SOILS, MANURES, &c. 251 
nitrous acid of the air, and thereby 
rendered the foil fruitful; the operation 
of the falts became fo confiderably extern- 
live by the walhing of rains, and the 
attrabiion of the acid in the foil. 
Good marie would undoubtedly have 
produced confequences nearly fimilar to 
the above, but none could be conve¬ 
niently procured ; there can be no doubt 
that the foil on the furface contained oily 
particles in abundance, but the alkalis 
were wanting to form' the faponaceous 
mucilage. 
Fixed vegetable alkali is produced by 
incineration, or the burning of vegetables 
in the open air, till their acids and oils 
be difcharged, or volatilized, and their 
allies become white, or nearly fo. The 
falts thus produced are never pure, 
but conlift of different proportions of 
alkali’s and neutrals, according to the 
nature 
