Chapter XXIII: Carbon

Carbon exists in nature in a multitude of forms. It is rarely found in the pure and uncombined condition, though certain well-known substances possess it in large quantity.

Ordinary Charcoal.

Probably the most familiar and representative form of carbon is that known as charcoal. But charcoal is rarely free from other chemical elements, and a distinction ought to be made between it and the absolutely pure form of the element under consideration. Charcoal is produced by the partial decomposition, under the influence of heat, of vegetable or animal substances. Thus charcoal is commonly prepared by piling wood into a conical heap, then covering it with earth and sods, and finally setting it on fire within. Certain portions of the wood are thus burned, while others are only charred. The wood is decomposed by the heat to which it is subjected; volatile materials generated by this decomposition are expelled, while there is left behind a solid matter consisting mainly of carbon, and called charcoal.

Animal Charcoal.

The same general treatment of certain animal matters, such as waste leather, gives rise to a finer kind of carbon called animal charcoal.

Again, when bones are partly burned, they produce what is called bone-coal. The _mineral matter_ of the bone undergoes no change by the heat; but the gelatinous matters which permeate it are decomposed, and they leave behind them the carbon deposited upon this mineral matter.

Lamp-Black.

Another material, closely assimilated to those already spoken of, is lamp-black. This is a product of the imperfect combustion of substances like oil, tar, resin, and the like, which are very rich in carbon. The tar or resin being set on fire is allowed to burn, but in an imperfect way, and so as to evolve a dense black smoke. The smoke flows into a chamber prepared for it, where the sooty material collects on the floor and walls. It is afterwards scraped up and put into packages for commercial distribution. In the English method of manufacture of lamp-black, the smoke is made to pass through a series of heavy canvas bags. From openings at the bottoms of the bags, the soot is afterward drawn out for packing.

Coal.

Anthracite coal and bituminous coal are both well-known compounds of carbon. Anthracite seems to be derived from bituminous coal which has been subjected in the earth to heat and pressure under conditions favorable to the expulsion of some of the more volatile constituents of the original bituminous coal. Both of these combustibles, when carefully studied, show distinct evidences of their vegetable origin. Plainly they are accumulated masses of the remains of a rank vegetation which flourished in an earlier period in the geological history of our globe. Careful observations made in the mines have revealed in the coal the existence of trunks of trees, branches, leaves, fruits, in various conditions from the one extreme of comparatively perfect preservation, to the other extreme in which the mineral preserves a mere impression of the original vegetable matter. These remains have made it possible to construct a complete botany of this period of geological history; and with but a moderate aid of the imagination, artists have been able to produce ideal landscapes representing these early forms of vegetable life as they flourished in the ancient ages.

Graphite.

Closely allied to anthracite coal is that valuable material called graphite. This a very compact and comparatively pure form of carbon. It is familiarly known to every one in the black material used in lead pencils. Graphite is commonly called black lead, though it is a well established fact that it contains no lead at all. Strangely enough graphite is remarkably incombustible under all ordinary circumstances. It is also—like other forms of carbon—infusible at the highest temperatures known. On account of these properties graphite finds use, though it must be deemed a somewhat anomalous one, in the manufacture of crucibles. When the precious metals are fused in such a crucible, at a high temperature in a glowing furnace, an interesting paradox is furnished. It is this: the coal—freely burning in the fire, and so furnishing the intense heat desired—is fundamentally of precisely the same chemical nature as the graphite of the crucible, which resists the heat and the combustion, and, while allowing the metals to melt, preserves them.

The Diamond.

The diamond is nearly pure carbon, crystallized. Perhaps it is not too much to say that it is the most striking and wonderful of all the forms of this interesting element. The costliness of the diamond is referable largely to its great rarity; for it is found in comparatively few portions of the earth.

The ancient Greeks and Romans highly prized the rare and precious crystal, which they obtained from India, and it was worn by them not only because of its costliness and beauty, but also because they believed that it served as a potent charm against alarms and enchantments; more important yet, they ascribed to it the power of preserving the peace and harmony of the family circle. Upon this point a French writer has wittily said: “Cette dernière vertu, je crois qu’il la possède encore quand le mari est assez riche pour acheter le bijou que sa femme ambitionne de porter!”

The East Indies, the Cape of Good Hope and the Brazils may be said to be the principal sources of this gem. In Brazil the search for diamonds is systematically conducted. The diamond bearing soils are carefully pulverized in vessels of water, under the direction of experienced inspectors. The work is done by slaves who prosecute their search under the stimulus of the well understood rule that he who finds a diamond weighing seventeen and one-half carats or more, publicly receives his freedom as a reward. Notwithstanding the systematic labor applied to the search for these gems and the fascination naturally attending undertakings of this sort, the wealth of Brazil is derived to a vastly greater extent from its agricultural products than from its mines. Thus it is stated that from 1740 to 1822, a period of more than eighty years, the diamond mines yielded but little more than $17,000,000. On the other hand the value of coffee exported in a single year has sometimes been double or even more than double this amount. Thus in the year 1859 the coffee exported was valued at above $28,000,000; and in 1873 the quantity of this article exported was valued at above $60,000,000.

The great diamonds of the world (natural size).]

The larger gems are exceedingly rare. On this account the money value of diamonds increases in a far more rapid ratio than the weight.

The Cutting of Diamonds.

