these compounds are
destroyed by burning, the bases remain united to carbonic acid.

5.--_Chemical Changes that occur in the formation of Peat._ When a plant
perishes, its conversion into humus usually begins at once. When exposed
to the atmosphere, the oxygen of the air attacks it, uniting with its
carbon producing carbonic acid gas, and with its hydrogen generating
water. This action goes on, though slowly, even at some depth under
water, because the latter dissolves oxygen from the air in small
quantity,[2] and constantly resupplies itself as rapidly as the gas is
consumed.

Whether exposed to the air or not, the organic matter suffers internal
decomposition, and portions of its elements assume the gaseous or liquid
form. We have seen that ripe peat is 10 to 12 _per cent._ richer in
carbon and equally poorer in oxygen, than the vegetable matters from
which it originates. Organic matters, in passing into peat, lose carbon
and nitrogen; but they lose oxygen more rapidly than the other two
elements, and hence the latter become relatively more abundant. The loss
of hydrogen is such that its proportion to the other elements is but
little altered.

The bodies that separate from the decomposing vegetable matter are
carbonic acid gas, carburetted hydrogen (marsh gas), nitrogen gas, and
water.

Carbonic acid is the most abundant gaseous product of the peaty
decomposition. Since it contains nearly 73 _per cent._ of oxygen and but
27 _per cent._ of carbon, it is obvious that by its escape the
proportion of carbon in the residual mass is increased. In the formation
of water from the decaying matters, 1 part of hydrogen carries off 8
parts of oxygen, and this change increases the proportion of carbon and
of hydrogen. Marsh gas consists of one part of hydrogen to three of
carbon, but it is evolved in comparatively small quantity, and hence has
no effect in diminishing the _per cent._ of carbon.

The gas that bubbles up through the water of a peat-bog, especially if
the decomposing matters at the bottom be stirred, consists largely of
marsh gas and nitrogen, often with but a small proportion of carbonic
acid. Thus Websky found in gas from a peat-bed

Carbonic acid 2.97
Marsh gas 43.36
Nitrogen 53.67
------
100.00

Carbonic acid, however, dissolves to a considerable extent in water, and
is furthermore absorbed by the living vegetation, which is not true of
marsh gas