of soil on
which it is used. Experience has shewn that its effects are most
beneficial on light and deep sandy soils, but that on heavy retentive
clays it is without effect, or even absolutely injurious. In clay soils
it is important to use every means of getting rid of moisture, and any
plan which adds 200 or 300 tons of water to them, only aggravates their
natural defects to an extent which more than counterbalances the
benefits derived from the manurial matter it contains. Whatever the
ultimate result of the use of town sewage in the liquid form may be, it
is unlikely that it will be employed in general agricultural practice.
It is more probable that it will be found necessary to set apart a
certain breadth of land to be treated by it exclusively. Many plans have
been proposed for conveying it through considerable districts, and
selling to the surrounding farmers the quantities which they require,
but wherever large sewage-works are established, it will be impossible
to depend on a precarious demand, and the promoters of such schemes will
be compelled, as part of their speculation, to supply not only the
manure, but the land on which it is to be used. Indeed, the difficulties
attending the whole question are so formidable, that even those who are
most anxious to see a stop put to the waste of manurial matter must
admit that the prospect of a successful economic result is not
encouraging. Nor is it likely that anything will be done until the whole
system of managing town refuse is changed, and in place of deluging it
with water, some plan can be contrived which, while fulfilling sanatory
requirements, shall preserve it in a concentrated form, or convert it
into a dry and inodorous substance.

FOOTNOTES:

[Footnote L: Report on the economic uses of peat. Highland Society's
Transactions, N.S., vol. iv. p. 549.]

CHAPTER IX.

COMPOSITION AND PROPERTIES OF VEGETABLE MANURES.

Many vegetable substances have been employed as manures, either alone or
as auxiliaries to farm-yard manure. Like that substance, they are
general manures, and contain all the constituents of ordinary crops;
but, owing to the absence of animal matter, they in general undergo
decomposition and fermentation much more slowly, although some of them
contain a so largely preponderating proportion of nitrogen, that they
may in some respects be compared to the strictly nitrogenous manures.

_Rape-dust, Mustard, Cotton and Castor Cake._--Rape-