marl,[6]
old mortar, leached ashes and peat ashes, (for in all these it is the
chief and most "alkaline" ingredient,) is recommended to compost with
peat. Let us inquire whether carbonate of lime can really exert any
noticeable influence in improving the fertilizing quality of peat.

In the case of vitriol peats, carbonate of lime is the cheapest and most
appropriate means of destroying the noxious sulphate of protoxide of
iron, and correcting their deleterious quality. When carbonate of lime
is brought in contact with sulphate of protoxide of iron, the two bodies
mutually decompose, with formation of sulphate of lime (gypsum) and
carbonate of protoxide of iron. The latter substance absorbs oxygen from
the air with the utmost avidity, and passes into the peroxide of iron,
which is entirely inert.

The admixture of any earthy matter with peat, will facilitate its
decomposition, and make it more active chemically, in so far as it
promotes the separation of the particles of the peat from each other,
and the consequent access of air. This benefit may well amount to
something when we add to peat one-fifth of its bulk of marl or leached
ashes, but the question comes up: Do these insoluble mild alkalies exert
any direct action? Would not as much soil of any kind be equally
efficacious, by promoting to an equal degree the contact of oxygen from
the atmosphere?

There are two ways in which carbonate of lime may exert a chemical
action on the organic matters of peat. Carbonate of lime, itself, in the
forms we have mentioned, is commonly called insoluble in water. It is,
however, soluble to a very slight extent; it dissolves, namely, in about
30,000 times its weight of pure water. It is nearly thirty times more
soluble in water saturated with carbonic acid; and this solution has
distinct alkaline characters. Since the water contained in a heap of
peat must be considerably impregnated with carbonic acid, it follows
that when carbonate of lime is present, the latter must form a
solution, very dilute indeed, but still capable of some direct effect on
the organic matters of the peat, when it acts through a long space of
time. Again, it is possible that the solution of carbonate of lime in
carbonic acid, may act to liberate some ammonia from the soluble
portions of the peat, and this ammonia may react on the remainder of the
peat to produce the same effects as it does in the case of a compost
made with animal matters.

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