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INDIGO.
Indigofera linctoria.
The history of the commerce of this substance
would be eminently interesting, but it is not possible
to enter on tbe subject here; suffice it to say, that
on its first introduetion into Europe it was almost
driven out by the bitter intolerance of persons whose
object was to prevent tbe old-fashioned woad (then
in use as much as indigo is now) from being driven
out before it. In 1557, at Frankfort, it was denounced
by the Germanic diet as the “ devil’s dye,”
and its use forbidden. The prohibition was repeated
in 1603; and as late as 1654, by imperial edict at
Ratisbon, the proscription was enforced. In England
an Act was made in Elizabeth’s time, authorising
the seizure and destruction of the offensive substance,
as well as the detention of persons possessing it. The
Act continued in force tili the reign of Charles II.,
and “ Brazil wood ” shared the odium with it.
Indigo is known to chemists under two forms—
white indigo (indigogene) and blue indigo, the latter
being only an oxydized state of tbe former. The
blue colour is entirely due to the oxygen, or at least
comes to the substance as it gets access to the oxygen
of the air; this is observable in the vats. Wlien the
fermented liquor or infusion of the plant first ferments
with the appearance of whitish grey buhbles,
afterwards these become blue, and finally a deep metallic
lustred purple red. Dyed cotton, when just
taken out of the dyeing vat, appears green, but
rapidly assumes its deep blue tone from contact with
the air. Blue indigo is perfectly insoluble in water,
but it is found that it is so only so long as it retains
its excess atom of oxygen. If it can be induced to
part with that, the remaining indigogene is soluhle
in an excess of sulphate of lime, or rather alkali.
Hence, for cotton dyeing, the vat is prepared by
grinding up a quantity of indigo with water to the
consistency of eream, and then mixing it with copperas
and an excess of lime or alkaline water. The
oxygen of the indigo then comhines with the protoxide
of iron in copperas to form oxide, and then
the deoxidized indigo readily combines with the lime
water, forming a yellowish green liquid, into which
the fabric to be dyed is plunged; and then, on heing
taken out and exposed to the air, the oxygen returns
to the solution with which the fabric has been saturated,
and the deep blue is restored and hecomes
permanent without the use of any mordants. The
dye applied in this manner is used cold. According
to the plan adopted by native dyers, “chunäm,”
“ sajji ” (crude potash), and “ gurh ” (molasses),
form the solvent and deoxidizing agents; otherwise
the process is identical. They do not use copperas,
though they have it in plenty in the form of “ lüra
kasis,” or “kalü safed.” Wool and silk are not
dyed in this way, but in another manner, taking advantage
of another property of indigo. Pure indigo
is soluble in sulphuric acid, but the solution is thick
and black. This has been called caruleo sulphuric
acid, sulphindylic acid, &c. (“ murabba ” in Urdu),
because it has the nature of both the indigo and the
aeid, neither undergoing the slightest change in itself.
This latter suhstance is not a sulphate of indigo, that
would imply a Chemical combination between the
acid and the dye, and the formation of a new substance,
hut it is not so. The acid and indigo comhine,
but neither is changed. This solution is capable,
however, of destruction by an excess of caustic alkali,
and turns by it to a yellow colour, from which
nothing will restore it.
This sulphindylic acid is principally employed in
dyeing wool and silk, and the excess acid is removed
by washing in alkali.
Chemically pure indigo is of specific gravity 1 '50,
and possesses neither taste nor smell; it is a substance
“ indifferent,” having neither acid nor basic
properties. Good indigo is known by its fine purple
blue colour, and by its fracture, which when rubbed
with a hard smootli substance exhihits a coppery
red lustre. No remarks need here be added on the
manufacture of indigo. The ordinary processes of
fermentation, of drawing off the liquor, of heating,
and of collecting the “fecula,” or precipitate of
indigo from the liquor and pressing it, are universally
well known, and are foüowed with but trifling
variations in different provinces and different manufactories.
The main points appear to he, the watching the
soaking plants so as to be able to tap off the infused
liquor exactly at the right point of fermentation, and
next, to beat the liquor in the second vat exactly
long enough. No doubt in these points the native
manufacturers in this province are as yet eminently
deficient. Knowledge of these things can only be
acquired by careful observation and long experience.
Another point is, that the “fecula” is much improved,
after being collected, by being boiled in
copperas, and then pressed into its boxes.
Indigo manfactured by simply collecting the fecula,
and dropping it down in cakes to harden in the sun,
is termed “gaud indigo.”—(Baden Powell’s “Punjab
Products.”
826. Indigo. Local Committee. Berar.
1,587. Indigo. Dr. G. Bidie. Madras.
5,238. Indigo. Bombay Committee.
3,052. Indigo. India Museum, London.
ANIMAL DYES.
Bombay Committee.
63 & 64. Coccus cacti. (Two samples.)
65. Coccus lacca, or Kade lakh.
66. Lac dye, or Potti abta.
Mysore Local Committee.
10!). Cochineal. Bangalore.
Jardine, Skinner, Sf Co.
3,648. Lac dye.
India Museum, London.
Peoree, or Püree (Indian yellow). Monghyr.
Amritsar Local Committee.
161. Peori, or Indian yellow.
158. Lak dana (lac dye).
159. Kirm dana (cochineal).
India Museum, London.
Lac dye. Coccus lacca, Linn. Komb-arruk, B.
Mirzapore.
Do. Calcutta.
Do. Jubbulpore.
Do. Bengal.
The quantity of Lac dye exported from India
during the official year 1871-2 was 23,236 cwts.,
valued at 8,14,450 Rupees.
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