ELEMENTS
OF
AGRICULTURAL CHEMISTRY, &c.
CHAPTER I.
Distinction between Organic and Inorganic Substances.—The Ash of Plants.—Constitution of the Organic Parts of Plants.—Preparation and Properties of Carbon, Hydrogen, and Nitrogen.—Meaning of Chemical Combination.
The object of the practical farmer is to raise from a given extent of land the largest quantity of the most valuable produce at the least cost, and with the least permanent injury to the soil. The sciences either of chemistry or geology throw light on every step he takes or ought to take, in order to effect this main object.
SECTION I.—OF THE VEGETABLE AND EARTHY
OR THE ORGANIC AND INORGANIC
PARTS OF PLANTS.
In the prosecution of his art, two distinct classes of substances engage his attention—the living crops he raises, and the dead earth from which they are gathered. If he examine any fragment of an animal or vegetable, either living or dead, he will observe that it exhibits pores of various kinds arranged in a certain order—that it has a species of internal structure—that it has various parts or organs—in short, that it is what physiologists term organized. If he examine, in like manner, a lump of earth or rock, he will perceive no such structure. To mark this distinction, the parts of animals and vegetables, either living or dead—whether entire or in a state of decay, are called organic bodies, while earthy and stony substances are called inorganic bodies.
Organic substances are also more or less readily burned and dissipated by heat in the open air; inorganic substances are generally fixed and permanent in the fire.
But the crops which grow upon it, and the soil in which they are rooted, contain a portion of both of these classes of substances. In all fertile soils, there exists from 3 to 10 per cent. of vegetable or other matter of organic origin; while, on the other hand, all vegetables, as they are collected for food, leave, when burned, from one-half to twenty per cent. of inorganic ash.
If we heat a portion of soil to redness in the open air, the organic matter will burn away, and, in general, the soil, if previously dry, will not be materially diminished in bulk. But if a handful of wheat, or of wheat straw, or of hay, be burned in the same manner, the proportion that disappears is so great, that in most cases a comparatively minute quantity only remains behind. Every one is familiar with this fact who has seen the small bulk of ash that is left when weeds, or thorns, or trees, are burned in the field, or when a hay or corn-stack is accidentally consumed. Yet the ash thus left is a very appreciable quantity, and the study of its true nature throws much light, as we shall hereafter see, on the practical management of the land on which any given crop is to be made to grow.