148 
wood in contact with the bottom of the dish ; as 
long as the colour of the wood remains unaltered, 
the heat is not too high ; but when the wood begins 
to be charred, the process must be stopped. A 
small quantity of water will, perhaps, remain in the 
soil even after this operation, but it always affords 
useful comparative results ; and if a higher temper- 
ature were employed, the vegetable or animal mat- 
ter would undergo decomposition, and in conse- 
quence the experiment be wholly unsatisfactory. 
The loss of weight in the process should be 
carefully noted, and when in four hundred grains 
of soil it reaches as high as 50, the soil may be 
considered as in the greatest degree absorbent, 
and retentive of water, and will generally be found 
to contain much vegetable or animal matter, or a 
large proportion of aluminous earth. When the 
loss is only from 20 to 10, the land may be con- 
sidered as only slightly absorbent and retentive, 
and siliceous earth probably forms the greatest 
part of it. 
2. None of the loose stones, gravel, or large 
vegetable fibres, should be divided from the pure 
soil till after the water is drawn off; for these 
bodies are themselves often highly absorbent and re- 
tentive, and, in consequence, influence the fertility 
of the land. The next process, however, after that 
of heating, should be their separation, which may 
be easily accomplished by the sieve, after the soil 
has been gently bruised in a mortar. The weights 
of the vegetable fibres or wood, and of the gravel 
and stones, should be separately noted down, and 
the nature of the last ascertained ; if calcareous, 
