. CAUOTIN AND XANTHOPHTLL CONTENT 01 I.i.ui.s (Mi-Tilou UK 



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writer is inclined to believe that the ratio of 1.5 to 2 molecules of 

 xanthophyll to 1 of carotin, as found by Willstatter and Stoll, repre- 

 sents more nearly the true proportion between the two classes of 

 carotinoids as they exist in green leaves. 



Elizabeth Goerrig (1917) has applied the general principles of the 

 Willstatter and Stoll method to the determination of the carotin and 

 xanthophyll content of yellow autumn leaves. This work has already 

 been discussed in Chapter II in connection with the pigments of 

 autumn leaves, but it might be well to mention here Miss Goerrig's 

 experience in applying the method. She varied the procedure in sev- 

 eral particulars, one of the most important of which, as far as its 

 possible effect on her results is concerned, was the preliminary drying 

 of the leaves at 40 C., instead of using the fresh leaves as recom- 

 mended in the original method. Miss Goerrig admits that- the dried 

 leaves were difficult to grind with the extraction solvent and, in fact, 

 states that the yellow leaves usually retained a part of the color which 

 could not be extracted by the method recommended. Moreover, 

 the calculation of the carotin content of some of the leaves using Miss 

 Goerrig's data, which arc expressed as colorimeter readings only, gives 

 results much lower than Willstatter and Stoll reported for leaves from 

 the same species of plant. Another important particular in which 

 Miss Goerrig modified the Willstatter procedure was the omission of 

 the preliminary extraction with 30 per cent acetone and the use of 

 85 to 90 per cent acetone for the extraction of the pimncnts instead of 

 the pure acetone recommended. Finally, Miss Goerrig used a 0.4 per 

 cent K,Cr 2 O. solution as a standard in place of a 0.2 per cent solu- 

 tion. By setting the standard at 50 mm. a greater range of color in- 



