314 
Mr. Boys estimates that 266 0 bushels are the 
common produce of an acre of ground, which, 
according to his calculation, would give 17^900 lbs., 
containing 
Carbonate of lime - 69160 lbs. 
Gypsum - - 9509.5 
Oxide of iron - - 12967.5 
Saline matter - - 2593.5 
Charcoal - - 7780.5 
In this instance there was undoubtedly a very 
considerable quantity of matter capable of being 
active as manure produced in the operation of 
burning. The charcoal was very finely divided ; 
and exposed on a large surface on the field, must 
have been gradually converted into carbonic acid. 
And gypsum and oxide of iron, as I mentioned in 
the last Lecture, seem to produce the very best 
effects when applied to lands containing an excess 
of carbonate of lime. 
The second specimen was from a soil near Cole- 
orton, in Leicestershire, containing only four per 
cent, of carbonate of lime, and consisting of three- 
fourths light siliceous sand, and about one-fourth 
clay. This had been turf before burning, and 100 
parts of the ashes gave 
6 parts charcoal. 
3 Muriate of soda and sulphate of potash, 
with a trace of vegetable alkali. 
9 Oxide of iron. 
And the remainder the earths. 
In this instance, as in the other, finely divided 
charcoal was found; the solubility of which would 
be increased by the presence of the alkali. 
