Wakeman—Pigments of Flowering Plcmts. 883 
2. Methyl-2-anthraquinone. 
a. ) Trihydroxy methyl-2-anthraquinones. 
Morindon. 
b. ) Hexhydroxy methyl-2-anthraquinones. 
Pseudo purpurin. 
II. B. 1.) Pigments referable to methyl-l-anthraquinone. 
Five pigments of known constitution are referable to methyl- 
i-anthraquinone. These are rubiadin, a dihydroxy-2, 4-methyl- 
1-anthraquinone; chrysophanic acid, a dihydroxy-1', 4'-methyl- 
1-anthraquinone; emodin, a trihydroxy-3, 1', 4' -methyl-l-anth- 
raquinone; aloeemodin, a trihydroxy-3, 4', 5-methyl-l-anthra- 
quinone, and rhein, a dihydroxy-3, 4'-carboxy-l-anthraquinone. 
Dihydroxides of methyl-l-anthraquinone. 
Two pigments which are dihydroxides of methyl-l-anthra¬ 
quinone are known to exist in plants. These are rubiadin, 
dihydroxy-2, 4-methyl-l-anthraquinone, and chrysophanic acid, 
dihydroxy-1', 4'-methyl-l-anthraquinone. As would be ex¬ 
pected from their similar constitutions the two compounds re¬ 
semble each other quite closely in properties, though chryso¬ 
phanic acid has the better dyeing properties. The fact that 
chrysophanic acid possesses dyeing properties appears to be an 
exception to Liebermann ? s rule regarding the relation between 
dyeing properties and the number and position of hydroxy 
groups, since of the three structural formulae assigned to it by 
different investigators none have the two hydroxy groups in 
relatively 1, 2, positions, while the formula which appears to be 
preferred at present has its hydroxy group in 1', 4', relatively 
para position, a position which is supposed to give no dyeing 
properties to anthraquinone derivatives. 
Rubiadin, — -Dihydroxy-2, 4-mtehyl-l-anthraquinone. 
