Carbonization

“ It is an extremely familiar material on the earth; for instance, coal is chiefly composed of carbon. Charcoal when burned leaves only a few ashes. All the substance that has vanished during combustion is carbon; in fact, it is not too much to say that carbon is found abundantly not only in wood, but in almost every form of vegetable matter. The food we eat contains abundant carbon, and it is an important constituent in the building up of our own bodies. Generally speaking, carbon is not found in a pure state—it is associated with other substances. ”

“ Thus in coal and jet the carbon is of stable character, such as we might expect to result from the slow decomposition of vegetable matter, and the products of this action are not volatile or liable to be suddenly dissociated or broken up. On the other hand, when we deal with the hydrocarbons as they are called, in the shape of rock gas, naphtha, petroleum, tar, asphaltum, and similar substances, we see how the carbon has become subordinated to the hydrogen part of the compounds, with the result of rendering them more or less unstable in their character. ”

“ It is not acted on at ordinary temperatures by most reagents, but at a higher temperature it combines directly with many of the elements, forming compounds called carbides. When heated in the presence of sufficient oxygen it burns, forming carbon dioxide.
Uses of carbon. The chief use of amorphous carbon is for fuel to furnish heat and power for all the uses of civilization. An enormous quantity of carbon in the form of the purer coals, coke, and charcoal is used as a reducing agent in the manufacture of the various metals, especially in the metallurgy of iron. ”

“ When we burn coal, which is a vegetable product, we find that the carbon and hydrogen escape as carbonic acid and water, accompanied by nitrogen, sulphuric acid, and volatile hydrocarbons. The residue consists mainly of silica and alumina, which are removed from the furnace in the form of clinker and ash. The water ultimately returns to the earth in the form of rain or dew; the carbonic acid is ultimately absorbed by green plants, and, by stimulating the growth of these, helps to furnish us with more combustible material; while the residue is almost a waste product. ”

“ Only one-fourth of the earth's surface is land, and perhaps only one-fourth of this land is cropped, and the average crop is about one-fourth of three tons; so that the total present supply of carbon in the air would be sufficient for about two hundred and fifty years. But as a matter of fact the supply is permanently maintained by the carbon cycle. Thus the carbon of coal that is burned in the stove returns to the air in carbon dioxid; and all combustion of coal and wood, grass and weeds, and all other vegetable matter returns carbon to the atmosphere. ”

“ The carbonic acid gas produced simply by the breathing of the great human family amounts every year to about 160,000,000,000 cubic meters, which represents 86,270,000,000 kilograms of burnt carbon. Piled up, this carbon would form a mountain one league round at its base and between four hundred and five hundred meters high. So much carbon is required by man to maintain his natural heat. All of us together eat this mountain of carbon in our food and in the course of the year dissipate it all in the air, a breathful at a time ”

“ The volatile gases burn more readily than the carbon, and are the first substances to be driven off, so that the carbon is left behind nearly pure. In the same way we have driven off all the gases from the half-burned match and left the carbon. The teacher should have a piece of charcoal to show the pupils. It still retains all the markings of the wood.
If the combustion is continued, the carbon also unites with the oxygen of the air, till it is all converted into carbonic acid gas. ”

“ These blocks having been allowed to dry and harden, are subsequently carbonized by being subjected to a process of incineration by heat; and, in this manner, all the combustible ingredients are burnt out of the block, leaving nothing behind but the animal charcoal in the form of a block of charcoal, permeated throughout by innumerable pores, admirably adapted for the mechanical infiltration of fluids, while subjecting them, in a minutely subdivided state, to the chemical absorptive and purifying action of the carbon itself. ”

“ Carbon dioxide, which is formed by the complete oxidation of carbon, is a gas with a sweetish odour and taste, having a strong affinity for alkalies, and forming a series of compounds termed carbonates. The gas itself occurs in nature, and is sometimes met with in quantity in mining. The carbonates occur largely in nature, forming mountain masses of limestone, &c. Carbonates of many of the metals, such as carbonate of lead (cerussite) , carbonate of iron (chalybite) , carbonates of copper (malachite and chessylite) , and carbonate of magnesia (magnesite) , are common. ”

“ It has often been suggested that, during the Carboniferous period, the atmosphere must have been warmer and more charged with aqueous vapour and carbon dioxide than at the present day, to admit of so luxuriant a flora as that from which the coal-seams were formed. There seems, however, to be at present no method of arriving at any certainty on this subject. Lastly, the amount of carbonic acid absorbed in the weathering of rocks at the surface, and the consequent production of carbonates, represents an enormous abstraction of this gas. ”

“ I said that there was carbon or charcoal in all common lights, so there is in every common kind of fuel. If you heat coal or wood away from the air, some gas comes away, and leaves behind coke from coal, and charcoal from wood; both carbon, though not pure. Heat carbon as much as you will in a close vessel, and it does not change in the least; but let the air get to it, and then it burns and flies off in carbonic acid gas. This makes carbon so convenient for fuel. But it is ornamental as well as useful, uncle. The diamond is nothing else than carbon. ”

“ When the intensity of the heat has reached a certain degree, a part of the carbon unites with part of the oxigen and produces carbonic acid, which by means of caloric is melted into the gazeous state and forms carbonic acid gas; at the same time, part of the hidrogen of the coal combines with another portion of carbon and caloric, and forms the carburetted hidrogen gas, which varies considerably in its constitution, according to the circumstances under which it is produced; a portion of olifiant gas, carbonic oxid, hidrogen, and sulphuretted hidrogen, is also produced during the process. ”

“ It has been said that these gases are simply locked up in the interstices of the carbonaceous matter and are liberated in its excavation; but all who have worked coal mines know that such accumulations are not sufficient to supply the enormous and continuous flow which comes from all parts of the mass penetrated. We have ample proof, moreover, that coal, when exposed to the air, undergoes a kind of distillation, in which the evolution of carbonic acid and hydrocarbon gases is a necessary and prominent feature. ”

