To the politeness of Dr. William Dunbar, a planter of Mississippi, the
author is indebted for many important papers relating to this region,
formerly in the possession of his father--a gentleman well known to the
philosophic world as the author of several valuable scientific papers
upon the natural history and meteorology of this country. Among the
manuscripts of this gentleman in the author's possession, is the
following account of the manufacture of Indigo, written by himself, then
an extensive indigo planter, near New-Orleans.
"The reservoir water in or near the field where the indigo plant is
cultivated, is prepared, in lower Louisiana, by digging a canal from
eighty to one hundred feet long, and 25 or 30 feet wide. The plant is in
its strength when in full blossom: it is then cut down, and disposed
regularly in a wooden or brick vault, about ten feet square, and three
feet deep; water is then poured or pumped over it until the plant is
covered; it is suffered to remain until it has undergone a fermentation,
analogous to the vinous fermentation. If it stands too long, a second
fermentation commences, bearing affinity to the acetous fermentation:
your liquor is then spoiled, and will yield you but little matter of a
bad quality--sometimes none at all. The great difficulty is to know this
proper point of fermentation, which cannot sometimes be ascertained to
any degree of certainty; when the plant is rich, and the weather warm, a
tolerable judgment may be formed by the ascent or swelling of the liquor
in the vat; at other times no alteration is observed. But to return; the
liquor is at length drawn off into another vat, called the beater; it
may remain in the first vat, called the steeper, from ten to fifteen
hours, and even twenty-four hours, in the cool weather of autumn. The
liquor is agitated in the beater in a manner similar to the churning of
butter; when first drawn off, it is of a pale straw colour, but
gradually turns to a pale green, from thence to a deeper green, and at
length to a deep blue. This is occasioned by the grains of indigo, at
first dissolved in the water, and afterward extricated by beating. The
indigo is now ready to fall to the bottom by its superior specific
gravity; but a precipitant is often used to cause a more hasty
decomposition, and consequent precipitation. This is effected most
powerfully by lime-water, but it may also be done by any mucilaginous
substance, as the juice of the wild mallows, purslain, leaves of the
elm-tree, and of many others indigenous in this country. The saliva
produces the same effects. A few hours after the precipitation, the
water standing above the indigo is drawn off by holes perforated for
that purpose; the indigo matter is then swept out and farther drained,
either by putting it in bags of Russia duck, or more commodiously in
wooden cases with a bottom of cloth; after which it is put in a wooden
frame, with a loose Osnaburg cloth between it and the frame, and
subjected to a considerable press--light at first, but heavy at the
last; and when solid enough, cut into squares, which shrink up in drying
to half their first bulk. After it appears to be dry, it is put up in
heaps to sweat and dry the second time; it is then fit for market. All
that has not been injured by missing the true point of fermentation,
sells here generally at a dollar a pound. The planter often, by mistake,
makes his indigo of a superior quality, so as to be equal to the
Guatemala indigo, and be worth from one dollar and a quarter to two
dollars. This happens from the indigo maker's drawing off his water from
the steeper too soon, before it has arrived at its due point of
fermentation. In this case the quantity is so much lessened, as by no
means to render the planter compensated by the superior quality. The
grand desideratum to bring the making of indigo to some degree of
certainty, is the discovery of some chymical test, that shall
demonstrate the passing of the liquor from the first to the second
fermentation. This test will probably be discovered in some saline body,
but which, or in what quantity, it is yet difficult to ascertain."