15 
and carbonic acid, and the composition of this latter 
gas, seem to be determined with so much accuracy, 
we can have no difficulty in estimating the actual 
quantity of carbon which growing seeds afford in a 
given time, if we know the quantity of oxygen gas 
that is consumed : for as the bulk of acid produced 
is exactly equal to that of oxygen lost, the quantity 
of carbon given out by the seeds will be indicated by 
the excess of the weight of this acid gas over that of 
the oxygen. Thus in the experiment already related 
(8.), twelve peas were put into ajar with 16.5 cubic 
inches of air, of which 3.46 inches were oxygen gas. 
By the fourth day, the whole of this oxygen was con- 
sumed, and the radicles of the seeds were about an 
inch in length. Now, as 3.46 cubic inches of carbo- 
nic acid were likewise produced, which contain O.465, 
or rather less than half a grain of carbon, such may 
be considered to be the quantity of that substance 
furnished by these twelve peas in four days ; or one 
pea, in that time, yielded 0.039 of a grain of carbon. 
Hence the quantity of carbon yielded by seeds, before 
they become capable of replacing it by absorption 
from the soil, is extremely small. Dr Thomson ob- 
serves, that, from a good many trials, made with as 
much care as possible, the quantity of carbon sepa- 
rated, during the whole process of malting, by the 
formation of carbonic acid gas, does not exceed two 
per cent *. 
221. With respect to the mode in which the car- 
bon of the seed unites with the oxygen gas of the 
* Syst. Chem. vol. v. p. 446. 3d edit. 
