Although ammonia is a gas and pervades the atmosphere, few, if any, plants can take it up, as they do carbonic acid, through their leaves. It must all enter through the roots in solution in the water which goes to form the sap. Although the amount received from the atmosphere is of great importance, there are few cases where artificial applications are not beneficial. The value of farm-yard and other animal manures, depends chiefly on the ammonia which they yield on decomposition. This subject, also the means for retaining in the soil the ammoniacal parts of fertilizing matters, will be fully considered in the section on manures.
Can plants use more ammonia than is received from the atmosphere?
On what does the value of animal manure chiefly depend?
What changes take place after ammonia enters the plant?
May the same atom of nitrogen perform many different offices?
After ammonia has entered the plant it may be decomposed, its hydrogen sent off, and its nitrogen retained to answer the purposes of growth. The changes which nitrogen undergoes, from plants to animals, or, by decomposition, to the form of ammonia in the atmosphere, are as varied as those of carbon and the constituents of water. The same little atom of nitrogen may one year form a part of a plant, and the next become a constituent of an animal, or, with the decomposed dead animal, may form a part of the soil. If the animal should fall into the sea he may become food for fishes, and our atom of nitrogen may form a part of a fish. That fish may be eaten by a larger one, or at death may become food for the whale, through the marine insect, on which it feeds. After the abstraction of the oil from the whale, the nitrogen may, by the putrefaction of his remains, be united to hydrogen, form ammonia, and escape into the atmosphere. From here it may be brought to the soil by rains, and enter into the composition of a plant, from which, could its parts speak as it lies on our table, it could tell us a wonderful tale of travels, and assure us that, after wandering about in all sorts of places, it had returned to us the same little atom of nitrogen which we had owned twenty years before, and which for thousands of years had been continually going through its changes.
Is the same true of the other constituents of plants?
Is any atom of matter ever lost?
The same is true of any of the organic or inorganic constituents of plants. They are performing their natural offices, or are lying in the earth, or floating in the atmosphere, ready to be lent to any of their legitimate uses, sure again to be returned to their starting point.
Thus no atom of matter is ever lost. It may change its place, but it remains for ever as a part of the capital of nature.
CHAPTER IV
What are ashes called?
How many kinds of matter are there in the ashes of plants?
Into what three classes may they be divided?
What takes place when alkalies and acids are brought together?
We will now examine the ashes left after burning vegetable substances. This we have called inorganic matter, and it is obtained from the soil. Organic matter, although forming so large a part of the plant, we have seen to consist of four different substances. The inorganic portion, on the contrary, although forming so small a part, consists of no less than nine or ten different kinds of matter.2 These we will consider in order. In their relations to agriculture they may be divided into three classes—alkalies, acids, and neutrals.3
Is the character of a compound the same as that of its constituents?
Give an instance of this.
Do neutrals combine with other substances?
Name the four alkalies found in the ashes of plants.
Alkalies and acids are of opposite properties, and when brought together they unite and neutralize each other, forming compounds which are neither alkaline nor acid in their character. Thus, carbonic acid (a gas,) unites with lime—a burning, caustic substance—and forms marble, which is a hard tasteless stone. Alkalies and acids are characterized by their desire to unite with each other, and the compounds thus formed have many and various properties, so that the characters of the constituents give no indication of the character of the compound. For instance, lime causes the gases of animal manure to escape, while sulphate of lime (a compound of sulphuric acid and lime) produces an opposite effect, and prevents their escape.
The substances coming under the signification of neutrals, are less affected by the laws of combination, still they often combine feebly with other substances, and some of the resultant compounds are of great importance to agriculture.
The alkalies which are found in the ashes of plants are four in number; they are potash, soda, lime and magnesia.
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 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.4
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.
Where is soda found most largely?
What is Glauber's salts?
What is washing 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 washing soda of the shops. It is often necessary to render soils fertile.
Lime is in many ways important in agriculture:
1. It is a constituent of plants and animals.
2. It assists in the decomposition of vegetable matter in the soil.
3. It corrects the acidity5 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