502 



HISTORY OV THE VEUETABLE KINGDOM. 



removed from the house as soon as taken out. 

 The noxious odour of this refuse occasions the 

 peculiar unhealthiness incident to the occupa- 

 tion. 



As soon as the liquor is received into the 

 second vat, it is violently beaten by the repeated 

 fall of wooden buckets, full of holes, and fixed 

 to long handles moved by manual labour or 

 other power. A more complicated mechanical 

 contrivance is sometimes employed. This agita- 

 tion of the parts, by cliecking any farther fer- 

 mentation, prevents putridity, and especially 

 promotes the separation of the grain, as it is 

 technically called, or the dark coloured granular 

 pulp, which is the iudigo. Tlie whole of the 

 liquor and of the pulp change during the process 

 from green to deep blue. A large quantity of 

 air-bubbles are also expelled by the beating. 

 Lime-water is most usually added at this time, 

 ■ as it greatly assists in the formation of the grain. 

 When the grain, on being left in a quiescent 

 state for a brief period, separates readily from 

 tlie liquor which holds it suspended, the agita- 

 tion is stopped, and the grain slowly subsides. 

 The same degree of nicety is required to discover 

 the exact point for the cessation of agitation as 

 for determining that of fermentation. If too 

 little beaten, the grain will not be sufficiently 

 separated; if too nmch, a second fermentation 

 would be excited, which would alter the dye, 

 spoil its colour, and make what is called burnt 

 indigo. From time to time, therefore, a little is 

 drawn off and examined. 



When the grain is precipitated, the liquor 

 floating on the top is drawn off by means of 

 cocks, and suffered to run to waste; care being 

 taken to avoid mixing it with any brook or 

 cattle pond, as it contains poisonous qualities 

 vhich would be fatal to animals who might 

 drink it. The thick pulpy matter is then dis- 

 cliarged into the third or lowest vat, and after it 

 is still more disencumbered of supei-iluous water, 

 it is laded into common sacks. These are hung 

 up that the water may drain off', the indigo itself 

 being too thick to pass through. After draining 

 it is transferred to small wooden boxes, where 

 it is farther dried by exposure to alternate sun 

 and sliade. 



In the indigo factories of Bengal, some part 

 of the moisture is driven off by the direct appli- 

 cation of fire heat. This is done after the 

 colouring particles liave been separated from the 

 solution by beating. The indigo is then removed 

 from the agitation vat into a boiler, the bottom 

 only of which is of iron, while the sides are 

 built up of solid masonry. Of course only this 

 bottom can be exposed to tlie action of tlie fire, 

 by which circumstance the efficiency of the 

 vessel is importantly diminished; fuel is wasted, 

 because tliat portion of the heated air wliich 

 sJiouid apply to the sides, is prematurely drawn 



off into the chimney; time is lost, since the fluid 

 will necessarily impart to the masonry a portion 

 of the heat which it is made to imbibe; and, for 

 this last reason, the liability of the indigo to 

 the far greater evil of charring is much aug- 

 mented. If a better aiTangement were provided 

 for this purpose, the process would be materially 

 simplified, and might be carried farther than is 

 now consistent with prudence. , 



When the indigo is brought by this means to 

 that degree of consistence wliich is safely prac- 

 ticable, tlie thickened fecula is transferred to 

 largo cloths wherein the evaporation is further 

 continued by exposure to atmospheric influ- 

 ence. 



This intermediate operation of boiling is con- 

 sidered to be beneficial in arresting a second fer- 

 mentation of the fecula, to wliich it is sometimes 

 liable during the process of draining, wliile the 

 farther advantage is obtained of holding in solu- 

 tion the gummy and other matter unavoidably 

 extracted with the colouring matter. This 

 extraneous part thus passes off with the water, 

 and leaves the indigo in a purer state. The 

 superior quality of the Bengal indigo is attri- 

 buted to this method of preparation. 



If dried hastily in the sun it is apt to become 

 brittle. When all moisture is expelled, and the 

 substance is quite solid, it is cut into square 

 cakes. The process is not yet, however, com- 

 pleted. If exported in this state it would 

 speedily become mouldy; a second fennentation 

 is therefore necessary. To produce this the 

 cakes are heaped in a cask, and simply suffered 

 to remain there for about three weeks. During 

 this time they undergo s. degree of fermentation; 

 they become heated, moisture exudes from the 

 surface, a most disagreeable odour is emitted, 

 and finally the cakes are covered with a fine 

 white meal. They are then taken out and dried 

 in the shade for five or six days, when they are 

 in a fit state to be packed for exjiortation. 



The second method by scalding, instead of 

 fermentation, was first proposed for adoption by 

 Dr Roxburgh, and its great advantages over the 

 usual process were forcibly pointed out. The 

 method of obtaining the colouring matter, how- 

 ever, by boiling the plant was by no means the 

 invention of Dr Roxburgh, although that 

 gentleman has the merit of investigating scien- 

 tifically the peculiar nature <ind properties of 

 indigo, and of adopting and recommending a 

 treatment of it in accordance with his more 

 enlightened views on the subject. Tlie Hindoos 

 and the Egyptians both pursue this apparently 

 more simple process. 



In Egypt tlie plants are dried previously to 

 being put into an earthen jar with hot water. 

 Tliey are then worked witli a palm branch, in 

 the manner of churning, until the whole of the 

 colour is pressed out. Tli(t liquid is next strained 



