Chapter VIII: Carbon and the Hydrocarbons (1)

It is necessary to clearly distinguish between the two closely-allied terms, charcoal and carbon. Charcoal is well known to everybody, although it is no easy matter to obtain it in a chemically pure state. Pure charcoal is a simple, insoluble, infusible, combustible substance produced by heating organic matter, and has the familiar aspect of a black mass, devoid of any crystalline structure, and completely insoluble. Charcoal is a substance possessing a peculiar combination of physical and chemical properties. This substance, whilst in a state of ignition, combines directly with oxygen; in organic substances it is found in combination with hydrogen, oxygen, nitrogen, and sulphur. But in all these combinations there is no real charcoal, as in the same sense there is no ice in steam. What is found in such combinations is termed 'carbon'--that is, an element common to charcoal, to those substances which can be formed from it, and also to those substances from which it can be obtained. Carbon may take the form of charcoal, but occurs also as diamond and as graphite. Truly no other element has such a wide terminology. Oxygen is always called 'oxygen,' whether it is in a free gaseous state, or in the form of ozone, or oxygen in water, or in nitric acid or in carbonic anhydride. But here there is some confusion. In water it is evident that there is no oxygen in a gaseous form, such as can be obtained in a free state, no oxygen in the form of ozone, but a substance which is capable of producing both oxygen, ozone, and water. As an element, oxygen possesses a known chemical individuality, and an influence on the properties of those combinations into which it enters. Hydrogen gas is a substance which reacts with difficulty, but the element hydrogen represents in its combinations an easily displaceable component part. Carbon may be considered as an atom of carbon matter, and charcoal as a collection of such atoms forming a whole substance, or mass of molecules of the substance. The accepted atomic weight of carbon is 12, because that is the least quantity of carbon which enters into combination in molecules of its compounds; but the weight of the molecules of charcoal is probably very much greater. This weight remains unknown because charcoal is capable of but few direct reactions and those only at a high temperature (when the weight of its molecules probably changes, as when ozone changes into oxygen), and it does not turn into vapour. Carbon exists in nature, both in a free and combined state, in most varied forms and aspects. Carbon in a free state is found in at least three different forms, as charcoal, graphite, and the diamond. In a combined state it enters into the composition of what are called organic substances--a multitude of substances which are found in all plants and animals. It exists as carbonic anhydride both in air and in water, and in the soil and crust of the earth as salts of carbonic acid and as organic remains.

The variety of the substances of which the structure of plants and animals is built up is familiar to all. Wax, oil, turpentine, and tar, cotton and albumin, the tissue of plants and the muscular fibre of animals, vinegar and starch, are all vegetable and animal matters, and all carbon compounds.[1] The class of carbon compounds is so vast that it forms a separate branch of chemistry, known under the name of organic chemistry--that is, the chemistry of carbon compounds, or, more strictly, of the hydrocarbons and their derivatives.

[1] Wood is the non-vital part of ligneous plants: the vital part of
ordinary trees is situated between the bark and the lignin. Every
year a layer of lignin is deposited on this part by the juices
which are absorbed by the roots and drawn up by the leaves; for
this reason the age of trees may be determined by the number of
lignin layers deposited. The woody matter consists principally
of fibrous tissue on to which the lignin or so-called incrusting
matter has been deposited. The tissue has the composition
C_{6}H_{10}O_{5}, the substance deposited on it contains more
carbon and hydrogen and less oxygen. This matter is saturated
with moisture when the wood is in a fresh state. Fresh birch wood
contains about 31 p.c. of water, lime wood 47 p.c., oak 35 p.c.,
pine and fir about 37 p.c. When dried in the air the wood loses a
considerable quantity of water and not more than 19 p.c. remains.
By artificial means this loss of water may be increased. If water
be driven into the pores of wood the latter becomes heavier than
water, as the lignin of which it is composed has a density of
about 1·6. One cubic centimetre of birch wood does not weigh more
than 0·901 gram, fir 0·894, lime tree 0·817, poplar 0·765 when
in a fresh state; when in a dry state birch weighs 0·622, pine
0·550, fir 0·355, lime 0·430, guaiacum 1·342, ebony 1·226. On one
hectare (2·7 acres) of woodland the yearly growth averages the
amount of 3,000 kilograms (or about 3 tons) of wood, but rarely
reaches as much as 5,000 kilos. The average chemical composition
of wood dried in air may be expressed as follows:--Hygroscopic
water 15 p.c., carbon 42 p.c., hydrogen 5 p.c., oxygen and
nitrogen 37 p.c., ash 1 p.c. Wood parts with its hygroscopic water
at 150°, and decomposes at about 300°, giving a brown, brittle,
so-called red charcoal; above 350° black charcoal is produced.
As the hydrogen contained in wood requires for its combustion
about forty parts by weight of oxygen, which is present to the
amount of about 36 p.c., all that burns of the wood is the carbon
which it contains, 100 parts of wood only giving out as much heat
as forty parts of charcoal, and therefore it would be far more
profitable to use charcoal for heating purposes than wood, if it
were possible to obtain it in such quantities as correspond with
its percentage ratio--that is forty parts per 100 parts of wood.
Generally, however, the quantity produced is far less, not more
than 30 p.c., because part of the carbon is given off as gas, tar,
&c. If wood has to be transported great distances, or if it is
necessary to obtain a very high temperature by burning it, then
even as little as 25 p.c. of charcoal from 100 parts of wood may be
advantageous. Charcoal (from wood) develops on burning 8,000 heat
units, whilst wood dried in air does not develop more than 2,800
units of heat; therefore seven parts of charcoal give as much heat
as twenty parts of wood. As regards the temperature of combustion,
it is far higher with charcoal than with wood, because twenty parts
of burning wood give, besides the carbonic anhydride which is also
formed together with charcoal, eleven parts of water, the
evaporation of which requires a considerable amount of heat.

