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.
[Illustration: FIG. 61.—Charcoal pit.]
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.
[Illustration: FIG. 62.—Tree trunks discovered in coal mines.]
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.
[Illustration: FIG. 63.—Charcoal burners at work.]
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.
[Illustration: FIG. 64.—Manufacture of lamp-black.]
[Illustration: FIG. 65.—Bags in which lamp-black is collected in the
English process of manufacture.]
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.
[Illustration: FIG. 66.—Imaginary landscape during the carboniferous
era.]
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.
[Illustration: FIG. 68.—“The Sancy.”]
[Illustration: FIG. 69.—“The Polar Star.”]
[Illustration: FIG. 70.—“The Empress Eugenie” or “Pigott.”]
[Illustration: FIG. 71.—“The Koh-i-noor.”]
[Illustration: FIG. 72.—“The Star of the South.”]
[Illustration: FIG. 73.—“The Regent” or “Pitt.”]
[Illustration: FIG. 74.—“The Grand Duke of Tuscany.”]
[Illustration: FIG. 75.—“The Orloff.”]
[Illustration: FIG. 76.—“The Grand Mogul.”
The great diamonds of the world (natural size).]
[Illustration: FIG. 77.—Transportation of diamonds under military
protection.]
[Illustration: FIG. 79.—Diamond cutter at work.]
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.
[Illustration: FIG. 80.—Diamond known as “The Star of the South”;
before and after cutting.]
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.
[Illustration: FIG. 81.—Diamond polisher at work.]
[Illustration: FIG. 67.—Diamond washing in Brazil.]
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.
[Illustration: FIG. 82.—The Koh-i-noor before cutting.]
[Illustration: FIG. 83.—The Koh-i-noor after cutting.]
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.
[Illustration: FIG. 84.—View in the vicinity of the Pennsylvania oil
wells.]
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.
[Illustration: FIG. 85.—Automatic regulator whereby the carbon pencils
of the electric light are maintained at the proper distance apart.]
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.
[Illustration: FIG. 86.—Magnified view of the carbon terminals used for
the production of the electric light.]
[Illustration: FIG. 87.—Excavations carried on at night by aid of the
electric light.]
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.
[Illustration: FIG. 88.—Colored liquid filtered through charcoal, and
thereby decolorized.]
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:
|
——C——
|
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:
|
——C——
|
——C——
|
——C——
|
——C——
|
——C——
|
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.