-----+--------+--------+--------+--------+--------
Silica | 65.72 | 65.00 | 67.99 | 68.23 | 62.70 | 63.51
Alumina | 18.57 | 18.64 | 19.61 | 18.30 | 23.80 | 23.09
Peroxide of iron | traces | 0.83 | 0.70 | 1.01 | 0.62 | none
Oxide of manganese | traces | 0.13 | none | none | none | none
Lime | 0.34 | 1.23 | 0.66 | 1.26 | 4.60 | 2.44
Magnesia | 0.10 | 1.03 | none | 0.51 | 0.02 | 0.77
Potash | 14.02 | 9.12 | none | 2.53 | 1.05 | 2.19
Soda. | 1.25 | 3.49 | 11.12 | 7.99 | 8.00 | 9.37
--------------------+--------+--------+--------+--------+--------+--------
| 100.00 | 99.47 | 100.08 | 99.83 | 100.79 | 101.37
--------------------+--------+--------+--------+--------+--------+--------

According as these various felspars are present in a soil, so will the
quality of the soil be. It stands to reason that as the presence of
potash in a soil is one of the distinguishing features of its fertility,
much will depend on the extent to which the orthoclase felspar is
present; and also, not only on the extent, but on the state and degree
of its disintegration. It is important to note the method of this
disintegration. It is effected by the absorption of water. This water is
not merely absorbed mechanically, but actually enters into the
composition of the mineral. It is not present as moisture merely,
capable of being expelled at ordinary boiling temperature, but it forms
what is known as water of composition. In this process of hydration, the
mineral loses its lustre and crystalline appearance, crumbles away into
a more or less--according to its state of disintegration--powdery mass.
A very great change is also effected in its chemical composition; it
loses nearly all its base. This is effected in the following way. As
water enters into the mineral's composition, it sets free a certain
portion of the base; there is thus formed a basic silicate, which, being
soluble in water, is washed away in solution. This change may be
illustrated by quoting the analysis of a kaolin clay formed by the
disintegration of orthoclase felspar.

_Kaolin Clay formed by disintegration of Orthoclase._

Silica 46.80
Alumina 36.83
Peroxide of iron 3.11
Carbonate of lime 0.55