INDIGO. 
periority, it is usually advantageous to culti- 
vate the other, because it is heavier. The 
first will grow in many different soils ; the 
second succeeds best in those which are 
most exposed to the rain. Both are liable 
to great accidents. Sometimes the plant 
becomes dry, and is destroyed by an insect 
frequently found on it ; at other times, the 
leaves, which are the valuable part of the 
plant, are devoured in the space of twenty- 
four hours by caterpillars. This last mis- 
fortune, which is but too common, has 
given occasion to the saying, “ that the 
planters of indigo go to bed rich, and rise 
in the morning totally ruined.” This pro- 
duction ought to be gathered in with great 
precaution, for fear of making the farina 
that lies on the leaves, and is very valuable, 
fall off by shaking it. When gathered, it is 
thrown into the steeping-vat, which is a 
large tub filled with water. Here it under- 
goes a fermentation, which in twenty-four 
hours at furthest is completed. A cock is 
then turned to let the water run into the 
second tub, called the mortar or pounding 
tub. The steeping-vat is then cleaned out, 
that fresh plants may be thrown in ; and 
thus the work is continued without inter- 
ruption. The water which has run into the 
pounding-tub is found impregnated with a 
very subtle earth, which alone constitutes 
the dregs or blue substance that is the ob- 
ject of this process, and which must be se- 
parated from the useless salt of the plant, 
because this makes the dregs swim on the 
surface. To effect this, the water is forcibly 
agitated with wooden buckets that are full 
of holes and fixed to a lpng handle. This 
part of the process requires the greatest 
precautions. If the agitation be disconti- 
nued too soon, the part that, is used in 
dying, not being sufficiently separated 
from the salt, would be lost. If, on the 
other hand, the dye were to be agitated too 
long after the complete separation, the 
parts would be brought together again, and 
form a new combination ; and the salt re- 
acting on the dregs would excite a second 
fermentation, that would alfer the dye, 
spoil its colour, and make what is called 
burnt indigo. These accidents are prevent- 
ed by a close attention to the least altera- 
tions that the dye undergoes, and by the 
precaution which the workmen take to draw 
out a little of it from time to time in a clean 
vessel. When they perceive that the co- 
loured particles collect by separating from 
the rest of the liquor, they leave off shaking 
the buckets in order to allow time to the 
blue dregs to precipitate to the bottom of 
the tub, where they are left to settle till 
the Water is quite clear. Holes made in 
the tub, at different heights, are then open- 
ed one after another, and this useless water 
is let out. The blue dregs remaining at the 
bottom having acquired the consistence of a 
thick muddy liquid, cocks are then opened, 
which draw it off into the settler. After it 
is still more cleared of much superfluous 
water in this third and last tub, it is drained 
into sacks ; from whence, when water no 
longer filters through the cloth, this matter 
now. becomes of a thicker consistence, and 
is put into chests, where it entirely loses its 
moisture. At the end of three months the 
indigo is fit for sale. 
It is used, in washing, to give a bluish co- 
lour to linen : painters also employ it in 
their water-colours ; and dyers cannot 
make fine blue without indigo. The an- 
cients procured it from the East Indies ; in 
modern times it has been transplanted into 
America. The cultivation of it, successively 
attempted at different places, appears to be 
fixed at Carolina, St. Domingo, and Mexico. 
That which is known under the name of 
Guatimala indigo, from whence it comes, is 
the most perfect of all. 
Indigo may be obtained from the merium 
tinctorium, and the isatis tinctoria or woad ; 
a plant cultivated and even found wild in 
England. When arrived at maturity, this 
plant is cut down, washed, dried hastily in 
the sun, ground in a mill, placed in heaps, 
and allowed to ferment for a fortnight. It is 
then well mixed, and made up into balls, 
which are piled upon each other, and ex- 
posed to the wind and sun. In this state 
they become hot, and exhale a putrid am- 
maniacal smell. The fermentation is pro- 
moted, if necessary, by sprinkling the balls 
with water. When it has continued for a 
sufficient time, the woad is allowed to fall 
to a coarse powder ; in which state it is 
sold as a dye-stuff. By treating woad 
nearly in the same manner with the indigo- 
fera, indigo has been obtained from it by 
different chemists. 
Indigo is a soft powder, of a deep blue, 
without either taste or smell. It under- 
goes no change, though kept exposed to the 
air. Water, unless kept long upon it, does 
not dissolve any part of it, nor produce any 
change. When heat is applied to indigo, it 
emits a bluish red smoke, and at last burns 
away with a very faint white flame, leaving 
behind it the earthy parts in the state of 
ashes. Neither oxygen nor the simple com- 
