CHAPTER III
HYDROGEN, OXYGEN AND NITROGEN
HYDROGEN AND OXYGEN
What is water composed of?
If analyzed, what does it yield?
How do plants obtain their hydrogen and oxygen?
Let us now consider the three gases, hydrogen, oxygen and nitrogen, which constitute the remainder of the organic part of plants.
Hydrogen and oxygen compose water, which, if analyzed, yields simply these two gases. Plants perform such analysis, and in this way are able to obtain a sufficient supply of these materials, as their sap is composed chiefly of water. Whenever vegetable matter is destroyed by burning, decay, or otherwise, its hydrogen and oxygen unite and form water, which is parted with usually in the form of an invisible vapor. The atmosphere of course contains greater or less quantities of watery vapor arising from this cause and from the evaporation of liquid water. This vapor condenses, forming rains, etc.
Hydrogen and oxygen are never taken into consideration in manuring lands, as they are so readily obtained from the water constituting the sap of the plant, and consequently should not occupy our attention in this book.
NITROGEN
If vegetable matter be destroyed, what becomes of these constituents?
What is the remaining organic constituent?
Why is it worthy of close attention?
Do plants appropriate the nitrogen of the atmosphere?
Nitrogen, the only remaining organic constituent of vegetable matter, is for many reasons worthy of close attention.
1. It is necessary to the growth and perfection of all cultivated plants.
2. It is necessary to the formation of animal muscle.
3. It is often deficient in the soil.
4. It is liable to be easily lost from manures.
Although about four fifths of atmospheric air are pure nitrogen, it is almost certain that plants get no nutriment at all from this source. It is all obtained from some of its compounds, chiefly from the one called ammonia. Nitric acid is also a source from which plants may obtain nitrogen, though to the farmer of less importance than ammonia.
AMMONIA
What is the principal source from which they obtain nitrogen?
What is ammonia?
How is it formed?
Where does it always exist?
How do plants take up ammonia?
Ammonia is composed of nitrogen and hydrogen. It has a pungent smell and is familiarly known as hartshorn. The same odor is perceptible around stables and other places where animal matter is decomposing. All animal muscle, certain parts of plants, and other organized substances, consist of compounds containing nitrogen. When these compounds undergo combustion, or are in any manner decomposed, the nitrogen which they contain usually unites with hydrogen, and forms ammonia. In consequence of this the atmosphere always contains more or less of this gas, arising from the decay, etc., which is continually going on all over the world.
This ammonia in the atmosphere is the capital stock to which all plants, not artificially manured, must look for their supply of nitrogen. As they can take up ammonia only through their roots, we must discover some means by which it may be conveyed from the atmosphere to the soil.
Does water absorb it?
What is spirits of hartshorn?
Why is this power of water important in agriculture?
What instance may be cited to prove this?
Water may be made to absorb many times its bulk of this gas, and water with which it comes in contact will immediately take it up. Spirits of hartshorn is merely water through which ammonia has been passed until it is saturated.1 This power of water has a direct application to agriculture, because the water constituting rains, dews, &c., absorbs the ammonia which the decomposition of nitrogenous matter had sent into the atmosphere, and we find that all rain, snow and dew, contain ammonia. This fact may be chemically proved in various ways, and is perceptible in the common operations of nature. Every person must have noticed that when a summer's shower falls on the plants in a flower garden, they commence their growth with fresh vigor while the blossoms become larger and more richly colored. This effect cannot be produced by watering with spring water, unless it be previously mixed with ammonia, in which case the result will be the same.
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
INORGANIC MATTER
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.
ALKALIES
The alkalies which are found in the ashes of plants are four in number; they are potash, soda, lime and magnesia.
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 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.
SODA
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
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 does man resemble Sinbad the sailor?
