336 VEGETABLE SUBSTANCES. 



is then formed into solid balls, which are pressed into 

 a compact substance in wooden moulds. These 

 balls are dried upon hurdles; if exposed to the suri 

 they turn black on the outside, but in a sheltered 

 place they become of a yellowish hue. Dealers in 

 this commodity usually prefer the first, though it is 

 said that there is really no material difference between 

 the two descriptions. Good balls are distinguished by 

 their superior weight, and by exhibiting, on being 

 rubbed, a violet colour within. 



These balls require a farther preparation before they 

 can be converted to the purpose of dyeing. They are 

 first beaten with wooden mallets on a brick or stone 

 floor, until they are reduced to a coarse powder. This 

 is heaped up into the middle of the apartment to 

 the height of about four feet, space being left to allow 

 a sufficient passage round the sides; it is then 

 moistened with water, which speedily induces fer- 

 mentation, and thick fetid fumes are emitted. The 

 heap is daily moistened and stirred about with shovels, 

 for the space of twelve days, after which period it is 

 moved less frequently, and without being watered. 

 At length it is made into a heap for the dyer. Dr. 

 Bancroft observes, that the proper mode of conduct- 

 ing the fermentation, and the exact time at which it 

 ought to be stopped, still remain so uncertain that 

 those who make it their business to prepare woad 

 have no decided facts or indications to govern their 

 management in this respect; and the goodness of 

 any particular quantity can never be ascertained other- 

 wise than by actual use. The powder thus prepared' 

 gives only brownish tinctures, of different shades, 

 to aqueous, spirituous, or alkaline menstrua ; rubbed 

 on paper it communicates a green stain. If the 

 powder be diluted with boiling water and allowed to 

 stand for some hours in a close vessel, then, with the 

 addition of about one-twentieth of its weight of newly 



