356 



INDIGO. 



dye-stuff. In tliis he enumerates and dilates on the different works 

 and treatises, to the number of about twenty, which had been published 

 up to that date. 



The greater proportion of the indigos of India are prepared from 

 Indigofera tinctoria, which is extensively cultivated for that purpose, 

 in Bengal and other provinces from the 20° to the 30° N. lat., and in 

 Tinnivelly, Madras. There are two processes for manufacturing the 

 dye-stuff : one the dry leaf, and the other the green leaf process. The 

 latter is considered the best, and is in most common use. It is as 

 follows. When the plant begins to flower, it is cut down at about six 

 inches from the ground, and carried to the steeping vats with as little 

 delay as possible, strewn horizontally in the vats and pressed down 

 by means of beams fixed into side posts, bamboos being placed under 

 the beams. Water is immediately run in, just sufficient to cover the 

 plant. If water is not at once let in, the plant w^ill heat, and become 

 spoilt. The time for steeping depends much on the temperature of 

 the atmosphere, and can only be learnt by experience and careful 

 watching of the vats, but in close sultry weather, with the thermo- 

 meter at 96° in the shade, eleven or twelve hours are sufficient. In 

 cooler weather, fifteen or sixteen hours are requisite. If the plant 

 is very ripe, the vat will be ready earlier than if the plants were 

 young and unripe. The following are indications that the vat is ready 

 to let off : 



1. As soon as the water begins to fall in the vat. 



2. When the bubbles that rise to the surface burst at once. 



3. On splashing up the surface water it has an orange tinge 

 mingling with the green. 



4. The smell of the water. When ripe, it should have a sweetish, 

 pungent odour, quite different from the raw smell of the unripe green- 

 coloured water. 



About seven men enter the vat and agitate it, either by the hands 

 or with a wooden paddle, at first gently, but gradually increasing as 

 the fecula begins to separate, which is known by the subsidence of 

 the froth, and the change of the colour of the water from green to 

 dark blue. The time necessary for this beating process is generally 

 from IJ to 3 hours. 



The following tests may be employed to ascertain if the heating 

 has been sufficient. 



1. Take a little of the water in a saucer and let it stand. If the 

 fecula subsides readily, and the water remains of a Madeira wine 

 colour, the beating may be stopped. 



2. Dip a coarse cloth in the vat, and wring out the water, observing 

 the colour. If green, the beating must be continued, but if a brownish 

 colour, it is ready. 



3. When sufficiently beaten, the surface of the water will, as soon 

 as the beating is suspended, become of a peculiar glassy appearance, 

 and the froth will subside with a sparkle and effervescence like 

 champagne. 



Three or four chatties of cold water or weak lime water are then 

 sprinkled over the surface, to hasten the precipitation of the fecula, 

 which does not completely take place in less than three or four hours. 

 The water is drawn off from the surface through plug holes in the 



