The Temuka Leader TUESDAY, FEBRUARY 11, 1884. WHAT FARMERS OUGHT TO KNOW. AGRICULTURAL CHEMISTRY.

Temuka Leader, Issue 1138, 12 February 1884, Page 2

The Temuka Leader TUESDAY, FEBRUARY 11, 1884. WHAT FARMERS OUGHT TO KNOW. AGRICULTURAL CHEMISTRY.

11. We now pass on to consider a most important element, Nitrogen. We saw before that four-fifths of the atmosphere was composed of this gas. It is an inert, invisible, inodouous, tasteless, colorless element. In its uncombined form it is remarkable fox its wonderful laziness, inertness and inactivity ; in its combined state it is equally remarkable for activity and strongly marked properties. The chief objects of the gas in the air seem to be: to dilate the otherwise too active oxygen, and afford a ready source for absorption by plants. The active oxygen were it not weakened by dilution by nitrogen would seize r.n everything, on account of its irresistible tendency to combine with other elements, and as ve have seen it would thus effect wholesale combustion. It does not support life. In its elementary state it exhibits few striking qualities, but when in combination it produces such substances as ammonia, nitric acid, chloride of nitrogen, gun-cotton, nitro-glycenne, all of which exhibit strong and characteristic properties'. Nitrogen is the characteristic clement of a large body of substances called nitrogenous, such are hoofs, hair, hides, feathers, flesh. It forms a large part of the flesh, and thus we find it as a necessary nourishing principle in all edible grains and fruits. Ammonia is composed of nitrogen and hydrogen, and when speaking of ammonia as a valuable portion of manures we must recollect that it is due to the fact of its containing a large proportion of nitrogen, which is so necessary in building up the flesh of animals; the same remark applies to nitric acid, and to other substances wo shall meet with further on. The next constituent of the atmosphere that calls for remark is Carbonic Acid. Carbonic acid is composed of carbon and oxygen. Carbonic acid is wrongly so called, and only popularly carbonic anhydride, or the binoxide of carbon, would be more correct names for it. However, we shall abide by the popular appellation. It is an invisible gas possessing but a slight odour, it is heavier than air and is a poison. But for the law of the “diffusion of gases” we would have a layer of this poisonous gas constantly collecting and remaining on the ground, and soon we would all perish. But nature has provided means by which its equal distribution ia accomplished. The two gases (oxygen and nitrogen) we have just been considering are elementary bodies—bodies that cannot be further split up by any means Carbonic acid, however, is a compound substance, ' being composed of the solid carbon, or charcoal, or lampblack, or soot, or graphite, and the gas oxygen in chemical combination. It is from carbonic acid gas that plants obtain a greet portion of their food ; this they do in two ways : tha one by absorbing it from the air, and the other by taking it up dissolved in water. This gas is thus a most important one in considering the growth of plants. Carbonic acid exists in a fixed state in many miner il.--. The term fixed is applied to volatile substances such as ammonia and carbonic acid when they have combined chemically with other substances, and exist in union with them in a fixed state ; that is, not able to fly away or volatilise. Tims limestone is known as carbonate of calcium, the carbonate is built up from the oxide. The metal cah iun combines with the gas oxygen to form an oxide called oxide of calcium, or as it is more commonly termed, lime; oxide of calcium is able to combine with carbonic acid, and produces eaibonato of calcinm. In this state the volatile gas is fixed, for I it remains in chemical combination with

