INDIGO. 319 



it suspended, the agitation is stopped, and the grain 

 slowly subsides. The same degree of nicety is re- 

 quired 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 suf- 

 fered 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 

 discharged 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 application of fire 

 he^it. 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 which 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 j and, for this last reason, the Ha- 



