428 On Indigo. 
the same as by Bergman, but differing con- 
siderably in the proportions. Indeed it is 
most probable that tbe foreign matters will 
be found to differ materially both in quan- 
tity and kind, from the various modes and 
circumstances. of the manufacture as prac- 
tised in different places, and perhaps from 
the various species of plants from which the 
indigo is extracted in different parts of the 
world. 
It is to be understood that the part called 
pure Indigo is the sole colouring matter, and 
that which gives value to the article. The 
rest may be considered as dross, doing no 
good, and being probably harmless to the 
use of the drug as a dye, but scarcely so to 
the printer, who meets with obstructions 
enow in the exercise of his art, without in- 
troducing such as may easily be avoided. 
When we consider, however, that indigo 
is produced by a species of fermentation from 
vegetable matter, analogous to the vinous 
and acetous fermentation of saccharine mat- 
ter, it is not improbable that the fermentation 
in many cases may be incomplete. And as 
the foreign matter found in the indigo of 
commerce is chiefly vegetable, and composed 
of the same elements as pure indigo, it may 
by a fresh fermentation develope more of the 