The composition of the growing parts of plants, the leaves, young
branches, shoots, &c., differs from the composition of the wood
in that these vital parts contain a considerable quantity of sap
which contains much nitrogenous matter (in the wood itself there
is very little), mineral salts, and a large amount of water.
Taking, for example, the composition of clover and pasture hay in
the green and dry state; in 100 parts of green clover there is
about 80 p.c. of water and 20 p.c. of dry matter, in which there
are about 3·5 parts of nitrogenous albuminous matter, about 9·5
parts of soluble and about 5 parts of insoluble non-nitrogenous
matter, and about 2 p.c. of ash. In dry clover or clover-hay there
is about 15 p.c. of water, 13 p.c. of nitrogenous matter, and 7
p.c. of ash. This composition of grassy substances shows that they
are capable of forming the same sort of charcoal as wood itself.
It also shows the difference of nutritive properties existing
between wood and the substances mentioned. These latter serve as
food for animals, because they contain those substances which are
capable of being dissolved (entering into the blood) and forming
the body of animals; such substances are proteids, starch, &c. Let
us remark here that with a good harvest an acre of land gives in
the form of grass as much organic substance as it yields in the
form of wood.

One hundred parts of dry wood are capable of giving, on dry
distillation, besides 25 p.c. of charcoal and 10 p.c. or more of
tar, 40 p.c. of watery liquid, containing acetic acid and wood
spirit, and about 25 p.c. of gases, which may be used for heating
or lighting purposes, because they do not differ from ordinary
illuminating gas, which can indeed be obtained from wood. As
wood-charcoal and tar are valuable products, in some cases the
dry distillation of wood is carried on principally for producing
them. For this purpose those kinds of woods are particularly
advantageous which contain resinous substances, especially
coniferous trees, such as fir, pine, &c.; birch, oak, and ash
give much less tar, but on the other hand they yield more aqueous
liquor. The latter is used for the manufacture of wood spirit,
CH_{4}O, and acetic acid, C_{2}H_{4}O_{2}. In such cases, the
dry distillation is carried on in stills. The stills are nothing
more than horizontal or vertical cylindrical retorts, made of
boiler plate, heated with fuel and having apertures at the top
and sometimes also at the bottom for the exit of the light and
heavy products of distillation. The dry distillation of wood in
stoves is carried on in two ways, either by burning a portion of
the wood inside the stove in order to submit the remainder to dry
distillation by means of the heat obtained in this manner, or by
placing the wood in a stove the thin sides of which are surrounded
with a flue leading from the fuel, placed in a space below.

The first method does not give such a large amount of liquid
products of the dry distillation as the latter. In the latter
process there is generally an outlet below for emptying out the
charcoal at the close of the operation. For the dry distillation
of 100 parts of wood from forty to twenty parts of fuel are used.

In the north of Russia wood is so plentiful and cheap that this
locality is admirably fitted to become the centre of a general
trade in the products of its dry distillation. Coal (Note 6),
sea-weed, turf, animal substances (Chapter VI.), &c., are also
submitted to the process of dry distillation.

If any one of these organic compounds be strongly heated without free access of air--or, better still, in a vacuum--it decomposes with more or less facility. If the supply of air be insufficient, or the temperature be too low for combustion (_see_ Chapter III.), and if the first volatile products of transformation of the organic matter are subjected to condensation (for example, if the door of a stove be opened), an imperfect combustion takes place, and smoke, with charcoal or soot, is formed.[2] The nature of the phenomenon, and the products arising from it, are the same as those produced by heating alone, since that part which is in a state of combustion serves to heat the remainder of the fuel. The decomposition which takes place on heating a compound composed of carbon, hydrogen, and oxygen is as follows:--A part of the hydrogen is separated in a gaseous state, another part in combination with oxygen, and a third part separates in combination with carbon, and sometimes in combination with carbon and oxygen in the form of gaseous or volatile products, or, as they are also called, the products of dry distillation. If the vapours of these products are passed through a strongly heated tube, they are changed again in a similar manner and finally resolve themselves into hydrogen and charcoal. Altogether these various products of decomposition contain a smaller amount of carbon than the original organic matter; part of the carbon remains in a free state, forming charcoal.[3] It remains in that space where the decomposition took place, in the shape of the black, infusible, non-volatile charcoal familiar to all. The earthy matter and all non-volatile substances (ash) forming a part of the organic matter, remain behind with the charcoal. The tar-like substances, which require a high temperature in order to decompose them, also remain mixed with charcoal. If a volatile organic substance, such as a gaseous compound containing oxygen and hydrogen, be taken, the carbon separates on passing the vapour through a tube heated to a high temperature. Organic substances when burning with an insufficient supply of air give off soot--that is, charcoal--proceeding from carbon compounds in a state of vapour, the hydrogen of which has, by combustion, been converted into water; so, for instance, turpentine, naphthalene, and other hydrocarbons which are with difficulty decomposed by heat, easily yield carbon in the form of soot during combustion. Chlorine and other substances which, like oxygen, are capable of taking up hydrogen, and also substances which are capable of taking up water, can also separate carbon from (or char) most organic substances.

