115 
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 de- 
nounced 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 fer- 
ments with the appearance of whitish grey buhbles, 
afterwards these become blue, and finally a deep me- 
tallic 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 cop- 
peras and an excess of lime or alkaline water. The 
oxygen of the indigo then comhines with the pro- 
toxide 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 satu- 
rated, 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 ad- 
vantage 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 sub 
stance, 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 sub 
stance “ 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 univer- 
sally well known, and are foüowed with but trifling 
variations in different provinces and different manu- 
factories. 
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 im- 
proved, 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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