INDIGO,

45i

carry on operations in a somewhat similar manner, but working on a smallscale, do not succeed so well, and the quality of their produce is inferior.The average quantity of indigo annually made in the Bengal Presidencyamounts to about 4 millions of kilos.

M. Twist* states that in the Guzerata country the leaves of the indigoshrubs are dried in the sun, and next steeped for four or five days in purewater, previously poured into well-made tanks, care being taken to stir themixture occasionally. The liquid is run off from the tanks after lapse of theabove time ; and, after having deposited the indigo as a semi-fluid mass, thesupernatant clear liquid is slowly run off; and the indigo having been thrownon to a coarsely-made but thick and tightly-woven woollen cloth, is left todrain, and next dried in the sun. The natives of the above-named countryare in the habit of adding to the yet pasty mass some blue mineral, or clay.

The Chinese cut the plants in the manner above described, and treatthem further in the same way as already mentioned; but they add powderedslaked lime to the mass in the fermenting tanks, thereby causing a more rapiddeposition of the precipitate afterwards. The Chinese also dry the indigo inthe sun, according to some authors.f It is rather doubtful whether the state-ment concerning the drying of indigo exposed to sunlight is quite correct.

M. Kcechlin-Schwartz relates what he has seen during a journey and lengthysojourn in Bengal; and he was told that the exclusion of sunlight is absolutelynecessary to ensure good produce ; yet a great many authors, among themthose named in the foot-note below, speak of drying in the sun, which, asregards Twist, is a communication made from personal inspection on thespot. From private communication made to us by a Java indigo planter wecan reconcile these discordant statements; the faCt is, that as long as theindigo is still soft and pasty, so that it can easily receive impressions from thefinger, it is kept in the shade, and almost in the dark, being merely exposedto strong ventilation ; but as soon as the mass has become dry and sufficientlysolid to bear handling, it is further dried during the daytime in open air, beingplaced upon hurdles made of bamboo, and purposely exposed to the sun, pro-vided there be no danger of rain. This proceeding is also carried on in Bengal,but is very frequently there done not at the factory, but at or near Calcutta,and has therefore been overlooked by M. Koechlin-Schwartz, who has alsoforgotten to mention the care taken with regard to the boxes, as above specified,in which the indigo is sent over to Europe. The faCt is, that the ware ispacked for sea transport, chiefly at Calcutta, being sent thither from thefactories, when fit for handling though not quite dry, in light bamboo baskets,as kindly communicated to us by Mr. J. A. Longridge, C.E., who hastravelled in India while on Government duty as Inspector and Reporteron Railways. The process of indigo manufacture in America and the WestIndies is similar to that already described. In southern China, and especiallyin Kouang-si, Kouang-toung, and Fo-kien, indigo is largely produced for homeconsumption only.

We have now to consider the theory of this process of manufacture. Thefollowing questions arise :—What are the chemical phenomena observed during

* “ Descriptio Guzerata j” a very rare book.

t Sloane, Gaertncr, Lamarck, Plagne (“ Annales Maritimes,” 1825). Vilmorin, “ Journald Agriculture Pratique,” i., 449. Hervy, “ Journal de Pharmacie,” xxvi., 290.

2 G 2