GLEANINGS IN SCIENCE. 
id 
Sufficient has been adduced to prove, that whenever lime or the alkalies are 
tised iu the vat, the Indigo must be adulterated more or less with this substance ; 
and I suspect that the brown and green matters separated by Chevreui and others 
iu their analyses of Indigo, are attributable to this source. In an experimental 
wav, Indigo of a true dark green colour was easily collected, which weighed more 
than twice as much as the blue colour alone : it was also harder and more com- 
pact, and more liable to shrink and crack than the pure Indigo take; for besides 
the impuritv just described, there was always found a large proportion of earthy 
residue, on burning Indigo, where a precipitant was used, than where it was not ; 
the quantity was even as much as double or triple in amount* 
Carbonate of lime, alumine, and oxyde of iron, are the chief ingredients of 
the earthy residue, and I have seen them vary from five to nearly 50 per cent, of 
the Indigo : the last, as may be supposed, was merely refuse, and quite unsaleable. 
Carbonate of lime is seldom absent, for whatever lime may be in the plant or in 
the water is sure to be precipitated by the carbonic acid developed during the fer- 
mentation. Some manufacturers are in the habit of employing rain water pur- 
posely to avoid this source of adulteration, but it is doubtful whether the plant will 
not itself bring a portion of earths into solution. 
Upon the whole, it may be safely decided, that the purer the water is, and the 
cleaner and the more simply all the operations of the manufacture are conducted, 
the more beautiful and rich in colour will be the Indigo : arid it should be the 
first maxim of the planter, that it is purity, and not weight, which gives the value 
to his produce in the market. 
In conclusion of the present (Jesuitry notice, which will I hope at least serve 
the purpose of leading others to bestow further attention upon the subject, I an- 
nex an analysis of a specimen of Indigo, denominated fine blue in the Calcutta 
market, made in the year 11120, to which I have referred in a former part of this 
paper. 
Analysis of Calcutta Indigo. 
100 grains heated white in a closed platina crucible left a porous grey 
carbonaceous mass, with metallic lustre, weighing. — 49.0 
Burnt with access of air, the 49 grains were reduced to- — . ~ 7*42 
1.— 7 ? rumination of earthy Residue, 7*42. 
1. Boiled dry in nitric acid, and then digested in muriatic acid, 
a brown residue of oxyde of iron and alumine remained- — — 2.7 
2. From the solution, ammonia threw down alumine/——. 0.75 
Oxalate of ammonia — lime equal to-*-*—. 0.9 
3. The clear liquor evaporated left red oxyde of iron — 3.05 
2 — In the humid way. 
1. 100 Grains of Indigo digested in boiling water, some green and dark 
brown matter was dissolved, which when dry weighed 1.0 
2. Alcohol boiled over the remainder became of a bright claret colour, 
and yielded on evaporation a dark brown matter and a little yellow 
resin, weighings, , — .... 2.0 
3. Dilute muriatic acid then took up a mixture of greenish vegetable 
matter, and earths which were afterwards separated by burning. The 
green matter was thus found, — ~~ — — 7*2 
4. The Indigo now deemed pure weighed only - 79.5 
This sample of Indigo therefore was of the following composition. 
Oxyde of iron, — 5.75 
Alumine, — . 0-75 
Lime, . 090 
Green vegetable matter, 8 80 
Red or brown ditto,™ 2 00 
Pure Indigo,-—,.... — ~~ 79.50 
Loss, 2.30 
100.00 
P. 
