18 
GLEANINGS IN SCIENCE. 
altered in quantity during the experiment, and the -eigt of the oxygen absorb 
was ascertained from that of the water which had owing results. 
Four exueriments conducted in this mannei , yielded t it _ p; x p t . 
647« 
1.22 , 
49 
Expt. S 
845 5 
2.00 
6.8 
29.4 
Expt. 
5500 
0.82 
2.9 
28.2 
3 Expt. 
5166 
0.84 
3.9 
21.5 
25.0 
Weight of liquid grains. 
Weight of oxygen absorbed, 
Weight of Indigo collected, 
Proportion of oxygen in ( 
Making 1 au°aver.ige of 26 per cent, of oxygen absorbed ; a quantity nearly double 
whtt Crum supposes °to exfst in pure I JL, and an average between hat wh£ 
he ascribes to Cerulin and Phenicin- It is, however, little more than the half of 
what Thompson states in his analysis. 
There is hardly anv occasion to seek a nearer concurrence between experiments 
made in the manner 'just 4escribed on the liquid ol the vats ; because the 1" < 
forms but a very small proportion of the matter held in solution therein, pud it is 
very possible that the other ingredients may also absorb oxygen, especially when 
the ptitrirl fermentation commences. 
Jt is evident, however, that a further analysis of pure Indigo m the dry way is a 
very desirable object. It seems to have escaped the attention of Gay-Lussac and 
Thenard, and latterly of Marcet and of Dr. Prout, in their Researches upon the 
Constituents of Vegetable Compounds. ^ 
It is worth while in this place to mention a fact observed in the course of these 
experiments, namely, that where a slight excess of potash is mixed with the vat 
liquid, the Indigo formed remains in sole]' m, and passes through the filter with 
ease, leaving the precipitated extractive matter behind. This blue solution will 
keep for any time, and does not deposit its Indigo even in the open air but as 
soon as the alkali is saturated by an acid, it immediately precipitates, leaving the 
liquid colourless. If the dose of potash be not sufficient to throw down all the 
yellow matter, the solution retains a green colour, and cloth dipped into it takes 
a green dye. When hung up to dry, however, the mixed action becomes evident ; 
for the d'ye remains fixed in the lower part of the cloth, while the yellow, more 
perfectly dissolved, spreads \vith the liquid to the upper part which was not dyed. 
There is no reason to believe in this case,' that the air changed the colour from 
green to blue, although such may be true of the dyer’s vat -liquid • 
The quantity of Indigo deposited /icr se from 1000 parts of yellow liquid of the 
specific gravity 1003.1, varied but little, and may be estimated at 0*7o parts* 
In practice, a vat of 637 cubic feet is considered to yield a good produce at 16 seers, 
which is as nearly as possible 0-75 per 1000 of liquid. The common produce of 
the vats in this part of the country does not exceed 0.5, or one five thousandth of. 
their weight of Indigo. 
But when potash, lime, or other prec.ipitants are employed, the weight of the 
Indigo is much increased ; not, as experiment proves, from an increase of the actu- 
al produce, nor from any union of the precipitant with the Indigo, but from its 
causing the deposition of another matter, to which I have given the name of yellow 
or brown extract. 
To obtain this yellow extract in an insulated state* 10,000 grains of mother liquid 
were evaporated to dryness : a solid residue was in one case collected, weighing 
47 grains. With another liquor it was 20 grains heavier ; and in the experiment 
made on a small scale with the leaves, where the fermentation continued for 24 hours, 
the same weight of mother liquor yielded 246 grains of residue- As this element 
cf the plant seems to he so variable, and as it must evidently produce much influ- 
ence in the manufacture* it is probably one of the chief causes of the nicety usual 
in timing the fermentation, and of tiie variable tendency of the Indigo to preci- 
pitate in the beating vat. The dried extract has a dark brown colour and vitreous 
surface similar to that of dried gluten, or the brown extract of toast-water : it has 
a peculiar, not unpleasant smell, and rather a bitter taste : it deliquesces in a damp 
atmosphere, and dissolves in water, which it dyes of a deep brown or lustre. Al- 
though the original mother liquor is exceedingly liable to ferment and become pu- 
trid, the brown matter undergoes no change, either when kept dry, or in a mois- 
tened state 
It is precipitated from its aqueous solution l>y potash, soda, ammonia, lime, 
anq their carbonates; by infusion of galls, acetate of lead, and nitrate of silver. 
4 be acids, and prussiate of potash, did not affect it; but the action of reagents was 
not investigated in detail. & 
