ENDOTHIA PIGMENTS 
the acid properties of coloring matters of the anthraquinone, flavone, 
xanthone, and ketone groups. He says: "With the exception of morin 
and rhamnazin, no coloring matter of known constitution is markedly acidic 
unless it contains two hydroxyls in the ortho-position relatively to one 
another, and consequently has strong dyeing properties." Further evidence 
that the two hydroxyls are in the ortho-position in endothine red was 
obtained by fusing the compound with potash. By heating the pigment to 
2oo°-25o° C. for half an hour with ten times its weight of potassium hy- 
droxide, dissolved in a little water, a phenol portion was obtained, which 
gave a green coloration with ferric chloride. The fusion was carried out 
Several times, and at no time could the phenol be isolated in sufficient quan- 
tities for further identification. It is probable, however, that it is pyro- 
catechin or a member of this group since this class of phenols gives a green 
color with ferric chloride. A red acid portion of the potash fusion gave a 
greenish "raw sienna" color with ferric chloride and appeared to consist 
partly at least of the unchanged pigment. 
The foregoing considerations justify the conclusion that endothine 
red is probably related to the members of the pyrocatechin group. The 
exact constitution of a side chain, if such exists, and further confirmation 
of the meager evidence at hand will, it is hoped, be the subject of another 
investigation. 
Bureau of Plant Industry, 
Washington, D. C. 
