1000 parts of distilled water
dissolved out from different soils from one half to one and a half parts
of soluble constituents; or from .05 to .15 per cent. Of this soluble
matter from 30 to 67 per cent is mineral in its nature, and from 33 to
70 per cent organic. Poor sandy soils yield the minimum quantity, while
peaty soils yield the maximum. The quantity of soluble matter in a
regular peaty soil may vary from .4 to 1.4 per cent; this consists
chiefly, however, of organic matter. (See Johnson's 'How Crops Feed,' p.
312.)

Perhaps a more satisfactory method is by analysing the drainage-water of
a soil. This has been found to vary very considerably in composition.
The average of a large number of analyses are .04 to .05 per cent of
dissolved matter. Of this dissolved matter the largest proportion is
made up of organic matter, nitric acid, lime, and soda salts. It must be
borne in mind, however, that even the drainage-water does not furnish an
exact indication of the amount of dissolved matter in a soil. Much,
perhaps the largest proportion of dissolved matter, never finds its way
into the drainage-water. That contained by the drainage-water really
represents the surplus quantity of dissolved matter which the soil is
unable to retain, and which is thus washed by the rain into the drains.
The composition of drainage-water is interesting, as it shows that,
practically speaking, all the necessary plant ingredients are in a state
of solution in the soil.

NOTE VI. (p. 90).

CHEMICAL COMPOSITION OF THE SOIL.

The most important substances present in soils are as follows: silica,
alumina, lime, magnesia, potash, soda, ferric oxide, manganese oxide,
sulphuric acid, phosphoric acid, and chlorine. Of these substances the
presence of alumina, silica, lime, and, in certain cases, magnesia,
along with the organic portion of the soil--the humus--has the chief
influence in determining the nature and the physical properties of a
soil.

In order to clearly understand to what it is soils owe the nature of
their chemical composition, it is necessary to consider the composition
of some of the chief minerals out of the disintegration of which soils
are formed.

While we know of some seventy elements present in the earth's crust, it
is practically made up of only some sixteen. These sixteen are--oxygen,
silicon, carbon, sulphur, hydrogen, chlorine, phosphorus, iron,
aluminium, calcium, magnesium, sodium, potassium, fluorine, mangan