Wakeman—Pigments of Flowering Plants. 
877 
II. A. 1.) Monohydroxy anthraquinone pigments. 
Of this group of dihydroanthracene derivatives only one 
representative, the monohydroxy -2- anthraquinone, is known. 
O 
iCH 
COH 
Monohydroxy -2- anthraquinone was first isolated from Olden - 
landia umbellata by Perkin and Hummel 1 in 1893. It crystal¬ 
lizes in glistening yellow needles which melt at 302°. Solu¬ 
tions of the alkali hydrates dissolve it, forming a red liquid 
from which it separates, when very concentrated, in thin red 
plates of the corresponding salts. Sulphuric acid dissolves it 
with a red color. 
Monohydroxy -2- anthraquinone does not combine with mor¬ 
dants to form a dye. 
II. A. 2.) Bihydroxy anthraquinone pigments. 
Of this group of dihydroanthracene derivatives three repre¬ 
sentatives have been isolated from plants. These are dihydroxy 
-1, 2- anthraquinone, alizarin; dihydroxy -2, 3- anthraquinone, 
hystazarin; and dihydroxy -1, 3- anthraquinone, xanthopur- 
purin. 
Alizarin—Dihydroxy -1, 2- anthraquinone. 
HC 
1 Jr. Chem. Soc., 63, p. 1178; 67. 820. 