“ Plants when decomposing on the surface of the ground give off their carbon to the atmosphere in the shape of carbon dioxid gas leaving only the strictly inorganic or mineral matter behind. When, however, they are protected from the oxidizing influence of the air, by water or by other plant growth, decomposition is greatly retarded, and a large portion of the carbonaceous and volatile matters is retained, and by this means together with pressure from the overlying mass, the material becomes slowly converted into coal. ”

“ We may, indeed, fairly estimate the amount, if we ascertain the quantity of wood and coal consumed, of all the carbon which combines with oxygen while burning, and escapes into the air, either as carbonic acid or carbonic oxide. The former gas, the same as that which accumulates in deep wells and in brewers’ vats, is highly destructive to life, producing very distressing symptoms, even when mixed with atmospheric air, in but slight excess over that proportion which it commonly contains. ”

“ It naturally follows that if along with the requisite temperature sufficient pressure is applied, liquefaction of carbon will take place, when on cooling it will crystallise. But carbon at high temperatures is a most energetic chemical agent, and if it can get hold of oxygen from the atmosphere or any compound containing it, it will oxidise and fly off in the form of carbonic acid. Heat and pressure therefore are of no avail unless the carbon can be kept inert. ”

“ Not only is carbon concealed in sugar, but it is present in all plant and animal matter. That is why burning almost any kind of food makes it black. You drive off most of the other elements and separate the food into its parts by getting it too hot; the water evaporates [pg 301] and so does the nitrogen; what is left is mainly black carbon.
Making hydrogen come out of hiding. The light gas, hydrogen, conceals itself as perfectly as carbon does by combining with other elements. It is hiding in everything that is sour and in many things that are not sour. ”

“ The reduction of the fuel to carbon dioxide and water produces every heat unit available since the latter compounds represent the lowest state to which the fuel can be burned. Carbon however may be burned to an intermediate state without the production of its entire calorific contents when there is not sufficient oxygen present to thoroughly consume the fuel. Incompletely consumed carbon produces a gas, carbon monoxide, as a product of 15combustion, and a quantity of solid carbon in a finely subdivided state known as “soot.” ”

“ It is so; and when all the hydrogen is consumed, the carbon continues to burn without flame. But again, as I mentioned when speaking of the gas-lights, the hydrogen gas produced by the burning of coals is not pure; for, during the combustion, particles of carbon are successively volatilized with the hydrogen, with which they form what is called a hydro-carbonat, which is the principal product of this combustion.
Carbon is a very bad conductor of heat; for 304 this reason, it is employed (in conjunction with other ingredients) for coating furnaces and other chemical apparatus. ”

“ The carbon of our fuel produces, in burning, carbonic acid, but carbon is not the only substance in ordinary fuel. Most coals contain sulphur, and in burning, this body produces sulphurous acid, also a gas, which is highly irritating and poisonous, particularly to plants, and which, mixing with the air, renders the city as injurious to the organization of a plant as the carbonic acid to the respiration of an animal. ”

“ Carbonic acid—the gas resulting from the complete combustion of carbon—should be entirely removed by the lime purifiers, as the presence of even a small percentage detracts materially from the illuminating power. ”

“ Fig. 374.—Experiment showing that carbonic acid contains oxygen and carbon.
The compounds of carbon with hydrogen are important. There is the “light” carburetted hydrogen (CH4) , which is usually known as fire-damp in coal mines. It is highly inflammable and dangerous. The safety-lamp invented by Davy is a great protection against it, for as the gas enters it is cooled by the wire, and burns within harmlessly. The explosion warns the miner. “Heavy” carburetted hydrogen possesses double the quantity of carbon (C2H4) . It is also explosive when mixed with oxygen. ”

“ Now let us try to make some carbonic acid.—Will you, Emily, decant some oxygen gas from this large jar into the receiver in which we are to 293 burn the carbon; and I shall introduce this small piece of charcoal, with a little lighted tinder, which will be necessary to give the first impulse to the combustion.
EMILY.
I cannot conceive how so small a piece of tinder, and that but just lighted, can raise the temperature of the carbon sufficiently to set fire to it; for it can produce scarcely any sensible heat, and it hardly touches the carbon. ”

“ A man in twenty-four hours converts as much as seven ounces of carbon into carbonic acid; a milch cow will convert seventy ounces, and a horse seventy-nine ounces, solely by the act of respiration. That is, the horse in twenty-four hours burns seventy-nine ounces of charcoal, or carbon, in his organs of respiration, to supply his natural warmth in that time. All the warm-blooded animals get their warmth in this way, by the conversion of carbon, not in a free state, but in a state of combination. ”

“ From these we may well conclude that enormous variations have occurred, but not that the variation has always proceeded in the same direction.
“Carbonic acid is supplied to the atmosphere by the following processes:— (1) volcanic exhalations, and geological phenomena connected therewith; (2) combustion of carbonaceous meteorites in the higher regions of the atmosphere; (3) combustion and decay of organic bodies; (4) decomposition of carbonates; (5) liberation of carbonic acid mechanically inclosed in minerals on their fracture or decomposition. ”

“ Oxygen and nitrogen are free as air, and as we have seen in the second chapter, their direct combination by the electric spark is possible. Hydrogen is free in the form of water but expensive to extricate by means of the electric current. But we need more carbon than anything else and where shall we get that? Bits of crystallized carbon can be picked up in South Africa and elsewhere, but those who can afford to buy them prefer to wear them rather than use them in making synthetic food. Graphite is rare and hard to melt. We must then have recourse to the compounds of carbon. ”