y2 -Dr. Austin’s Experiments ,. &c. 
three elementary airs are prefent, and, being expelled by heat 
from the metals with which they were combined, unite with 
each other, and form fixed air. It is not material to the pre- 
fent argument, whether the light inflammable air be fuppofed 
to be furnifhed from water, or from the regulus of a metal: 
it is enough for our purpofe, that none of the fubftances em- 
ployed in thefe experiments, contain heavy inflammable air or 
charcoal, in fufficient quantity to account for the fixed air pro- 
duced, as Dr. Priestley * has juftly obferved. 
The growth of plants affords a ftrong proof of the forma- 
tion of charcoal from the fubftances which have been affigned. 
If we may believe experiments, water and air alone are ne- 
ceflary to this natural procefs ; yet vegetation is the great fource 
of charcoal or heavy inflammable air. This enquiry is ftill in 
its infancy ; but from the beft experiments that have been made 
it fhould feern, that plants grow beft in phlogifticated air ; that 
they take in phlogifticated air, and give out dephlogifticated air. 
Thefe phenomena cannot be accounted for but by luppofing, 
that water Is decompofed by growing plants; that part of its 
dephlogifticated air is difcharged into the atmofphere ; and that 
the other conftituent part of water, with phlogifticated air, is 
taken into the growing fubftance. Thus the phlogifticated 
and light inflammable airs are brought together by the procefs 
of vegetation. 
O 
* Priestley, VI. p* 3*9* 