[2] The result of imperfect combustion is not only the loss of a part
of the fuel and the production of smoke, which in some respects
is inconvenient and injurious to health, but also a low flame
temperature, which means that a less amount of heat is transmitted
to the object heated. Imperfect combustion is not only always
accompanied by the formation of soot or unburnt particles of
charcoal, but also by that of carbonic oxide, CO, in the smoke
(Chapter IX.) which burns, emitting much heat. In works and
factories where large quantities of fuel are consumed, many
appliances are adopted to ensure perfect combustion, and to combat
against such a ruinous practice as the imperfect combustion of
fuel. The most effective and radical means consists in employing
combustible gases (producer and water gases), because by their
aid perfect combustion can be easily realised without a loss of
heat-producing power and the highest temperature can be reached.
When solid fuel is used (such as coal, wood, and turf), imperfect
combustion is most liable to occur when the furnace doors are
opened for the introduction of fresh fuel. The step furnace may
often prove a remedy for this defect. In the ordinary furnace
fresh fuel is placed on the burning fuel, and the products of dry
distillation of the fresh fuel have to burn at the expense of
the oxygen remaining uncombined with the burnt fuel. Imperfect
combustion is observed in this case also from the fact that the
dry distillation and evaporation of the water of the fresh fuel
lying on the top of that burnt, lowers the temperature of the
flame, because part of the heat becomes latent. On this account a
large amount of smoke (imperfect combustion) is observed when a
fresh quantity of fuel is introduced into the furnace. This may
be obviated by constructing the furnace (or managing the stoking)
in such a way that the products of distillation pass through
the red-hot charcoal remaining from the burnt fuel. It is only
necessary in order to ensure this to allow a sufficient quantity
of air for perfect combustion. All this may be easily attained
by the use of step fire-bars. The fuel is fed into a hopper and
falls on to the fire-bars, which are arranged in the form of a
staircase. The burning charcoal is below, and hence the flame
formed by the fresh fuel is heated by the contact of the red-hot
burning charcoal. An air supply through the fire grate, an equal
distribution of the fuel on the fire-bars (otherwise the air will
blow through empty spaces and lower the temperature), a proper
proportion between the supply of air and the chimney draught,
and a perfect admixture of air with the flame (without an undue
excess of air), are the means by which we can contend against the
imperfect combustion of such kinds of fuel as wood, peat, and
ordinary (smoky) coal. Coke, charcoal, anthracite, burn without
smoke, because they do not contain hydrogenous substances which
furnish the products of dry distillation, but imperfect combustion
may occur with them also; in that case the smoke contains carbonic
oxide.

[3] Under the action of air, organic substances are capable of
oxidising to such an extent that all the carbon and all the
hydrogen they contain will be transformed into carbonic anhydride
and water. The refuse of plants and that of animals are subjected
to such a change whether they slowly decompose and putrefy, or
rapidly burn with direct access of air. But if the supply of air
be limited, there can be no complete transformation into water and
carbonic anhydride, there will be other volatile matters (rich in
hydrogen), while charcoal must remain as a non-volatile substance.
All organic substances are unstable, they do not resist heat, and
change even at ordinary temperatures, particularly if water be
present. It is therefore easy to understand that charcoal may in
many cases be obtained through the transformation of substances
entering into the composition of organisms, but that it is never
found in a pure state.

However, water and carbonic anhydride are not the only products
separated from organic substances. Carbon, hydrogen, and oxygen
are capable of giving a multitude of compounds; some of these
are volatile compounds, gaseous, soluble in water--they are
carried off from organic matter, undergoing change without access
of air. Others, on the contrary, are non-volatile, rich in
carbon, unaffected by heat and other agents. The latter remain
in admixture with charcoal in the place where the decomposition
takes place; such, for example, are tarry substances. The quantity
of those bodies which are found mixed with the charcoal is very
varied, and depends on the energy and duration of the decomposing
agent. The annexed table shows, according to the data of Violette,
those changes which wood undergoes at various temperatures when
submitted to dry distillation by means of superheated steam:--

+----------------------------+------------------------------+
| Residue | |
|Temperature from 100 parts | In 100 parts of the residual |
| of alder wood | charcoal |
+----------------------------+---------------------+--------+
| | C H O and N | Ash |
| 150° 100·0 | 47·5 6·1 46·3 | 0·1 |
| 350° 29·7 | 76·6 4·1 18·4 | 0·6 |
| 1032° 18·7 | 81·9 2·3 14·1 | 1·6 |
| 1500° 17·3 | 95·0 0·7 3·8 | 1·7 |
+----------------------------+---------------------+--------+

Wood charcoal is prepared in large quantities in a similar manner--that is, by the partial combustion of wood.[4] In nature a similar process of carbonisation of vegetable refuse takes place in its transformation under water, as shown by the marshy vegetation which forms peat.[5] In this manner doubtless the enormous masses of coal were formed[6] which, following the example set by England, are now utilised everywhere as the principal material for heating steam boilers, and in general for all purposes of heating and burning.[7] Russia possesses many very rich coalfields, amongst which the Donetz district is most worthy of remark.[8]

[4] The object of producing charcoal from wood has been explained in
Note 1. _Wood charcoal_ is obtained in so-called stacks by
partially burning the wood, or by means of dry distillation (Note
1) without the access of air. It is principally manufactured for
metallurgical processes, especially for smelting and forging
iron. The preparation of charcoal in stacks has one advantage,
and that is that it may be done on any spot in the forest. But
in this way all the products of dry distillation are lost.
For charcoal burning, a pile or stack is generally built, in
which the logs are placed close together, either horizontally,
vertically, or inclined, forming a stack of from six to fifty
feet in diameter and even larger. Under the stack are several
horizontal air passages, and an opening in the middle to let out
the smoke. The surface of the stack is covered with earth and
sods to a considerable thickness, especially the upper part, in
order to hinder the free passage of air and to concentrate the
heat inside. When the stack is kindled, the pile begins to settle
down by degrees, and it is then necessary to look after the turf
casing and keep it in repair. As the combustion spreads throughout
the whole pile, the temperature rises and real dry distillation
commences. It is then necessary to stop the air holes, in order as
much as possible to prevent unnecessary combustion. The nature of
the process is, that part of the fuel burns and develops the heat
required for subjecting the remainder to dry distillation. The
charring is stopped when the products of dry distillation, which
are emitted, no longer burn with a brilliant flame, but the pale
blue flame of carbonic oxide appears. Dry wood in stacks yields
about one-fourth of its weight of charcoal.