the lime. The process of “ burning ”or “firing ’’limestone is a process of unfafaj the carbonic acid. Heat is ab’e t) volatilise the gas, and when the g*s go js off it leaves, as we have seen, 1 mo, or oxide of calcium. Now it is rpp* ent that the common expression—“ turn ug ” limestone-—is quite incorrect. Wj saw before that burning or combustion was the result of a union between oxygen and other substances ; in firing lime, however, what takes place is the escape of a gas, carbonic acid, so that the two processes are entirely distinct, and it is quite erroneous to speak of them by the same name. A simple experiment will show how we can produce limestone from lime. Thoroughly dissolve a small quantity of lime in water. Take a glass tube, insert it into the water end blow through it with the breath, and in a short time a milky white substance will appear in the water ; if the water is allowed to stand for a while the deposit will subside to the bottom of |the glass. Now this white material is limestone. We had lime (oxide of calcium) dissolved in the water, through it we passed carbonic acid, for we have already noticed that one of the chief constituents of the breath is this gas ; the gas united with the lime to form carbonate of calcium or limestone, which beiug insoluble in water, was precipitated as a milky white material. Now this process is the converse of that of firing lime, in the one we effect the union of carbonic acid gas with lime, in the other we effect their separation by employing heat. In the above experiment, if breathing through the water be continued for some time after the appearance of the limestone it will bo followed by its disappearance. This is due to the fact that limestone though not soluble in pure water is soluble in water charged with carbonic acid. All the carbonic acid necessary for converting the lime to limestone having been obtained, further breathing charges the water with the gas, and thus the white again disappears owing to its solubility in water charged with carbonic acid.

A remarkable property of this gas is its power of effervescing. When any acid is thrown on limestone effervescence takes place, this is due to the escape of the acid gas. What constitutes the briskness in bottled beer, in champagne, in lemonade, in spring water is the pressure of carbonic acid.

The gas, as wo have seen is volatile, and may be expelled from its compounds by the application of heat. Its composition must be carefully remembered, an element carbon and the gas oxygen. It is produced in the lungs, and exhaled. Many kinds of food owe their utility to the presence of carbon in them in such a state that it ray be furnished to the lungs, there to unite with oxygen and become carbonic acid. Before we can fully appreciate the part that the gas plays in building up the organisms of plants and animals, the knowledge of soma facts respecting carbon itself, is necessary. Carbon. Carbon is an elementary solid substance. In every 22lbs of carbonic acid gas there are six of carbon, or charcoal. Charcoal, soot, lampblack, graphite, coal, all consist essentially of carbon in different degrees of purity. Charcoal and coke are tolerably pure carbon; coal is carbon mixed with a variety of earthy and other matters, and is thus very impure. Graphite, soot and lampblack are also impure carbon, and the diamond almost perfectly pure. The wonderful distinction that exists between the substances just enumerated and the diamond ia, that in the first cases the carbon is uncrj'stnlline and in the latter it is crystalline ; thus materials apparently differing so much, are by chemistry proved to be composed of one and the same element. Carbon is a very abundant substance. It forms a very large proportion of the weight of animals and plants ; about half the weight of dry wheat, hay, roots, etc., consists of carbon. . . . . When wood or vegetable products are burned their carbon, and other combustible substances they contain, are consumed ; that is, the carbon combines with the oxygen of the air and passes off as carbonic acid. If, however, the combustion is arrested before all the inflammable matter is burne 1 away the greater part of the carbon is obtained in the form of charcoal. Charcoal, or carbon, in the black, brittle condition usually met with, is distinguished for its insoluble and imperishable qualities. A piece of charcoal buried in the earth will remain there any length of time without showing symptoms of decay. Advantage is often taken of this property of charcoal to preserve from decay timber that is buried in the earth, as gate posts, posts of fences etc. By charring the surface of wood n layer of carbon is formed which in a great measure preserves the enclosed wood from further destruction. Another remarkable property of charcoal is its extreme porosity. On examining a piece of charcoal by a magnifying glass it will be found to be full of minute pores or tubes ; these fine tubes absorb gases, in tha same manner as a sponge does fluids. In this way charcoal is capable of absorbing and fixing largo quantities of certain gases. Its power of absorbing ammonia gas is particularly large. In a dry condition charcoal absorbs 700 times its own volume of this gas ” This property of charcoal is to be carefully noticed. It is owing to its power of absorbing gases that it is useful in removiug the offensive and contagious effluvia of hospitals and sick rooms, as well as for purifying water—as in our charcoal filters. Now a portion of the soil, especially garden mould, consists of a substance called humus, and this humus is carbon or charcoal which has resulted from the decaying of vegetable matter in the soil , and as we have stated that charcoal has a property of absorbing gases, humus is capable of absorbing ammonia, which ia very volatile. This property of ciiarcoal plays a very important part, for ammonia, as we shall see further on, is an essential constituent in the food of plants. We nr» now in a position to understand the wonderful cycle of changes that take place in the vegetable and animal world. We will suppose an animal eats a olant. Vegetable life, as has been stated, is composed to a great extent of the elementary substance, carbon. Now this is taken into the body of the animal when the plant is eaten. Now we have seen what becomes of it there. In the lungs the carbon unites with oxygen of the atmosphere and forms carbonic acid gas, and in this shape it is exhaled. Now we see that carbonic acid gas is produced on the face of the globe in immense quantities. But we learn that it is a poisonous gas, and the question arises, .

