502 



HISTOKY OF THE VEGETABLE 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 po\ver. A more complicated mechanical 

 contrivance is sometimes employed. This agita- 

 tion of the parts, by checking 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 indigo. The 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 

 the 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 much, 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 

 which would be fatal to animals who might 

 drink it. The thick pulpy matter is then dis- 

 charged into the third or lowest vat, and after it 

 is still more disencumbered of superfluous 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 shade. 



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 have 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 the action of the fire, 

 by A\hich circumstance, the efficiency of the 

 vessel is importantly diminished; fuel is wasted, 

 because that portion of the heated air which 

 should 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 gi-eater evil of charring is much aug- 

 mented. If a better arrangement were provided 

 for this pui-pose, the process would be materially 

 simplified, and might be can-ied farther than is 

 now consistent with prudence. 



When the indigo is brought by this means to 

 that degree of consistence which is safely prac- 

 ticable, the thickened fecula is transferred to 

 large 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 which it is sometimes 

 liable during the process of draining, while 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 fermentation 

 is therefore necessary. To produce this the 

 cakes ai-e heaped in a cask, and simply suffered 

 to remain there for about three weeks. During 

 this time they undergo a degree of fermentation; 

 the}' become heated, moisture exudes from tlie 

 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 exportation. 



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 and properties of 

 indigo, and of adopting and recommending a 

 treatment of it in accordance with his more 

 enlightened views on the subject. The Hindoos 

 and the Egyptians both pursue this apparently 

 more simple process. 



In Egypt the plants are dried previously to 

 being put into an earthen jar with hot water. 

 They are then worked with a palm branch, in 

 the manner of churning, until the whole of the 

 colour is pressed out. The liquid is next strained 