[5] When dead vegetable matter undergoes transformation in air, in the
presence of moisture and lower organisms, there remains a
substance much richer in carbon--namely, humus, black earth or
mould. 100 parts of humus in a dry state contain about 70 p.c.
of carbon. The roots, leaves, and stems of plants which wither
and fall to the ground form a soil rich in humus. The non-vital
vegetable substances (ligneous tissue) first form brown matter
(ulmic compounds), and then black matter (humic substances),
which are both insoluble in water; after this a brown acid is
produced, which is soluble in water (apocrenic acid), and lastly
a colourless acid also soluble in water (crenic acid). Alkali
dissolves a part of the original brown and black substances,
forming solutions of a brown tint (ulmic and humic acids) which
sometimes communicate their colour to springs and rivers. The
proportion of humus in soil generally has a direct influence on
its fertility; firstly, because putrefying plants develop carbonic
anhydride and ammonia, and yield the substances forming the ashes
of plants, which are necessary to vegetation; secondly, because
humus is capable of attracting the moisture of the air and of
absorbing water (twice its weight) and in this way keeps the soil
in a damp condition, which is indispensable for nourishment;
thirdly, humus renders the soil porous, and, fourthly, it renders
it more capable of absorbing the heat of the sun's rays. On this
account black earth is often most remarkable for its fertility.
One object of manuring is to increase the quantity of humus in the
soil, and any easily changeable vegetable or any animal matter
(composts) may be used. The boundless tracts of black earth soil
in Russia are capable of bestowing countless wealth on the country.

The origin and extent of black earth soil are treated in detail in
Professor Dokouchaeff's works.

If those substances which produce humus undergo decomposition
under water, less carbonic anhydride is formed, a quantity of
marsh gas, CH_{4}, is evolved, and the solid residue forms
an acid humus found in great quantities in marshy places and
called _peat_. Peat is especially abundant in the lowlands of
Holland, North Germany, Ireland, and Bavaria. In Russia it is
likewise found in large quantities, especially in the North-West
districts. The old hard forms of peat resemble in composition and
properties brown coal; the newest formations, as yet unhardened
by pressure, form very porous masses which retain traces of the
vegetable matter from which they have been formed. Dried (and
sometimes pressed) peat is used as fuel. The composition of peat
varies considerably with the locality in which it is found. When
dried in air it does not contain less than 15 p.c. of water and
8 p.c. of ash; the remainder consists of 45 p.c. of carbon, 4
p.c. of hydrogen, 1 p.c. of nitrogen, and 28 p.c. of oxygen. Its
heating power is about equivalent to that of wood. The brown
earthy varieties of coal were probably formed from peat. In other
cases they have a marked woody structure, and are then known as
lignites. The composition of the brown sorts of coal resembles in
a marked degree that of peat--namely, in a dried state brown coal
contains on an average 60 p.c. of carbon, 5 p.c. of hydrogen, 26
p.c. of oxygen and nitrogen, and 9 p.c. of ash. In Russia brown
coal is met with in many districts near Moscow, in the Governments
of Toula and Tver and the neighbourhood; it is very usually used
as fuel, particularly when found in thick seams. The brown coals
usually burn with a flame like wood and peat, and are akin to them
in heating power, which is half or a third that of the best coal.

[6] Grass and wood, the vegetation of primæval seas and similar refuse
of all geological periods, must have been in many cases subjected
to the same changes they now undergo--that is, under water they
formed peat and lignites. Such substances, preserved or a long
time underground, subjected to the action of water, compressed by
the new strata formed above them, transformed by the separation
of their more volatile component parts (peat and lignites, even
in their last condition, still continue to evolve nitrogen,
carbonic anhydride, and marsh gases) form _coal_. Coal is a
dense homogeneous mass, black, with an oily or glassy lustre, or
more rarely dull without any evident vegetable structure; this
distinguishes it in appearance from the majority of lignites.
The density of coal (not counting the admixture of pyrites,
&c.) varies from 1·25 (dry bituminous coal) to 1·6 (anthracite,
flameless), and even reaches 1·9 in the very dense variety of
coal found in the Olonetzky government (termed shungite), which
according to the investigations of Professor Inostrantzeff may be
regarded as the extreme member of the various forms of coal.

In order to explain the formation of coal from vegetable matter,
Cagniard de la Tour enclosed pieces of dried wood in a tube and
heated them to the boiling point of mercury, when the wood was
changed into a semi-liquid black mass from which a substance
exceedingly like coal separated. In this manner some kinds of
wood formed coal which on being heated left caking coke, others
non-caking; precisely as we find with the natural varieties of
coal. Violette repeated these experiments with wood dried at
150°, and showed that when wood is decomposed in this way, a
gas, an aqueous liquor, and a residue are formed. The latter
at a temperature of 200° has the properties of wood charcoal
incompletely burnt; at 300° and higher a homogeneous mass like
coal is formed which at 340° is dense and without cavities. At
400° the residue resembles anthracite. In nature probably the
decomposition was in rare cases effected by heat alone; more
generally it was effected by means of water and heat, but in
either case the result ought to be almost the same.

