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LECTURE VII. 
ON MANURES OF MINERAL ORIGIN, OR FOSSILE MANURES * 
THEIR PREPARATION, AND THE MANNER IN WHICH THEY 
ACT. - — OF LIME IN ITS DIFFERENT STATES J OPERATION 
OF LIME AS A MANURE AND A CEMENT; DIFFERENT COM- 
BINATIONS OF LIME.— -OF GYPSUM; IDEAS RESPECTING 
ITS USE. — -OF OTHER NEUTRO-SALINE COMPOUNDS, EM- 
PLOYED AS MANURES. — OF ALKALIES AND ALKALINE 
SALTS ; OF COMMON SALT. 
The whole tenour of the preceding Lectures shows, 
that a great variety of substances contributes to 
the growth of plants, and supplies the materials of 
their nourishment. The conversion of matter that 
has belonged to living structures into organised 
forms is a process that can be easily understood ; 
but it is more difficult to follow those operations by 
which earthy and saline matters are consolidated 
in the fibre of plants, and by which they are made 
subservient to their functions. Some enquirers 
adopting that sublime generalization of the ancient 
philosophers, that matter is the same in essence, 
and that the different substances considered as 
elements by chemists, are merely different arrange- 
ments of the same indestructible particles, have 
endeavoured to prove, that all the varieties of the 
principles found in plants, may be formed from the 
substances in the atmosphere ; and that vegetable 
