232 DR. E. SCHUNCK ON ANTHRAFLAVIC ACID. 



alkaline solution, changing the violet, due to alizarine 

 itself, into purple, or, when present in larger quantity, 

 into red. From the same cause an alkaline solution of 

 crude alizarine does not show the absorption-bands in the 

 spectrum so distinctly as one of pure alizarine. Alkaline 

 as well as alcoholic solutions of anthraflavic acid absorb 

 the blue end of the spectrum very powerfully (though no 

 bands are visible) even with very dilute solutions. A solu- 

 tion of the acid in concentrated sulphuric acid, however, 

 if not too dark, shows a broad but well-defined absorption- 

 band on the border of the blue and green of the spectrum, 

 accompanied by a total darkening of the violet end. 



If pure anthraflavic acid be dissolved in an excess of 

 caustic potash-lye, and the solution be boiled down to 

 dryness, a yellow residue is left, which, after being care- 

 fully heated almost to fusion, dissolves in water with a red 

 colour. This solution contains alizarine, as it shows the 

 absorption-bands in the spectrum peculiar to the latter — 

 though not very clearly, on account of undecomposed 

 anthraflavic acid still present. Pure alizarine may, how- 

 ever, be obtained from it by adding an excess of acid, 

 filtering off the flocculent precipitate, dissolving the latter 

 in alcohol and adding to the solution acetate of lead, when 

 a purple precipitate falls, which contains the whole of the 

 alizarine, the excess of anthraflavic acid remaining in 

 solution. The lead precipitate, suitably treated, yields 

 pure alizarine. It appears therefore that by the action of 

 caustic potash anthraflavic acid is converted into alizarine. 

 It should at the same time be stated that the conversion 

 is never complete, probably because the action, if carried 

 far enough to convert the whole of the acid, leads to the 

 decomposition of the alizarine already formed. 



Though anthraflavic acid gives, with bases, compounds 

 of an intensely yellow colour, it seems to possess no dyeing 

 properties. The freshly precipitated acid, suspended in 



