(K_{2}SO_{4}, MgSO_{4}, 6H_{2}O), pure
_potassium magnesium sulphate_.

NOTE II. (p. 217).

The quantity of potash obtainable from various plants in the manufacture
of potashes on a large scale is illustrated by the following statements.
1000 lb. of the following vegetative products yield the following
quantities of potashes:--

lb.
Old spruce-wood 1/2
Old poplar-wood 3/4
Old oak-wood 1-1/2
Corn-stalks 17-1/2
Bean-stalks 20
Grape-vine twigs 40

(Storer, 'Agricultural Chemistry,' vol. ii. p. 108.)

PART III.

MANURES

CHAPTER VII.

FARMYARD MANURE

Farmyard manure is the oldest, and is still undoubtedly the most
popular, of all manures. It has stood the test of long experience, and
has proved its position as one of the most important of all our
fertilisers. It is highly desirable, therefore, to make a somewhat
detailed examination of its composition, and to see on what the
variation in this depends; and, finally, to examine into the mode of its
action as a manure.

That it should prove a valuable manure is scarcely to be wondered at, as
it is originally formed from vegetable substance, and as it therefore
contains all the elements present in the plant itself.

Its composition is very variable, and probably no two samples would
yield exactly similar analyses. In this fact lies one of the chief
difficulties of the treatment of the subject, and all statements made
in the following pages as to its chemical composition must be taken as
only _approximate_.

We may divide its constituents into three classes.

1. That portion due to _solid excreta_.

2. The liquid portion, largely made up of dilute _urine_.

3. The _straw_, or other material, which is used as litter.

The composition of the manure will vary according to the proportion in
which these three substances are present, as well as according to the
composition of the substances themselves. It will consequently tend to a
clearer apprehension of the subject if we first examine briefly the
chemical composition of the solid excreta and urine of the farm animals.

1. _Solid Excreta._

The manurial value of the solid excreta of animals--_i.e._, the
proportion they contain of _nitrogen_, _phosphoric acid_, and
_potash_--depends on a variety of conditions.

The solid excreta of horses, sheep, cows, and pigs, are well kn