DR. C. B. PLOWRIGHT ON WOAD AS A BLUE DYE. 
139 
Chemistry of VVoad, drew attention to the fact that indigo did not 
exist as ready formed indigo-white in this plant. He showed that 
a substance, indican, C 26 H 31 NO l7 , one of sugar series, was the form 
from which indigo-white was produced by oxidization. 
In 1877, M. Alvarez* attributed the formation of indigo to the 
action of bacteria, but in 1898 Breaudatf demonstrated that microbic 
life was not necessary. 
Marchlewski and Radclififej consider indican consists of sugar 
and a very unstable substance called indoxyl (C g H-X.O.). Prof. 
M. W. Beijerinck holds the view that the indigo producing plants 
may be divided into two groups, in one of which this substance 
exists as indican ( Indvjofera tinctoria and Polygonum tinctoria), 
while in the other (of which Woad, I satis tinctoria , is the type) 
it exists as indoxyl. More recently, however, Beijerinck § || has 
come to the conclusion that even indoxyl does not exist ready 
formed in Woad, but that it exists as a “loose compound” isatan, 
which by an enzyme isatase also present in Woad is easily decom- 
posed into indoxyl. 
Be this as it may, it is not difficult to extract indigo bine from 
fresh Woad leaves by the process given by Beijerinck. This 
consists in packing fresh Woad leaves into a stoppered bottle and 
tilling the bottle entirely with boiling water : inserting the stopper 
so that no air bubble is left between it and the top of the water : 
after a few hours the infusion will be found of a pale yellow colour, 
having, when cold, a green fluorescence. If an alkali be added to 
this infusion and air blown through it, indigo blue is precipitated 
on the further addition of an acid. Woollen articles dipped into 
this alkalised infusion, become on exposure to the atmosphere a pale 
azure blue. This change, however, takes place far more rapidly if 
they be dipped into acidulated water. The indigo thus obtained is, 
however, very apt to contain impurities ; notably, to pass into 
* Mods. Alvarez. ‘ Comptes rendus,’ vol. 105, p. 287, 18S7. 
f Breaudat L. “Sur le mode de formation de l’indigo,” ‘ Annales d'Hvgiene 
et de Medicine Coloniales,’ vol. i, 1898, No. 4, Oct. -Nov., p. 535. 
I Marchlewski and Radcliffe. ‘Journal of the Society of Chemical Industry,’ 
1898, p. 443. 
§ Beijerinck M. W., loc. cit. “Further researches on the formation of 
Indigo from Woad.” June 30th, 1900. 
|| Beijerinck M. W., loc. cit. “ On Indigo formation.” Mar. 31st, 1900. 
