Chlorine is an important ingredient of vegetable ashes, and is often required to restore the balance to the soil. It is not found alone in nature, but is always in combination with other substances. Its most important compound is with sodium, forming chloride of sodium (or common salt). Sodium is the base of soda, and common salt is usually the best source from which to obtain both soda and chlorine. Chlorine unites with lime and forms chloride of lime, which is much used to absorb the unpleasant odors of decaying matters, and in this character it is of use in the treatment of manures.
OXIDE OF IRON.
Oxide of iron, one of the constituents of ashes, is common iron rust. Iron itself is naturally of a grayish color, but when exposed to the atmosphere, it readily absorbs oxygen and forms a reddish compound. It is in this form that it usually exists in nature, and many soils as well as the red sandstones are colored by it. It is seldom, if ever, necessary to apply this as a manure, there being usually enough of it in the soil.
This red oxide of iron, of which we have been speaking, is called by chemists the peroxide. There is another compound which contains less oxygen than this, and is called the protoxide of iron, which is poisonous to plants. When it exists in the soil it is necessary to use such means of cultivation as shall expose it to the atmosphere and allow it to take up more oxygen and become the peroxide. The black scales which fly from hot iron when struck by the blacksmith's hammer are protoxide of iron.
The peroxide of iron is a very good absorbent of ammonia, and consequently, as will be hereafter described, adds to the fertility of the soil.
What can you say of the oxide of manganese?
How do you classify the inorganic constituents?
Oxide of Manganese, though often found in small quantities in the ashes of cultivated plants, cannot be considered indispensable.
Having now examined all of the materials from which the ashes of plants are formed,[F] we are enabled to classify them in a simple manner, so that they may be recollected. They are as follows:—
| ALKALIES. | ACIDS. | NEUTRALS. |
| Potash. | Sulphuric acid. | Silica. |
| Soda. | Phosphoric " | Chlorine. |
| Lime. | Oxide of Iron. | |
| Magnesia. | " Manganese. |