The cutting of diamonds as an art has been known for but a few centuries, and the perfection with which it is at present conducted is of much more recent date. Of course the process is an extremely delicate and important one because it involves splitting off portions of the gem so as to reduce it to the exact geometrical shape previously decided upon. That form called the _brilliant_ is the one commonest produced at the present day. The business of cutting diamonds has been for a long time concentrated in the city of Amsterdam in Holland. Here, among a Jewish population of twenty-eight thousand persons, ten thousand are employed exclusively in working on diamonds. In many cases diamonds are subject to a very large relative loss of weight by the process of cutting. Thus the Koh-i-noor, when brought from India as a gift from the East India Company to the English Crown, was in the rough state and weighed one hundred and eighty-six carats. It was afterwards cut in Amsterdam, by which process it suffered a loss of weight variously stated as from eighty to one hundred carats. After the first trimming, the gem is carefully polished by rubbing it gently against a revolving plate upon which is a mixture of oil and diamond dust.

Up to the close of the last century the nature and composition of the diamond had been a subject of interesting discussion among students of natural science. At the period mentioned however, the question was settled by Lavoisier and other scientific investigators, who clearly proved that the diamond underwent complete combustion in oxygen and that as a result carbon dioxide gas was generated.

Other Natural Forms of Carbon.

In addition to the well-known forms of matter containing carbon, and already described, there are yet many others.

Thus it is found in the atmosphere, as has already been explained, in the form of carbon dioxide. This gas exists in the air in small relative proportion, but in enormous aggregate amount.

As a natural carbonaceous substance petroleum, too, ought not to be forgotten. This wonderful and useful substance stored up beneath the surface of the earth, in incredibly large quantities, owes its chief value to its wealth of carbon. It is composed of carbon and hydrogen, but the former is the constituent to which is referable the beautiful light it affords.

Again, the marble and the limestones of the globe contain enormous quantities of carbon. These minerals consist principally of calcic carbonate (Ca CO₃); and the carbon makes up about one-eight of this substance. Since some whole mountain chains consist chiefly of limestone or marble, it is plain that the total amount of carbon in these forms must be very large.

With few exceptions, all animal and vegetable matters contain carbon—a substance which appears to perform its most important offices in connection with the kingdoms of life. Indeed it has been called the characteristic element of animal and vegetable compounds. So vast is the variety of these compounds already recognized that it is hardly conceivable that man can ever be able to acquire an acquaintance with all those as yet undetected.

Infusibility of Carbon.

Carbon differs from most solid substances in the fact that it is infusible at the highest temperatures to which it has yet been subjected. And since in the elementary form it has not been changed to the liquid state, much less has it been brought to the _gaseous_ condition. Indeed this stability and fixedness of carbon is one of its most valuable attributes. Thus this characteristic is a principal one that renders it specially appropriate for use in the pencils employed in electric lighting. It is true these pencils slowly burn away. But some combustion ought to be expected when it is remembered that the electric current, flowing from one pencil to the other, affords an intense heat as well as brilliant light. But it is a general law that substances give out the most intensely brilliant white light when they neither liquefy nor volatilize, and to this principle—exemplified in the carbon pencils—must be referred the brilliancy of the electric light.

Decolorizing Power of Carbon.

Carbon, whether in the form of wood charcoal, animal charcoal, or bone-coal, has a wonderful power of decolorizing liquids. Even more compact carbonaceous matter, such as anthracite coal, possesses this same property though, as might be expected, to a much inferior degree. Thus if a colored solution is strained through a considerable quantity of one of these forms of carbon, the latter substance absorbs the coloring matter and the liquid passes through practically colorless. On account of this wonderful power bone-coal is used in the arts in enormous quantity in many processes where liquids must be decolorized. The sugar refining industry affords a prominent example upon this point. Here, enormous quantities of bone-coal are used for the purpose of whitening the syrups before crystallizing the sugar.

Charcoal has also a similar, and yet more striking, property of absorbing offensive gases. Thus, tainted meat packed in freshly burned charcoal quickly loses its odor—which is absorbed by the coal—and the meat then becomes sweet and wholesome.

Chemical Properties of Carbon.

The chemical properties of carbon are by no means less wonderful than the characteristics already referred to. It is very inert at low temperatures; but at high temperatures, it manifests chemical activities of extraordinary vigor. Thus at high temperatures carbon withdraws oxygen from almost any other elements known, in this way manifesting chemical force superior to that possessed by any of them.

The Great Number of Compounds Formed by Carbon.

The vast number of the compounds of carbon seems to be referable to two fundamental properties with which it is endowed by nature. One of these is the fact that the atom of carbon possesses four points of attraction. This matter need not be explained here as it has already been discussed at sufficient length. But the fact may be conveniently represented to the eye by a symbol like the following:

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——C——
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The other property referred to is this: carbon—unlike most other elements—has a peculiar capacity by virtue of which atoms of it may join together in either short or long chains, and afterwards may gather other elements to the various parts of the chain. One among the many ways in which carbon takes part in forming such compounds may be represented by the simple diagram shown in the margin:

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——C——
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——C——
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——C——
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——C——
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——C——
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The number of compounds of this character already known to chemists is very large; it suggests the probability that there is no distinct limit to the number of atoms that may be linked in a continuous chain in this way. Moreover a given chain may have attached upon its sides or ends one or more additional chains of elements or compounds and thus give rise to an all but infinite number of substances with almost infinitely varied properties.

READING REFERENCES.

Coal, and the Coal-mines of Pennsylvania.
=Harper’s= Magazine. xv, 451.

Diamonds.
=Scribner’s= Monthly. v, 529.
=Harper’s= Magazine. xix, 466; xxxii, 343.

Diamond Fields of South Africa.
=Harper’s= Magazine. xlvi, 321.