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 salæratus. Potash has many uses in agriculture.
1. It forms a constituent 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?