EXTRACTION OF INDIGO FROM WOAD. 311 



first, this being repeated till no more indigo can be ob- 

 tained from the deposit. 



Nothing more is necessary to be done to the paste of 

 indigo when it has been freed from all foreign substances, 

 than to separate from it the water which renders it of the 

 consistency of porridge ; and for this purpose I shall pro- 

 pose a method which I have practised successfully in some 

 analogous operations. Line the inside of a basket with a 

 coarse bag of woollen or tow cloth, throw the paste into 

 the bag, and leave it to drain. When filtration is ended, 

 cover the paste with the upper end of the bag, which had 

 been turned down, and place upon it a large round wooden 

 dish, which will fit the inside of the basket, and upon this 

 put a weight, which is to be gradually increased till the 

 fecula acquires a great degree of closeness of texture : 

 if the operation be well performed, the mass can scarcely 

 be broken by the hand. This cake is afterwards cut into 

 squares, and dried at a temperature of between 30° and 

 40°. (Probably of Reaumur, and equal to 99° and 122^ 

 of Fahrenheit.) The preparation of indigo is afterwards 

 terminated by an operation which is called sweating. 



M. de Puymaurin states, that the most favorable time 

 for operation is when, ^^ upon breaking an angle of one of 

 the cubes, a dry noise is hearrV^ When this is the case, 

 the cakes of indigo are put into a large barrel till it is 

 full, when the top is covered, without having the head 

 fastened in. The indigo remains in this cask three weeks, 

 during which time it heats and gives out a disagreeable 

 odor, it transpires a portion of water, and becomes covered 

 with a white down. At the end of the specified time the 

 surface of the indigo is rubbed and smoothed, and it is 

 then prepared for sale. 



The indigo of woad, if prepared with all the care here 

 described, is equal, if not superior to the best of that 

 brought from Guatimala; its effects are the same in dy- 

 ing, and it differs from that neither in nature nor in char- 

 acteristics. By the manufacture of this kind of indigo in 

 France, a new source of agricultural prosperity may be 

 bestowed upon her. 



It now only remains to be determined whether or not 

 the farmer can with advantage turn his attention to the 

 manufacture of woad-indigo ; for without this, though the 

 discovery of the possibility of extracting indigo from the 

 isatis would be in itself an important one, it would be of 

 no use to the nation. 



