210 
On Indigo. 
[July 
of richness, lias a specific gravity not appreciably higher than that of distilled 
water, and affords out of 1000 parts, by weight, not more than 3 parts of indigo- 
blue, and nearly the same quantity of carbonate of liine, equivalent to about a 
grain and a half of quicklime in 1000 of the liquid; which is the proportion in 
common lime water. 
If that yellow liquor be introduced into a glass globe, with a graduated stem, 
previously" filled with hydrogen, by plunging the vessel into the vat, we may 
transfer a portion of deoxydised indigo conveniently to the mercurial pneumatic 
trough, and measure the "quantity of oxygen which a given bulk of it absorbs in 
becoming blue 3 . The quantity will be proportional to the strength and purity of the 
vat liquor. I have lately instituted a series of experiments, the results of which 
will, I hope, prove interesting, in reference to the problem for determining the qua- 
lity or purity, and strength of different commercial indigoes ; but they are not yet 
mature enough to meet the public eye. The rigid inode of examining this drnsr is 
to eliminate the indigo-blue from the other substances, by the readiest artifices 
of analysis, and to weigh it apart. It may be objected to the analysis of indigo, 
that it is too complex and operose a process to be practicable with the dispatch 
and to the extent which the public quarterly sales of indigo require. But I con- 
ceive this to he a mistake. When only one object is pursued, various arrange- 
ments may be readily contrived for attaining it. Under this conviction I ven- 
tured to state, ten years ago, in the introduction to the first edition of my Dic- 
tionary of Chemistry, that “ the result of numerous researches made with that 
view, has shewn me the possibility of rendering analysis, in general, a much easier, 
quicker, and more certain operation, than it seems hitherto to have been in ordi- 
nary hands.” My experience since has fully justified that statement. 
Accordingly, about three years ago, I suggested to the Honourable Court of 
Directors of the East India Company, the propriety of establishing an assay office 
for indigo in Calcutta, to guide them in their purchases of that article, and to en- 
lighten the manufacturers in Bengal about the value of their various products and 
processes ; I again submitted to their consideration, last autumn, a memorial 
to the same effect, in which I detailed the advantages likely to accrue from such 
establishment to indigo-planters, dealers or brokers, and consumers. But the 
Court did not think it expedient at present to make any alteration in their indigo 
department. How much an office of this kind is wanted in London, in con- 
nexion with the quarterly sales of indigo, the following series of analyses, lately 
executed by myself, will sufficiently demonstrate. The quantity of indigo required 
for the assay need never exceed ten grains, provided a very delicate assay balance 
be employed ; and by a suitable system of arrangements, the average quality of 
500 chests may be accurately determined in the course of a day, by a diligent 
chemist, with four or six ordinary assistants to follow his directions. 
1. East-Indian Indigoes ; prices as at the last October Sales: 
Price. Description. Real Indigo 
s. d . in 100 parts. 
Lundy, very low quality, .. ..29 
Low, pale, Oude, .. not determined. 
Middling, ordinary Madras, . . .. 37 5 
Middling, ordinary Oude, .. .. 27-75 
Good, Oude, .. ..54 
Broken, middling, r. viol, dull viol, and lean, .. 46 
Ditto, a little being coppery viol, and cop. .. .. 565 
Good Madras, ,, ..60 
Broken, middling viol, and cop. viol, spotted, . . 42 
Much broken and very small, very crumbly and limy, soft, good 
violet, 75 
Large broken, and square, even, middling r. viol. .. 54.5 
Very fine Madras, .. .. 58 
Square and large broken, § middling viol, and V gd. cop. viol. .. 60 
Large broken, very good ; paste, a little limy, gd. viol. .. 70 
Square and large broken, gd. rd. viol. .. 66.6 
Ditto, soft, fine paste, fine viol. .. ..60 
Ditto, tine purple and blue, . . .*.75 
cedi.^ a , P ‘ ap . er on .? n 1 di 8 , o> published in our first number, and republished in 
absorLd «^ ber ° f i the . ^ uarteriy Journal, this method of measuring the 
employed, with some necessary precautions how 1 L *' 
was at vauunce with Dr. Ure’s analysis. — E. *G1. 
1 
2 
2 
2 
3 
3 
3 
3 
3 
4 
4 
4 
4 
5 
6 
6 
7 
9 
9 
3 
4 
3 
3 
6 
9 
2 
3 
3 
9 
3 
0 
6 
0 
lever ; 
but 
the pre- 
oxygen 
the result 
