EXTRACTION OP INDIGO FROM WOAD. 307 



a thin, greenish, and iridescent pellicle. When in this 

 state, the liquor is to be drawn off into the receiving tub, 

 and changed from that into the beating-vessel. 



In both methods, it is necessary to precipitate the indigo 

 which is held in solution or in suspension in the water ; 

 and this operation, which is called beetling or beating, is 

 needed to give to the indigo the blue color which belongs 

 to it. 



There are two methods of beating which are practised, 

 one being applicable to the liquor obtained by infusion, 

 and the other to that procured by fermentation. I shall 

 here describe both of them. 



As soon as the heat of the liquor, which has been passed 

 through the leaves in the manner described in the first 

 process, has fallen to between 120° and 111° Fahrenheit, 

 beating is commenced. The instrument employed for this 

 purpose is a broom, or a handful of willow twigs from which 

 the bark has been peeled. With this the liquor is forcibly 

 agitated, the quickness of the motion being gradually 

 lessened as the infusion cools. 



As soon as a white foam rises upon the top, beating is 

 suspended, but is resumed again as soon as the foam sub- 

 sides, and assumes a fine blue color. If the liquor is too hot, 

 or has been too much beaten, the blue borders upon the 

 violet ; otherwise it is the color of the sky. Beating is 

 continued at intervals, allowing the foam to exhibit its 

 color. When by rest it appears only of a pale blue, the 

 beating Is continued without any interruption. When the 

 foam remains white, or changes to a reddish color, the 

 operation draws to a close. 



By beating, the color of the water, which was that of 

 white wine, becomes more and more brown. The beating 

 is ended, when upon pouring the liquor into a glass vessel, it 

 appears of a uniform brown. Should a tinge of bluish green 

 be perceived near the sides of the glass, the beating must be 

 continued. Upon the whole, it is better to beat it too much 

 than too little. The time requisite for performing the 

 operation upon the liquor drawn from three hundred pounds 

 of leaves, is generally about an hour and a half. 



When the liquor is at length left undisturbed, the indigo 

 is deposited in grains at the bottom of the bucket. Eight 

 or ten hours are sufficient for this purpose. The liquor is 

 then to be drawn oif and the indigo dried, in order that all 

 the water which could cause it to ferment may be separat- 

 ed from it. 