What must become of it ? Carbonic acid is composed of carbon and oxygen, and we have seen that plants need carbon ; now plants have tho power of splitting this gas up, appropriating the carbon for themselves and expelling the oxygen, and we have seen that man and the animals are constantly inhaling oxygen. The c irben of the plant is again eaten by the animal, and union with oxygon again effected, and so on. Thus we have an unceasing round : animal life constantly forming carbonic acid, plant life constantly splitting it up, appropriating what it wants and rejecting what it doss not want. But it may be asked, What is the object of all this t vVe have before seen that when two substances combine chemically, heat it always liberated, and one of the great objects of these continual transformations is the production of heat in the body of animals by the oxygen of the air going into chemical combination with the carbon. • Another substance still remains to be glanced at before entering on a brief consideration of soils— Ammonia.

Ammonia, that volatile liquid, is composed of nitrogen (a gas we have already noticed) and another lestk important one in agricultural chemistry, called hydrogen. The importance of ammonia is due to its being a source of nitrogen to plants, and thus is an essential in manures. It has a pungent odour, is constantly volatilising, is invisible as a gas, and a very nouiishing material for plants. Ammonia exists in small quantities in the air, it is got from the most nitrogenous parts of animals, as horns, hoofs, etc., it is also being constantly liberated from farmyard manure.

i mmonia is volatile ; that ie, it has a tendency to evaporate and escape as a gas. To “ fix ” ammonia is to get it into combination with some substance so that the product thus formed will not be volatile. Now ammonia is a very strong alkali , by which is meant a body possessed ot qualities opposed to those of an acid, such as soda and potash. Now when an acid and alkali meet they neutralise each other and produce a compound called a salt, possessed of qualities neither those of au alkali nor yet of an acid.

“ Ammonia in a free state is often liberated in stables or from recentlyturned farm yard manure. In this condition it rapidly flies off, and is wasted, unless measures be taken to prevent it. This is best done by sprinkling the manure with diluted oil of vitriol (sulphuric acid), or in stables by diluting it with water, and adding sawdust ; exposing it in basins or other shallow vessels. The ammonia is thus converted into a salt and is fixed.”

The chief means the plant has for obtaining ammonia are the following : (1). It has the power to a very small degree of absorbing it. (2). When electricdischarges,during thunderstorms, take place, a chemical union often happens. This chemical union is between the gases hydrogen, oxygen and nitrogen, all present in the atmosphere ; this produces the strong corrosive substance, nitric acid. The acid and the alkaline ammonia meeting, a union takes place, and as we have seen a salt is produced. This salt is nitrate of ammonia. It is carried down I by the rain and deposited in the soil from which the plant obtains it. (3). We have noticed a substance humus, which has the / power of absorbing ammonia ; this is continually storing up the gas and supplying it to the plant, and then re-absorbing more from the atmosphere. (4.) Animal matters in the soil are constantly decaying and affording the gas directly. (5). In cases where plants cannot obtain it, it has to bo supplied by manures Farm yard manure, soot, guano, all contam essentially ammonia, which it must be remembered is the great source of nitrogen to plant life, (To he Continued.)