Wakeman—Pigments of Flowering Plants. 
891 
Pseudo purpurin occurs along with purpurin in the root of 
Rubia tinctorium, 1 It comprises a large part of the purpurin 
of commerce. The constitution of the molecule does not ap¬ 
pear to have been yet definitely established. From the work 
of Rosenstiehl, 2 also that of Liebermann and Platt, 3 we learn 
the number and relative positions of the hydroxy groups. 
Perkin 4 has shown that the carboxyl group is in the second ben¬ 
zene nucleus, corresponding to one of the formulae given above. 
Pseudo purpurin crystallizes in small red leaflets. It melts 
at 218°-219°. It is almost insoluble in water and in alcohol, 
difficultly soluble in chloroform and hot benzene, easily soluble 
in solutions of alkaline carbonates with an orange color. Its dye¬ 
ing properties are almost identical with those of purpurin. 
The Aloins. 
Substances crystallizing in yellow needles and soluble in con- 
eentrated sulphuric acid with a red, in alkaline hydroxides and 
carbonates with an orange color, are found in various species of 
aloes. These are known as aloins. The formula of aloin has been 
variously given as C 16 H 16 0 7 , C 16 H 18 0 9 , C 17 H 18 0 7 . Accord¬ 
ing to Jowett and Potter who have performed some of the most 
recent work upon aloin, •C 16 H 18 0 7 is probably correct. 
The aloins, known as aloin, barbaloin, isobarbaloin, and na- 
taloin are closely related to the anthraquinone pigments. 
Jowett and Potter think, however, that instead of the anthra¬ 
quinone nucleus being present there is probably a reduced an¬ 
thraquinone nucleus. 
Upon treating aloin with sodium peroxide aloeemodin is 
produced. 
III. PIGMENTS REFERABLE TO PHENYL-HYDRINDINE AND HOMO- 
LOGUES. 
CH 
rH rw 
CH 
fi -methyl- y -phenyl hdyrindine 
1 Bull. Soc. Chim., 4, p. 12. 
a C. r., 79, p. 680; 84, p. 559, 1902. 
8 Ber., 10, p. 1618. 
* Jr. Chem. Soc, 65, p. 842. 