In nature it usually exists in the form of carbonate of lime: that is, as marble, limestone, and chalk—these all being of the same composition. In manufacturing caustic (or quick) lime, it is customary to burn the carbonate of lime in a kiln; by this means the carbonic acid is thrown off into the atmosphere and the lime remains in a pure or caustic state. A French chemist states that every cubic yard of limestone that is burned, throws off ten thousand cubic yards of carbonic acid, which may be used by plants. This reminds us of the story of Sinbad the sailor, where we read of the immense genie who came out of a very small box by the sea-shore, much to the surprise of Sinbad, who could not believe his eyes, until the genie changed himself into a cloud of smoke and went into the box again. Sinbad fastened the lid, and the genie must have remained there until the box was destroyed.
Now man is very much like Sinbad, he lets the carbonic acid out from the limestone (when it expands and becomes a gas); and then he raises a crop, the leaves of which drink it in and pack the carbon away in a very small compass as vegetable matter. Here it must remain until the plant is destroyed, when it becomes carbonic acid again, and occupies just as much space as ever.
The burning of limestone is a very prolific source of carbonic acid.
MAGNESIA
What do you know about magnesia?
What is phosphoric acid composed of?
With what substance does it form its most important compound?
Magnesia is the remaining alkali of vegetable ashes. It is well known as a medicine, both in the form of calcined magnesia, and, when mixed with sulphuric acid, as epsom salts.
Magnesia is necessary to nearly all plants, but too much of it is poisonous, and it should be used with much care, as many soils already contain a sufficient quantity. It is often found in limestone rocks (that class called dolomites), and the injurious effects of some kinds of lime, as well as the barrenness of soils made from dolomites, may be attributed entirely to the fact that they contain too much magnesia.
ACIDS
PHOSPHORIC ACID
Phosphoric acid.—This subject is one of the greatest interest to the farmer. Phosphoric acid is composed of phosphorus and oxygen. The end of a loco-foco match contains phosphorus, and when it is lighted it unites with the oxygen of the atmosphere and forms phosphoric acid; this constitutes the white smoke which is seen for a moment before the sulphur commences burning. Being an acid, this substance has the power of combining with any of the alkalies. Its most important compound is with lime.
Will soils, deficient in phosphate of lime, produce good crops?
From what source do plants obtain their phosphorus?
Phosphate of lime forms about 65 per cent. of the dry weight of the bones of all animals, and it is all derived from the soil through the medium of plants. As plants are intended as food for animals, nature has provided that they shall not attain their perfection without taking up a supply of phosphate of lime as well as of the other earthy matters; consequently, there are many soils which will not produce good crops, simply because they are deficient in phosphate of lime. It is one of the most important ingredients of manures, and its value is dependent on certain conditions which will be hereafter explained.
Another use of phosphoric acid in the plant is to supply it with a small amount of phosphorus, which seems to be required in the formation of the seed.
SULPHURIC ACID
What is sulphuric acid composed of?
What is plaster?
What is silica?
Why is it necessary to the growth of plants?
What compounds does it form with alkalies?
Sulphuric acid is important to vegetation and is often needed to render soils fertile. It is composed of sulphur and oxygen, and is made for manufacturing purposes, by burning sulphur. With lime it forms sulphate of lime, which is gypsum or 'plaster.' In this form it is often found in nature, and is generally used in agriculture. Other important methods for supplying sulphuric acid will be described hereafter. It gives to the plant a small portion of sulphur, which is necessary to the formation of some of its parts.
NEUTRALS
SILICA
How can you prove its existence in corn stalks?
What instance does Liebig give to show its existence in grass?
How do we supply silicates?
Why does grain lodge?
What is the most important compound of chlorine?
This is sand, the base of flint. It is necessary for the growth of all plants, as it gives them much of their strength. In connection with an alkali it constitutes the hard shining surface of corn stalks, straw, etc. Silica unites with the alkalies and forms compounds, such as silicate of potash, silicate of soda, etc., which are soluble in water, and therefore available to plants. If we roughen a corn stalk with sand-paper we may sharpen a knife upon it. This is owing to the hard particles of silica which it contains. Window glass is silicate of potash, rendered insoluble by additions of arsenic and litharge.