The average composition of coal compiled from many analyses,
disregarding the ash, is as follows: 84 parts of carbon, 5 parts
of hydrogen, 1 part of nitrogen, 8 parts of oxygen, 2 of sulphur.
The quantity of ash is on an average 5 p.c., but there are coals
which contain a larger quantity, and naturally they are not so
advantageous for use as fuel. The amount of water does not usually
exceed more than 10 p.c. The _anthracites_ form a remarkable
variety of coals, they do not give any volatile products, or but
a very small amount, as they contain but little hydrogen compared
to oxygen. In the average composition of coal we saw that for 5
parts of hydrogen there were 8 parts of oxygen; therefore 4 parts
by weight of hydrogen are capable of forming hydrocarbons, because
1 part of hydrogen is necessary in order to form water with the 8
parts of oxygen. These 4 parts by weight of hydrogen can convert
48 parts of carbon into volatile products, because 1 part of
hydrogen by weight in these substances combines with 12 parts of
carbon. The anthracites differ essentially from this: neglecting
the ash, their average composition is as follows: 94 parts of
carbon, 3 of hydrogen, and 3 of oxygen and nitrogen. According to
the analyses of A. A. Voskresensky, the Grousheffsky anthracite
(Don district) contains: C = 93·8, H = 1·7, ash = 1·5. Therefore
the anthracites contain but little hydrogen capable of combining
with the carbon to form hydrocarbons which burn with a flame.
Anthracites are the oldest forms of coal. The newest and least
transformed coals, which resemble some of the brown varieties, are
the _dry_ coals. They burn with a flame like wood, and leave a
coke having the appearance of lumps of coal, half their component
parts being absorbed by the flame (they contain much hydrogen and
oxygen). The remaining varieties of coal (gas coal, smithy coal,
coking, and anthracite) according to Grüner in all respects form
connecting links between the _dry_ coals and the anthracites.
These coals burn with a very smoky flame, and on being heated
leave _coke_, which bears the same relation to coal that charcoal
does to wood. The quantity and quality of coke vary considerably
with the different sorts of coal from which it is formed. In
practice coals are most often distinguished by the properties
and quantity of the coke which they give. In this particular the
so-called bituminous coals are especially valuable, as even the
slack of this kind gives on dry distillation large spongy masses
of coke. If large pieces of these kinds of coal are subjected
to dry distillation, they, as it were, melt, flow together, and
form caking masses of coke. The best coking coals give 65 p.c. of
dense caking coke. Such coal is very valuable for metallurgical
purposes (_see_ Note 8). Besides coke, the dry distillation of
coal produces gas (_see_ further, illuminating gas, p. 361),
coal-tar (which gives benzene, carbolic acid, naphthalene, tar
for artificial asphalt, &c.) and also an aqueous alkaline liquor
(with wood and lignites the liquid is acid from acetic acid) which
contains ammonium carbonate (_see_ Note 6).

[7] In England in 1850 the output of coal was as much as 48 million
tons, and in latter years it has risen to about 190 millions.
Besides this other countries contribute 300 millions--Russia about
6 millions. The United States of America come next to England with
an output of 160 million tons, then Germany 90 millions; France
produces but little (25 millions), and takes about 5 million tons
from England. Thus the world consumes about 500 million tons of
coal yearly. Besides household purposes, coal is chiefly used as
fuel for steam-engines. As every horse-power (= 75 kilogrammetres
per second) of a steam-engine expends on the average more than
25 kilograms in 24 hours, or in a year (counting stoppages) not
less than 5 tons per horse-power, and there are not less than 40
million horse-power at work in the world, the consumption of coal
for motive-power is at least equal to half the whole production.
For this reason coal serves as a criterion of the industrial
development of a country. About 15 p.c. of coal is used for the
manufacture of cast iron, wrought iron, steel, and articles made
of them.

[8] The principal coal beds of Russia under exploitation are: The Don
basin (150 million poods per annum, 62 poods = 1 ton), the Polish
basin (Dombrovo and others 120 million poods per annum), the Toula
and Riazan beds of the Moscow basin (up to 25 million poods),
the Ural basin (10 million poods), the Caucasian (Kviboul, near
Kutais), the Khirjhis steppes, the smithy coal basin (Gov. of
Tomsk), the Sahaline, &c. The Polish and Moscow basins do not give
any coking coals. The presence of every variety of coal (from
the dry coal near Lisichansk on the Donetz to the anthracites of
the entire south-east basin), the great abundance of excellent
metallurgical coal (coking, _see_ Note 6) in the western part
of the basin, its vast extent (as much as 25,000 sq. versts),
the proximity of the seams to the surface (the shafts are now
from 20 to 100 fathoms deep, and in England and Belgium as deep
as 500 fathoms), the fertility of the soil (black earth), the
proximity of the sea (about 100 versts from the Sea of Azoff) and
of the rivers Donetz, Don, and Dneiper, the most abundant seams
of excellent iron ore (Korsan Mogila, Krivoy Rog, Soulin, &c.,
&c.), copper ore, mercury ore (near Nikitovka, in the Bakhmouth
district of the Ekaterinoslav Gov.), and other ores, the richest
probably in the whole world, the beds of rock-salt (near the
stations of the Stoupka and Brianzovka) the excellent clay of all
kinds (china, fire-clay), gypsum, slate, sandstone, and other
_wealth of the Don coal basin_, give complete assurance of the
fact that with the growth of industrial activity in Russia this
bountiful land of the Cossacks and New Russia will become the
centre of the most extensive productive enterprise, not for the
requirements of Russia alone, but of the whole world, because in
no other place can be found such a concentration of favourable
conditions. The growth of enterprise and knowledge, together with
the extinction of the forests which compels Russia to foster the
production of coal, will help to bring about this desired result.
England with a whole fleet of merchant vessels exports annually
about 25 million tons of coal, the price of which is higher than
on the Donetz (where a pood of worked coal costs less than 5
copecks on the average), where anthracites and semi-anthracites
(like Cardiff or steam coal, which burns without smoke) and coking
and metallurgical coals are able both in quantity and quality to
satisfy the most fastidious requirements of the industry already
existing and rapidly increasing everywhere. The coal mines of
England and Belgium are approaching a state of exhaustion, whilst
in those of the Don basin, only at a depth of 100 fathoms,
1,200,000 million poods of coal lie waiting to be worked.

