308 
MANUFACTURING INDIGO. 
Earthy parts soluble in acetic acid - 22 
Oxyde of iron soluble in muriatic acid - - 13 
Coloring parts almost pure - - » =47 
- .100 
There can not be a doubt that manufacturers 
of indigo might produce, by attending to the anal¬ 
ysis made by chemists, an article far superior to 
any hitherto offered to the public. It will also 
appear certain, when experience shall have con¬ 
firmed the value of a superior indigo, that a more 
than.remunerating price could be obtained for a 
purer article. For certain purposes a pure indigo 
would command double, and even treble prices, 
provided the supply were not too great for the con¬ 
sumption. This being the case, it would be well 
for our manufacturers to pay some attention to the 
subject, and endeavor, by some easy, unexpensive 
process, to bring it to as great perfection as possi¬ 
ble. To promote this object, I offer the following 
extracts and observations. 
Bergman dissolved, by means of ebullition in 
water, a ninth part of the weight of indigo. Qua- 
tremere also separated, by means of water, the 
parts which are soluble. He states their quantity 
to be more considerable, the worse the quality of 
the indigo; and that, after this operation, the resi¬ 
duum has acquired the qualities of the finest indi¬ 
go. He therefore proposes to purify what is of in¬ 
ferior quality, by boiling it in a bag, and renewing 
the water till it ceases to acquire color. 
If sulphuric acid be diluted with water, it at¬ 
tacks only the earthy matter that is blended with 
the indigo, and some mucilaginous ingredients. 
Muriatic acid digested or even boiled, with indi¬ 
go, takes up the earthy part, the iron, and a little 
extractive matter, which colors it yellowish brown, 
but without attacking in any manner the blue 
color. 
Acetic acid, commonly known as vinegar, ap¬ 
pears, by the table of contents, to take up a larger 
portion of impurities than any other acid, and be¬ 
ing at the same time the cheapest, I would recom¬ 
mend our indigo-makers to boil their pulp in vine¬ 
gar and water; by which process the whole mass 
will be superior to any indigo now offered in the 
market. 
It is evident from the analysis, that to make in¬ 
digo far superior to any now brought, to market, 
requires only an application of known facts to the 
art of making it. The following are well ascer¬ 
tained facts, that if indigo be boiled in water con¬ 
taining muriatic acid, twenty-five per cent, of the 
impurities contained in the best samples would be 
extracted, or if in vinegar and water thirty-four 
per cent. 
The best Bengal indigo, and I never remember 
it in a more depressed state, is worth, wholesale, 
one dollar eighty cents per pound. The average 
value of all the indigo imported from foreign coun¬ 
tries is about one dollar and fifteen cents per pound, 
while the average value of that made in the Uni¬ 
ted States is not more than fifty cents, and this 
great difference in the value is owing almost en¬ 
tirely to the great impurity of the article. The 
first object with our manufacturers, therefore, 
should be to make their indigo equal in quality to 
the best Bengal, and the second, to go as far be¬ 
yond them as is practicable. 
In the best samples of the indigo of this coun¬ 
try, there is evidently too much extractive matter, 
and there is no doubt that this- defect- arises, in a 
great measure, from their taking the pulp from 
the beater, instead of their running it into a vat 
of clear water, and after well agitating it there, 
letting it settle in the third vat. This third re¬ 
ceiver should undoubtedly be added where it has 
not been already done. Those manufacturers 
who would wish to avoid the' expense of a third 
receiver, may fill up the beater with fresh water, 
after drawing off the first liquor, and perform the 
operation in the same vat. 
The greatest improvement I can at present sug¬ 
gest, would be to boil the pulp taken from the 
vat by steam heat, for fifteen or twenty minutes, 
in water containing as much muriatic acid, or 
strong vinegar, as would give to the liquor a strong' 
acid taste. This operation can also be performed 
by placing a pipe in the beater from any steam 
vessel. 
Muriatic, or acetic acid, besides the oxyde of 
iron, dissolve the carbonate of lime, red resin, and 
alumina, contained in the indigo, and by being 
mixed with water, the. greater portion of the ex¬ 
tractive matter would be taken up at the same 
time. By boiling the pulp in water strongly im¬ 
pregnated with these acids, the indigo remaining 
would be from twenty-five to thirty-four per cent, 
better than any hitherto made, and a price, more 
than equivalent to the difference in the loss of 
weight and expense of working, would be obtained 
from the consumer. 
I have been informed by some South Carolina 
planters, that, owing to their inability to proceed 
with the fermentative operation as rapidly as the 
crops require, a portion is often left on the fields 
for two or three - weeks after the plants have arri¬ 
ved at maturity. This circumstance alone is suf¬ 
ficient-to blast the interest of the planters. Their 
interest would be much better consulted, by gath¬ 
ering in the crop, drying it, and extracting the 
coloring matter by the simmering process. This 
difficulty is obviated in Bengal by their planting 
the seed in successive periods, so that one crop 
shall ripen a week or more after the other, each 
crop being sufficient to supply one set of tanks du¬ 
ring the period of maturity. 
Dyers as well as indigo-planters would be high¬ 
ly benefited by attending to the analysis of indigo. 
Were they, when a superior color is wanted, to 
boil the ground indigo in a bag as described by 
Quatremere, there would be no difficulty of ob¬ 
taining the desired result from indigo of any quality. 
Of the two essential objections, stated by the 
late General Wade Hampton—the first, “ that cot-, 
ton paid better than indigo,” has been reversed by 
the great depression in the value of cotton. The 
second, “ that it injured the health of the negro,” 
tnay no doubt be easily obviated by precautionary 
means. The beating process is probably the sole 
cause of the unhealthiness of the manufacture. 
So rapid is the absorption of oxygen by the color¬ 
ing feculae, during the process of beating by the 
workmen, as to render the surrounding atmosphere 
