Part 3 (1/2)

POTASH.

[How may we obtain potash from ashes?

What are some of its agricultural uses?]

When we pour water over wood ashes it dissolves the _potash_ which they contain, and carries it through in solution. This solution is called _ley_, and if it be boiled to dryness it leaves a solid substance from which pure potash may be made. Potash left exposed to the air absorbs carbonic acid and becomes carbonate of potash, or _pearlash_; if another atom of carbonic acid be added, it becomes super-carbonate of potash, or _salaeratus_. Potash has many uses in agriculture.

1. It forms a const.i.tuent of nearly all plants.

2. It unites with silica (a neutral), and forms a compound which water can dissolve and carry into the roots of plants; thus supplying them with an ingredient which gives them much of their strength.[D]

3. It is a strong agent in the decomposition of vegetable matter, and is thus of much importance in preparing manures.

4. It roughens the smooth round particles of sandy soils, and prevents their compacting, as they are often liable to do.

5. It is also of use in killing certain kinds of insects, and, when artificially applied, in smoothing the bark of fruit trees.

The source from which this and the other inorganic matters required are to be obtained, will be fully considered in the section on manures.

SODA.

[Where is soda found most largely?

What is Glauber's salts?

What is was.h.i.+ng soda?

What are some of the uses of lime?]

_Soda_, one of the alkalies contained in the ashes of plants, is very much the same as potash in its agricultural character. Its uses are the same as those of potash--before enumerated. Soda exists very largely in nature, as it forms an important part of common salt, whether in the ocean or in those inland deposits known as rock salt. When combined with sulphuric acid it forms sulphate of soda or _Glauber's salts_. In combination with carbonic acid, as carbonate of soda, it forms the common was.h.i.+ng soda of the shops. It is often necessary to render soils fertile.

LIME.

_Lime_ is in many ways important in agriculture:

1. It is a const.i.tuent of plants and animals.

2. It a.s.sists in the decomposition of vegetable matter in the soil.

3. It corrects the acidity[E] of sour soils.

4. As chloride or sulphate of lime it is a good absorbent of fertilizing gases.

[How is caustic lime made?

How much carbonic acid is thus liberated?

How does man resemble Sinbad the sailor?]