A lecture on ‘‘ Agricultural Chemistry ” was given last Friday night, in the Cambridge School, by the master, Mr. H. CapeWilliamson. There was a fair attendance, and the lecture was listened to with marked attention throughout. Mr. Megson, who was in the chair, briefly stated that the proceeds were in aid of a fund to purchase a harmonium for school use, to become school property. He then introduced the lecturer, Mr. Williamson, who stated that by the term “ Agricultural Chemistry ” was not meant chemistry or geology, but scientific agriculture. A knowledge of this subject could be practically applied to the daily occupations of their lives, more particularly with farmers, and it had, therefore, an actual money value. To raise larger crops from their land they must have an increased knowledge of the culture of the soil, and if the farmer aspires pecuniarily to something more than mere living and paying expenses, a knowledge of the subject was absolutely necessary fco the practical man, for the whole work of the farmer was simply to raise the largest crops, at the smallest cost, and with the least injury to the soil ; and to enable him to do this he must know the nature and composition of his crops, land, and the manures which he applies or ought to apply f o his land. The chemistry of his crops was a matter of groat importance, because he could not restrict his operations to such crops as the land was particularly adapted for, but must endeavor to render his laud capable of carrying more or less the crops most required for daily consumption. Plants consisted of two classes of constituents or parts—an inorganic, which might be called the foundation, and the organic, which could be considered as the superstructure. Plants contain usually much organic matter, derived partly from the air and partly from the soil. The organic part of plants chiefly consisted of woody fibre, starch, sugar, gum, albumen, gluten, oil, or fat; and these consisted of four elementary bodies —carbon, hydrogen, oxygen, and nitrogen, with small quantities of sulphur and phosphorous. Of these, starch, sugar, gum, oils, fats, and woody fibre, contained only the first three ; the gluten of wheat, fibrin of flesh, white of egg, gelatine, contain all six. Plants required for a healthy growth, supplies of food obtained partly from the air (organic food) by their leaves, and partly from the soil (inorganic) in the form of carbonic acid gas, retaining only the carbon, and giving off the oxygen to the air again.- They also absorbed watery vapor from the air, which served to moisten the leaves and stems, to fill their cells, and to produce the substance of the plant itself. Plants also take in carbon from the soil in the forrii of carbonic and humic acids, and by the aid of this carbon they secreted vascular tissue, starch, sugar, and other carbonaceous principles. The nitrogen the plants required was absorbed in the form of ammonia and nitric acid, of which it is a constituent. By its aid the plant secreted gluten, albumen, and other nitrogenous principles. Water was necessary to plant life, and it had three important properties —first, that of dissolving solid and other substances in the soil, enabling it to take up and convey into the roots and stems of planes the various kinds of food required ; second, the property of rising in vapor and falling again as dew ; and, third, the property of yielding oxygen and hydrogen, to enable the growing plant more easily and quickly to form the various compound substances of which the parts consist. The inorganic or mineral part of the soil consisted of soda, potash,f magnesia, lime, silica, oxide of manganese, oxide of iron, alumina, sulphuric, phosphoric, and boracic acids; chlorine, iodine, bromine, and fluorine. The organic part of the soil was obtained from the roots and stems of decayed plants, from the dung and remains of animals and insects of various kinds. It does not usually form a large proportion of the soil, except in the case of a peaty soil. The inorganic part was obtained from the crumbling down of rocks and stones which consist principally of more or less hardened sandstones, limestones, and clays, either alone or mixed together in various proportions. Air. Williamson hero referred at some length to the improvement of the soil by ploughing, subsoiling, and drainage, and then went on to say that the mineral or inorganic part of the soil had three purposes to serve—first, as a medium for the plants to root or fix themselves in to keep an upright position ; second, to supply inorganic food ; and, third, to prepare the crude constituents of manure into available plant food. The mineral part of soil consisted chiefly of sand, clay, and lime, and about eight or nine other substances, such as soda, potash, magnesia, etc., and a soil to be fertile must contain all these, because plants require them all for their healthy growth, though not in equal proportions ; and if a soil was deficient in any one of them, good crops would not grow on it. In fertile soils all these inorganic substances were present, and in proper proportions. In barren soils some of them are, or may bo, wholly wanting. A soil might be barren if it contained a very large proportion of some such readily soluble matter as common salt, which is in great quanties injurious to the soil ; or some matter like green vitriol which is injurious in small quantities. Lime was often applied to such a soil as this because it converted the green vitriol into sulphate of lime, a substance beneficial to vegetation. The mineral substances which the grain of the crops draws more especially from the soil were phosphoric acid, potash, and magnesia. The roots of potatoes, and turnips chiefly exhausted it of the first two, so that by injudicious treatment a fertile soil could be rendered barren ; for if the same kind of cropping were carried on year after year without a supply of proper manure, the land would gradually become less and less productive ; because all crops draw certain substances from the soil, which, after a few years, the soil would be unable to furnish in sufficient quantities to the growing crop. This, of course, could be obviated by returning to the land as much, or more, of the substances the crops had taken out. Unless done the land could not be kept in proper condition. This a farmer could afford to do, for he laid on the land what was almost a worthless refuse, which would be converted into valuable produce. There are three principal kinds of manure or plant foods—vegetable, animal, and mineral. Vegetable manures are the parts usually buried in the soil to enrich it—such as grass, clover, straw, turnip tops, etc. Animal manures are the blood, flesh, bones, hair, and wool of animals, and and the bodies and refuse of fish. Bones are crushed in mills, and sifted into different sizes and applied to the land. Fifty years ago when it was proposed to use them in Wigtonshire as a manure, the objection urged was “ They’ll do naething but breed maggots to eat everything off the land. ” Bones consist of gelatine or glue, and bone earth, both good manures. Of the droppings or dung of animals, that of birds, or guano, was the most valuable, on account of the ammonia contained in it. Horse dung was more valuable than cow’s, because the large quantity of urine voided by the cow as compared with the horse carried off a great proportion of substances which would cause it to ferment. The dung of animals differed from the food on which they live, in containing a less quantity of carbon and a greater quantity 'of nitrogenous and saline matter. The carbon was less because it had been to a great extent thrown off by the lungs, and this large proportion of nitrogen and saline matters was one cause of the greater activity of
the manure. The nitrogen assumes for the most part the form of ammonia, which, dissolved in the soil, enters the roots of plants. Of the mineral manures, the most important were phosphate of lime, nitrate of soda, sulphates 6f lime, soda, magnesia, and ammonia, salt, gypsum, soot, and lime. The different properties of these were fully described by Mr. Yviiliamson, Several questions were asked by members of the audience, which were replied to by Mr. Williamson. A vote of thanks was, accorded by acclamation to the lecturer, and themeeting terminated with a vote of thanks to the Chairman.
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