(521) 
very meritorious, is not based on the analysis of free indican, but 
on the analysis of lead compounds obtained from extract of woad 
and has been accepted with a certain amount of reservation 1). Moreover, 
the important observations of BEYERINCK communicated at the September 
meeting on the chromogen of the woad have shaken the foundation 
of the formula. SCHUNCE’s coadjutor MaRcHLEwsKI *) had, however, 
already proposed another formula for indican in 1898, starting the 
hypothesis that it should be looked upon as indoxyl-glucoside; he 
even gave a structural formula illustrating the connection between 
the glucose residu and the indoxyl-group. MARCHLEWSKI has appar- 
ently not had material at his disposal to prove experimentally 
the correctness of his hypothetical indican formula Cy, Hj7NOg, 
although in the meantime indican has been proved to be a real 
indoxyl-glucoside *). 
The following circumstances enabled us to carry on the investigation. 
Prof.. BEIJERINCK had the kindness to present us with 17 kilos of 
his own grown Polygonum tinctorium for the extraction of the 
indican and also with an extract prepared by himself from the 
leaves of Indigofera leptostachya. From Mr. HAZEWINKEL we re- 
ceived tins containing somewhat purified solutions of indican pre- 
pared by himself from indigo-leaves at Klaten. We beg to offer 
them our best thanks for this co-operation. » 
The leaves were immersed by us in boiling water, boiled for a 
few minutes and further systematically exhausted; 2.5 liters of water 
were used for 1 kilo of the leaves. Without any sensible decompo- 
sition the decoctions could be evaporated in vacuo if care was taken 
to keep the reaction alkaline. The dry residue was extracted with 
methyl alcohol and to the solution was added ether as long as 
a precipitate was formed; these precipitates were rich in ash 
but very poor in nitrogen and were practically free frora indican. 
From the solution, the alcohol and ether were distilled off, the 
residue was completely dried in vacuo and then dissolved in water, 
The filtered and concentrated solution deposited on cooling well 
defined crystals of indican almost colorless and ash free. A large 
proportion of the impurities may be removed by heating the decoction 
of the leaves before concentration with baryta-water, filtering and 
removing the excess of barium by a current of carbon dioxide; the 
filtrate is then treated as described. If the treatment with baryta 
1) Compare BEILSTEIN Org. chem. 3 Aufl. Bd. IIL p. 595. 
?) MARCHLEWSKI and Rapcuirre Journal Soc, chem. Industry 1898 p. 430. 
3) Compare HAZEWINKEL and BeEYERINCK l.c. 
38 
Proceedings Royal Acad. Amsterdam, Vol. II. 
