INDIGO. 289 



having attained its due pitch, and beginning 

 to abate, the operator lets off the liquor by 

 a cock into another vat, called the beater, the 

 mortar, or the pounding-tub. The gross 

 matter is taken for manure, and the steeping- 

 vat cleansed for the reception of fresh plants, 

 as long as the harvest continues. 



The liquor that has run into the beating- 

 tub is found strongly impregnated with a 

 very subtile earth, which alone constitutes 

 the blue substance required. To separate 

 this from the useless salt of the plant, which 

 makes it float on the surface, the liquor is 

 agitated by incessant beating with bottomless 

 buckets full of holes and fixed to long han- 

 dles, until it heats, froths, and rises above the 

 rim of the vessel which contains it. To allay 

 this violent fermentation, oil is thrown in, 

 which instantly causes it to subside. This 

 part of the process requires the greatest pre- 

 caution, for if the agitation be discontinued 

 too soon, the part that is used in dyeing, not 

 being sufficiently separated from the salt, 

 would be lost. If, on the contrary, the dye 

 were to be agitated too long after the com- 

 plete separation, the parts would be brought 

 together again and form a new combination; 

 and the salt re-acting on the dregs would ex- 



VOL. I. U 