During the imperfect combustion of volatile substances containing carbon and hydrogen, the hydrogen and part of the carbon first burn, and the remainder of the carbon forms soot. Tar, pitch, and similar substances for this reason burn with a smoky flame. Thus soot is finely-divided charcoal separated during the imperfect combustion of the vapours and gases of carbonaceous substances rich in carbon. Specially-prepared soot (lampblack) is very largely used as a black paint and a large quantity goes for the manufacture of printers' ink. It is prepared by burning tar, oil, natural gas, naphtha, &c. The quantity of organic matter remaining undecomposed in the charcoal depends on the temperature to which it has been submitted. Charcoal prepared at the lowest temperature still contains a considerable quantity of hydrogen and oxygen--even as much as 4 p.c. of hydrogen and 20 p.c. of oxygen. Such charcoal still preserves the structure of the substance from which it was obtained. Ordinary charcoal, for instance, in which the structure of the tree is still visible, is of this kind. On submitting it to further heating, a fresh quantity of hydrogen with carbon and oxygen (in the form of gases or volatile matter) may be separated, and the purest charcoal will be obtained on submitting it to the greatest heat.[9] If it be required to prepare pure charcoal from soot it is necessary first to wash it with alcohol and ether in order to remove the soluble tarry products, and then submit it to a powerful heat to drive off the impurities containing hydrogen and oxygen. Charcoal however when completely purified does not change in appearance. Its porosity,[10] bad conducting power for heat, capability of absorbing the luminous rays (hence its blackness and opacity), and many other qualities, are familiar from everyday experience.[11] The specific gravity of charcoal varies from 1·4 to 1·9, and that it floats on water is due to the air contained in its pores. If charcoal is reduced to a powder and moistened with spirit, it immediately sinks in water. It is _infusible_ in the furnace and even at the temperature of the oxyhydrogen flame. In the heat generated by means of a powerful galvanic current charcoal only softens but does not completely melt, and on cooling it is found to have undergone a complete change both in properties and appearance, and is more or less transformed into graphite. The physical stability of charcoal is without doubt allied to its chemical stability. It is evidently a substance devoid of energy, for it is insoluble in all known liquids, and _at an ordinary temperature does not combine with anything_; it is an inactive substance, like nitrogen.[12] But these properties of charcoal change with a rise of temperature; thus, unlike nitrogen, charcoal, at a high temperature, combines directly with oxygen. This is well known, as charcoal burns in air. Indeed, not only does oxygen _combine with charcoal at a red heat_, but sulphur, hydrogen, silicon, and also iron and some other metals[12 bis] do so at a very high temperature--that is, when the molecules of the charcoal have reached a state of great instability--whilst at ordinary temperatures neither oxygen, sulphur, nor metals act on charcoal in any way. When burning in oxygen, charcoal forms carbonic anhydride, CO_{2}, whilst in the vapours of sulphur, carbon bisulphide, CS_{2}, is formed, and wrought iron, when acted on by carbon, becomes cast iron. At the great heat obtained by passing the galvanic current through carbon electrodes, charcoal combines with hydrogen, forming acetylene, C_{2}H_{2}. Charcoal does not combine directly with nitrogen, but in the presence of metals and alkaline oxides, nitrogen is absorbed, forming a metallic cyanide, as, for instance, potassium cyanide, KCN. From these few direct combinations which charcoal is capable of entering into, may be derived those numerous carbonaceous compounds which enter into the composition of plants and animals, and can be thus obtained artificially. Certain substances containing oxygen give up a part of it to charcoal at a relatively low temperature. For instance, nitric acid when boiled with charcoal gives carbonic anhydride and nitric peroxide. Sulphuric acid is reduced to sulphurous anhydride when heated with carbon. When heated to redness charcoal absorbs oxygen from a large number of the oxides. Even such oxides as those of sodium and potassium, when heated to redness, yield their oxygen to charcoal although they do not part with it to hydrogen. Only a few of the oxides, like silica (oxide of silicon) and lime (calcium oxide) resist the reducing action of charcoal. Charcoal is capable of changing its physical condition without undergoing any alteration in its essential chemical properties--that is, it passes into _isomeric_ or _allotropic forms_. The two other particular forms in which carbon appears are the _diamond_ and _graphite_. The identity of composition of these with charcoal is proved by burning an equal quantity of all three separately in oxygen (at a very high temperature), when each gives the same quantity of carbonic anhydride--namely, 12 parts of charcoal, diamond, or graphite in a pure state, yield on burning 44 parts by weight of carbonic anhydride. The physical properties present a marked contrast; the densest sorts of charcoal have a density of only 1·9, whilst the density of graphite is about 2·3, and that of the diamond 3·5. A great many other properties depend on the density, for instance combustibility. The lighter charcoal is, the more easily it burns; graphite burns with considerable difficulty even in oxygen, and the diamond burns only in oxygen and at a very high temperature. On burning, charcoal, the diamond, and graphite develop different quantities of heat. One part by weight of wood charcoal converted by burning into carbonic anhydride develops 8,080 heat units; dense charcoal separated in gas retorts develops 8,050 heat units; natural graphite, 7,800 heat units; and the diamond 7,770. The greater the density the less the heat evolved by the combustion of the carbon.[13]

[9] As it is difficult to separate from the charcoal the admixture of
ash--that is, the earthy matter contained in the vegetable
substance used for producing charcoal--in order to obtain it
in its purest condition it is necessary to use such organic
substances as do not contain any ash, for example completely
refined or purified crystallised sugar, crystallised tartaric
acid, &c.

