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slacked lime, on exposure to a gentle heat, with fre- 

 quent stirrings of the fluid, a fresh fermentation takes 

 place, a blue froth rises to the surface, and the liquor, 

 though it appears itself of a reddish colour, dyes 

 woollen of a green colour, which, like that from 

 indigo, changes to a blue, as soon as exposed to the 

 atmosphere. Its nature is very similar to that of 

 indigo in every respect, and experiments have been 

 made which prove the identity of their colouring 

 matter. If the woad plant be prepared like the 

 indigofera, indigo will be afforded, though in a much 

 less proportion than that obtained from the exotic 

 plant. 



The average produce from an acre of land is about 

 one ton of woad ; in very favourable seasons some- 

 times one and a half ton are obtained. It requires 

 change of soil ; the best land is injured by being sown 

 more than twice successively with woad. It is im- 

 ported into England at rather a heavy impost duty of 

 3s. per cwt., its price being from 18s. to 20s. the cwt. 



The number of vegetable substances used by us 

 for dyeing blue is very cirumscribed, indigo and woad 

 being the only two which are of extensive adoption. 

 A few others may be enumerated, but these are of 

 little importance. 



2 G 



