The Elements of Agriculture A Book for Young Farmers, with Questions Prepared for the Use of Schools, George E. Waring [read aloud books TXT] 📗

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.

SECTION 1 (THE PLANT) CHAPTER IV (INORGANIC MATTER) Pg 24

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.

SECTION 1 (THE PLANT) CHAPTER IV (INORGANIC MATTER) Pg 25

 

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.

SECTION 1 (THE PLANT) CHAPTER IV (INORGANIC MATTER) Pg 26

 

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.

SECTION 1 (THE PLANT) CHAPTER IV (INORGANIC MATTER) Pg 27

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.

SECTION 1 (THE PLANT) CHAPTER IV (INORGANIC MATTER) Pg 28

 

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.

FOOTNOTES Pg 29

[B] Bromine, iodine, etc., are sometimes detected in particular plants, but need not occupy the attention of the farmer.

[C] This classification is not strictly scientific, but it is one which the learner will find it well to adopt. These bodies are called neutrals because they have no