[10] The cavities in charcoal are the passages through which those
volatile products formed at the same time as the charcoal have
passed. The degree of porosity of charcoal varies considerably,
and has a technical significance, in different kinds of charcoal.
The most porous charcoal is very light; a cubic metre of wood
charcoal weighs about 200 kilograms. Many of the properties of
charcoal which depend exclusively on its porosity are shared by
many other porous substances, and vary with the density of the
charcoal and depend on the way it was prepared. The property
which charcoal has of absorbing gases, liquids, and many
substances in solution, is a case in point. The densest kind
of charcoal is formed by the action of great heat on sugar and
other fusible substances. The lustrous grey dense coke formed in
gas retorts is also of this character. This dense coke collects
on the internal walls of the retorts subjected to great heat,
and is produced by the vapours and gases separated from the
heated coal in the retorts. In virtue of its density such coke
becomes a good conductor of the galvanic current and approaches
graphite. It is principally used in galvanic batteries. Coke, or
the charcoal remaining from the imperfect combustion of coal and
tarry substances, is also but slightly porous, brilliant, does
not soil or mark paper, is dense, almost devoid of the faculty
of retaining liquids and solids, and does not absorb gases. The
light sorts of charcoal produced from charred wood, on the other
hand, show this absorptive power in a most marked degree. This
property is particularly developed in that very fine and friable
charcoal prepared by heating animal substances such as hides and
bones. _The absorptive power of charcoal_ for gases is similar
to the condensation of gases in spongy platinum. Here evidently
there is a case of the adherence of gases to a solid, precisely
as liquids have the property of adhering to various solids. One
volume of charcoal will absorb the following volumes of gases
(charcoal is capable of absorbing an immense amount of chlorine,
almost equal to its own weight):--

--------------------------------------------------------
Saussure. Favre. Heat emitted
Boxwood Charcoal Cocoanut Charcoal per gram of gas
-------------------------------------------------------
NH_{3} 90 172 vols. 494 units
CO_{2} 35 97 " 158 "
N_{2}O 40 99 " 169 "
HCl 85 165 " 274 "
-------------------------------------------------------

The quantity of gas absorbed by the charcoal increases with the
pressure, and is approximately proportional to it. The quantity
of heat given out by the absorption nearly approaches that set
free on dissolving, or passing into a liquid condition.

Charcoal absorbs not only gases, but a number of other
substances. For instance, alcohol which contains disagreeably
smelling fusel oil, on being mixed with charcoal or filtered
through it, loses most of the fusel oil. The practice of
filtering substances through charcoal in order to get rid of
foreign matters is often applied in chemical and manufacturing
processes. Oils, spirits, various extracts, and vegetable and
other solutions are filtered through charcoal in order to purify
them. The bleaching power of charcoal may be tested by using
various coloured solutions--such as aniline dyes, litmus, &c.
Charcoal, which has absorbed one substance to saturation is still
capable of absorbing certain other substances. Animal charcoal,
produced in a very finely-divided state, especially by heating
bones, makes the best sort for the purposes of absorption. Bone
charcoal is used in large quantities in sugar works for filtering
syrups and all saccharine solutions, in order to purify them,
not only from colouring and odorous matter, but also from the
lime which is mixed with the syrups in order to render them
less unstable during boiling. The absorption of lime by animal
charcoal depends, in all probability, in a great degree on the
mineral component parts of bone charcoal.

[11] Charcoal is a very bad conductor of heat, and therefore forms an
excellent insulator or packing to prevent the transmission of
heat. A charcoal lining is often used in crucibles for heating
many substances, as it does not melt and resists a far greater
heat than many other substances.

[12] The unalterability of charcoal under the action of atmospheric
agencies, which produce changes in the majority of stony and
metallic substances, is often made use of in practice. For
example, charcoal is frequently strewn in boundary ditches. The
surface of wood is often charred to render it durable in those
places where the soil is damp and wood itself would soon rot. The
chambers (or in some works towers) through which acids pass (for
example, sulphuric and hydrochloric) in order to bring them into
contact with gases or liquids, are filled with charcoal or coke,
because at ordinary temperatures it resists the action of even
the strongest acids.

[12 bis] Maquenne (1892) discovered that carbon is capable of combining
with the alkali metals. A 20 p.c. amalgam of the metals was heated
to a red heat with charcoal powder in a stream of hydrogen. The
compounds so obtained possessed, after the mercury had been driven
off, the compositions BaC_{2}, SrC_{2}, CaC_{2}. All these
compounds react with water forming acetylene, for example:

BaC_{2} + 2H_{2}O = C_{2}H_{2} + Ba(OH)_{2}

Maquenne proposes the barium carbide as a source of acetylene. He
obtained this compound by heating carbonate of barium, magnesium
powder, and retort carbon in a Perreau furnace (BaCO_{3} + 3Mg + C
= 3MgO + BaC_{2}). One hundred grams of BaC_{2} evolve 5,200 to
5,400 c.c. of acetylene, mixed with about 2-3 p.c. of hydrogen.

The relation of acetylene, C_{2}H_{2}, to these metallic carbides
is evident from the fact that these metals (Ca, Sr, Ba) replace 2
atoms of hydrogen, and therefore C_{2}Ba corresponds to
C_{2}H_{2}, so that they may be regarded as metallic derivatives
of acetylene. Moissan (1893) obtained similar carbides directly
from the oxides by subjecting them to the action of the voltaic
arc, in the presence of carbon, for instance, BaO + 3C = CO +
C_{2}Ba, although at a furnace heat carbon has no action on the
oxides CaO, BaO, SrO. Concerning Al_{4}C_{5}, _see_ Chapter XVII.
Note 38.

[13] When subjected to pressure, charcoal loses heat, hence the densest
form stands to the less dense as a solid to a liquid, or as a
compound to an element. From this the conclusion may be drawn
that the molecules of graphite are more complex than those of
charcoal, and those of the diamond still more so. The specific
heat shows the same variation, and as we shall see further on,
the increased complexity of a molecule leads to a diminution of
the specific heat. At ordinary temperatures the specific heat of
charcoal is 0·24, graphite 0·20, the diamond 0·147. For retort
carbon Le Chatelier (1893) found that the product of the sp. heat
and atomic weight varies, between 0° and 250°, according to the
formula: = 1·92 + 0·0077_t_, and between 250° and 1000°, = 3·54 +
0·00246_t_ (_see_ Chapter XIV. Note 4).

