in the soil.

"An explanation, however plausible, can hardly be accepted as correct,
if based mainly on data, which, although highly probable, are not proved
to be based on fact. In chemical inquiries, especially, nothing must be
taken for granted, that has not been proved by direct experiment. The
following questions naturally suggest themselves in reference to this
subject: What is the amount of nitrogen in soils of different
characters? What is the amount more particularly after a good, and after
an indifferent crop of clover? Why is the amount of nitrogen in soils,
larger after clover, than after wheat and other crops? Is the nitrogen
present in a condition in which it is available and useful to wheat? And
lastly, are there any other circumstances, apart from the supply of
nitrogenous matter in the soil, which help to account for the beneficial
effects of clover as a preparatory crop for wheat?

"In order to throw some light on these questions, and, if possible, to
give distinct answers to at least some of them, I, years ago, when
residing at Cirencester, began a series of experiments; and more
recently, I have been fortunate enough to obtain the co-operation of Mr.
Robert Valentine, of Leighton Buzzard, who kindly undertook to supply me
with materials for my analysis.

"My first experiments were made on a thin, calcareous, clay soil,
resting on oolitic limestone, and producing generally a fair crop of
red-clover. The clover-field formed the slope of a rather steep hillock,
and varied much in depth. At the top of the hill, the soil became very
stony at a depth of four inches, so that it could only with difficulty
be excavated to a depth of six inches, when the bare limestone-rock made
its appearance. At the bottom of the field the soil was much deeper, and
the clover stronger, than at the upper part. On the brow of the hill,
where the clover appeared to be strong, a square yard was measured out;
and at a little distance off, where the clover was very bad, a second
square yard was measured; in both plots, the soil being taken up to a
depth of six inches. The soil, where the clover was good, may be
distinguished from the other, by being marked as No. 1, and that where
it was bad, as No. 2.

CLOVER-SOIL NO. 1. (GOOD CLOVER).

"The roots having first been shaken out to free them as much as possible
from the soil, were then washed once or twice with cold distilled water,
and, after having been dried for a little w