rudiments of knowledge on the subject are owing. 
About the year 1755, this celebrated professor 
proved, by the most decisive experiments, that 
limestone and all its modifications, marbles, chalks, 
and marles, consist principally of a peculiar earth, 
united to an aerial acid : that the acid is given 
out in burning, occasioning a loss of more than 
40 per cent., and that the lime in consequence 
becomes caustic. 
These important facts immediately applied with 
equal certainty, to the explanation of the uses of 
lime, both as a cement and as a manure. As a 
cement, lime, applied in its caustic state, acquires 
its hardness and durability, by absorbing the aerial 
(or, as it has been since called carbonic) acid, 
which always exists in small quantities in the at- 
mosphere ; it becomes, as it were, again limestone. 
Chalks, calcareous marles, or powdered lime- 
stones, act merely by forming an useful earthy 
ingredient of the soil, and their efficacy is propor- 
tioned to the deficiency of calcareous matter, 
which, in larger or smaller quantities, seems to be 
an essential ingredient of all fertile soils ; neces- 
sary, perhaps, to their proper texture, and as an 
ingredient in the organs of plants. 
Burnt lime, in its first effect, acts as a decomposing 
agent upon animal or vegetable matter, and seems 
to bring it into a state, in which it becomes more 
rapidly a vegetable nourishment ; gradually, how- 
ever, the line is neutralised by carbonic acid, and 
converted into a substance analagous to chalk ; 
but in this case, it more perfectly mixes with the 
other ingredients of the soil, is more generally 