Liebig tells us that some persons discovered, between Manheim and Heidelberg in Germany, a mass of melted glass where a hay-stack had been struck by lightning. They supposed it to be a meteor, but chemical analysis showed that it was only the compound of silica and potash which served to strengthen the grass.
There is always enough silica in the soil, but it is often necessary to add an alkali to render it available. When grain, etc., lodge or fall down from their own weight, it is altogether probable that they are unable to obtain from the soil a sufficient supply of the soluble silicates, and some form of alkali should be added to the soil to unite with the sand and render it soluble.
CHLORINE
Of what use is chloride of lime?
What is oxide of iron?
What is the difference between the peroxide and the protoxide of iron?
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,6 we are enabled to classify them in a simple manner, so that they may be recollected. They are as follows:—
CHAPTER V
GROWTH
Of what does a perfect young plant consist?
How must the food of plants be supplied?
Can carbon and earthy matter be taken up at separate stages of growth, or must they both be supplied at once?
Having examined the materials of which plants are made, it becomes necessary to discover how they are put together in the process of growth. Let us therefore suppose a young wheat-plant for instance to be in condition to commence independent growth.
It consists of roots which are located in the soil; leaves which are spread in the air, and a stem which connects the roots and leaves. This stem contains sap vessels (or tubes) which extend from the ends of the roots to the surfaces of the leaves, thus affording a passage for the sap, and consequently allowing the matters taken up to be distributed throughout the plant.
What seems to be nature's law with regard to this?
What is the similarity between making a cart and raising a crop?
In the growth of a young plant, what operations take place about the same time?
It is necessary that the materials of which plants are made should be supplied in certain proportions, and at the same time. For instance, carbon could not be taken up in large quantities by the leaves, unless the roots, at the same time, were receiving from the soil those mineral matters which are necessary to growth. On the other hand, no considerable amount of earthy matter could be appropriated by the roots unless the leaves were obtaining carbon from the air. This same rule holds true with regard to all of the constituents required; Nature seeming to have made it a law that if one of the important ingredients of the plant is absent, the others, though they may be present in sufficient quantities, cannot be used. Thus, if the soil is deficient in potash, and still has sufficient quantities of all of the other ingredients, the plant cannot take up these ingredients, because potash is necessary to its life.
If a farmer wishes to make a cart he prepares his wood and iron, gets them all in the proper condition, and then can very readily put them together. But if he has all of the wood necessary and no iron, he cannot make his cart, because bolts, nails and screws are required, and their place cannot be supplied by boards. This serves to illustrate the fact that in raising plants we must give them every thing that they require, or they will not grow at all.
In the case of our young plant the following operations are going on at about the same time.
The leaves are absorbing carbonic acid from the atmosphere, and the roots are drinking in water from the soil.
What becomes of the carbonic acid?
How is the sap disposed of?
What does it contain?
How does the plant obtain its carbon?
Its oxygen and hydrogen?
Its nitrogen?
Its inorganic matter?
Under the influence of daylight, the carbonic acid is decomposed; its oxygen returned to the atmosphere, and its carbon retained in the plant.
The water taken in by the roots circulates through the sap vessels of the plant, and, from various causes, is drawn up towards the leaves where it is evaporated. This water contains the nitrogen and the inorganic matter required by the plant and some carbonic acid, while the water itself consists of hydrogen and oxygen.
Thus we see that the plant obtains its food in the following manner:—
What changes does the food taken up by the plant undergo?
Many of the chemical changes which take place in the interior of the plant are well understood, but they require too much knowledge of chemistry to be easily comprehended by the young learner, and it is not absolutely essential that they should be understood by the scholar who is merely learning the elements of the science.
It is sufficient to say that the food taken up by the plant undergoes such changes as are required for its growth; as in animals, where the food taken into the stomach, is digested, and formed into bone, muscle, fat, hair, etc., so in the plant the nutritive portions of the sap are resolved into wood, bark, grain, or some other necessary part.
The results of these changes are of the greatest importance in agriculture, and no person can call himself a practical farmer who does not thoroughly understand them.