By means of intense heat charcoal may be transformed into graphite. If a charcoal rod 4 mm. in diameter and 5 mm. long be enclosed in an exhausted receiver and the current from 600 Bunsen's elements, placed in parallel series of 100, be passed through it, the charcoal becomes strongly incandescent, partially volatilises, and is deposited in the form of graphite. If sugar be placed in a charcoal crucible and a powerful galvanic current passed through it, it is baked into a mass similar to graphite. If charcoal be mixed with wrought iron and heated, cast iron is formed, which contains as much as five per cent. of charcoal. If molten cast iron be suddenly chilled, the carbon remains in combination with the iron, forming so called white cast iron; but if the cooling proceeds slowly, the greater part of the carbon separates in the form of graphite, and if such cast iron (so called grey cast iron) be dissolved in acid, the carbon remains in the form of graphite. Graphite is met with in nature, sometimes in the form of large compact masses, sometimes permeating rocky formations like the schists or slates, and in fact is met with in those places which, in all probability, have been subjected to the action of subterranean heat.[14] The graphite in cast iron, and sometimes also natural graphite, occasionally appears in a crystalline form in the shape of six-sided plates, but more often it occurs as a compact amorphous mass having the characteristic properties of the familiar black-lead pencil.[15]

[14] There are places where anthracite gradually changes into graphite
as the strata sink. I myself had the opportunity of observing
this gradual transformation in the valley of Aosta.

[15] Pencils are made of graphite worked up into a homogeneous mass by
disintegrating, powdering, and cleansing it from earthy
impurities; the best kinds are made of completely homogeneous
graphite sawn up into the requisite sticks. Graphite is found in
many places. In Russia the so-called Aliberoffsky graphite is
particularly renowned; it is found in the Altai mountains near
the Chinese frontier; in many places in Finland and likewise
on the banks of the Little Tungouska, Sidoroff also found a
considerable quantity of graphite. When mixed with clay, graphite
is used for making crucibles and pots for melting metals.

Graphite, like most forms of charcoal, still contains a certain
quantity of hydrogen, oxygen, and ash, so that in its natural
state it does not contain more than 98 _p.c._ of carbon.

In practice, graphite is purified simply by washing it when in
a finely-ground state, by which means the bulk of the earthy
matter may be separated. The following process, proposed by
Brodie, consists in mixing the powdered graphite with 1/14 part
of its weight of potassium chlorate. The mixture is then heated
with twice its weight of strong sulphuric acid until no more
odoriferous gases are emitted; on cooling, the mixture is thrown
into water and washed; the graphite is then dried and heated
to a red heat; after this it shrinks considerably in volume
and forms a very fine powder, which is then washed. By acting
on graphite several times with a mixture of potassium chlorate
and nitric acid heated up to 60°, Brodie transformed it into a
yellow insoluble acid substance which he called graphitic acid,
C_{11}H_{4}O_{5}. The diamond remains unchanged when subjected to
this treatment, whilst amorphous charcoal is completely oxidised.
Availing himself of this possibility of distinguishing graphite
from the diamond or amorphous charcoal, Berthelot showed that
when compounds of carbon and hydrogen are decomposed by heat,
amorphous charcoal is mainly formed, whilst when compounds of
carbon with chlorine, sulphur, and boron are decomposed, graphite
is principally deposited.

The diamond is a crystalline and transparent form of carbon. It is of rare occurrence in nature, and is found in the alluvial deposits of the diamond mines of Brazil, India, South Africa, &c. It has also been found in meteorites.[15 bis] It crystallises in octahedra, dodecahedra, cubes, and other forms of the regular system.[16] The efforts which have been made to produce diamonds artificially, although they have not been fruitless, have not as yet led to the production of large-sized crystals, because those means by which crystals are generally formed are inapplicable to carbon. Indeed, carbon in all its forms being insoluble and infusible does not pass into a liquid condition by means of which crystallisation could take place. Diamonds have several times been successfully produced in the shape of minute crystals having the appearance of a black powder, but when viewed under the microscope appearing transparent, and possessing that hardness which is the peculiar characteristic of the diamond. This diamond powder is deposited on the negative electrode, when a weak galvanic current is passed through liquid chloride of carbon.[16 bis]

[15 bis] Diamonds are found in a particular dense rock, known by the
name of itacolumite, and are dug out of the _débris_ produced by
the destruction of the itacolumite by water. When the _débris_ is
washed the diamonds remain behind; they are principally found in
Brazil, in the provinces of Rio and Bahia, and at the Cape of Good
Hope. The _débris_ gives the black or amorphous diamond,
carbonado, and the ordinary colourless or yellow translucent
diamond. As the diamond possesses a very marked cleavage, the
first operation consists in splitting it, and then roughly and
finely polishing it with diamond powder. It is very remarkable
that Professors P. A. Latchinoff and Eroféeff found (1887) diamond
powder in a meteoric stone which fell in the Government of Penza,
in the district of Krasnoslobodsk, near the settlement of Novo
Urei (Sept. 10, 1886). Up to that time charcoal and graphite (a
special variety, cliftonite) had been found in meteorites and the
diamond only conjectured to occur therein. The Novo Urei meteorite
was composed of siliceous matter and metallic iron (with nickel)
like many other meteorites.

[16] Diamonds are sometimes found in the shape of small balls, and in
that case it is impossible to cut them because directly the
surface is ground or broken they fall into minute pieces.
Sometimes minute diamond crystals form a dense mass like sugar,
and this is generally reduced to diamond powder and used for
grinding. Some known varieties of the diamond are almost opaque
and of a black colour. Such diamonds are as hard as the ordinary
ones, and are used for polishing diamonds and other precious
stones, and also for rock boring and tunnelling.