Chapter VIII: Carbon and the Hydrocarbons (3)

Cases of isomerism in the restricted sense of the word--that is, when with an identity of composition and of molecular weight, the properties of the substances are different--are very numerous among the hydrocarbons and their derivatives. Such cases are particularly important for the comprehension of molecular structure and they also, like the polymerides, may be predicted from the above-mentioned conceptions, expressing the principles of the structure of the carbon compounds[42] based on the law of substitution. According to it, for example, it is evident that there can be no isomerism in the cases of the saturated hydrocarbons C_{2}H_{6} and C_{3}H_{8}, because the former is CH_{4}, in which methyl has taken the place of H, and as all the hydrogen atoms of methane must be supposed to have the same relation to the carbon, it is all the same which of them be subjected to the methyl substitution--the resulting product can only be ethane, CH_{3}CH_{3};[43] the same argument also applies in the case of propane, CH_{3}CH_{2}CH_{3}, where one compound only can be imagined. It is to be expected, however, that there should be two butanes, C_{4}H_{10}, and this is actually the case. In one, methyl may be considered as replacing the hydrogen of one of the methyls, CH_{3}CH_{2}CH_{2}CH_{3}; and in the other CH_{3} may be considered as substituted for H in /CH_{3} CH_{2}, and there it will consist of CH_{3}CH. The latter may \CH_{3} also be regarded as methane in which three of hydrogen are exchanged for three of methyl. On going further in the series it is evident that the number of possible isomerides will be still greater, but we have limited ourselves to the simplest examples, showing the possibility and actual existence of isomerides. C_{2}H_{4} and CH_{2}CH_{2} are, it is evident, identical; but there ought to be, and are, two hydrocarbons of the composition C_{3}H_{6}, propylene and trimethylene; the first is ethylene, CH_{2}CH_{2}, in which one atom of hydrogen is exchanged for methyl, CH_{2}CHCH_{3}, and trimethylene is ethane, CH_{3}CH_{3}, with the substitution of methylene for two hydrogen atoms from two methyl groups--that /CH_{2} is, CH_{2},[44] where the methylene introduced is united to both \CH_{2} the atoms of carbon in CH_{3}CH_{3}. It is evident that the cause of isomerism here is, on the one hand, the difference of the amount of hydrogen in union with the particular atoms of carbon, and, on the other, the different connection between the several atoms of carbon. In the first case they may be said to be chained together (more usually to form an 'open chain'), and in the second case, to be locked together (to form a 'closed chain' or 'ring'). Here also it is easily understood that on increasing the quantity of carbon atoms the number of possible and existing isomerides will greatly increase. If, at the same time, in addition to the substitution of one of the radicles of methane for hydrogen a further exchange of part of the hydrogen for some of the other groups of elements X, Y ... occurs, the quantity of possible isomerides still further increases in a considerable degree. For instance, there are even two possible isomerides for the derivatives of ethane, C_{2}H_{6}: if two atoms of the hydrogen be exchanged for X_{2}, one will have the ethylene structure, CH_{2}XCH_{2}X, and the other an ethylidene structure, CH_{3}CHX_{2}; such are, for instance, ethylene chloride, CH_{2}ClCH_{2}Cl, and ethylidene chloride, CH_{3}CHCl_{2}. And as in the place of the first atom of hydrogen not only metals may be substituted, but Cl, Br, I, OH (the water radicle), NH_{2} (the ammonia radicle), NO_{2} (the radicle of nitric acid), &c., so also in exchange for two atoms of hydrogen O, NH, S, &c., may be substituted; hence it will be understood that the quantity of isomerides is sometimes very great. It is impossible here to describe how the isomerides are distinguished from each other, in what reactions they occur, how and when one changes into another, &c.; for this, taken together with the description of the hydrocarbons already known, and their derivatives, forms a very extensive and very thoroughly investigated branch of chemistry, called _organic chemistry_. Enriched with a mass of closely observed phenomena and strictly deduced generalisations, this branch of chemistry has been treated separately for the reason that in it the hydrocarbon groups are subjected to transformations which are not met with in such quantity in dealing with any of the other elements or their hydrogen compounds. It was important for us to show that notwithstanding the great variety of the hydrocarbons and their products,[45] they are all of them governed by the law of substitution, and referring our readers for detailed information to works on organic chemistry, we will limit ourselves to a short exposition of the properties of the two simplest unsaturated hydrocarbons: ethylene, CH_{2}CH_{2}, and acetylene, CHCH, and a short acquaintance with petroleum as the natural source of a mass of hydrocarbons. _Ethylene, or olefiant gas_, C_{2}H_{4}, is the lowest known member of the unsaturated hydrocarbon series of the composition C_{_n_}H_{2_n_}. As in composition it is equal to two molecules of marsh gas deprived of two molecules of hydrogen, it is evident that it might be, and it actually can be, produced, although but in small quantities, together with hydrogen, by heating marsh gas. On being heated, however, olefiant gas splits up, first into acetylene and methane (3C_{2}H_{4} = 2C_{2}H_{2} + 2CH_{4}, Lewes, 1894), and at a higher temperature into carbon and hydrogen; and therefore in those cases where marsh gas is produced by heating, olefiant gas, hydrogen, and charcoal will also be formed, although only in small quantities. The lower the temperature at which complex organic substances are heated, the greater the quantity of olefiant gas found in the gases given off; at a white heat it is entirely decomposed into charcoal and marsh gas. If coal, wood, and more particularly petroleum, tars, and fatty substances, are subjected to dry distillation, they give off illuminating gas, which contains more or less olefiant gas.

[42] The conception of the structure of carbon compounds--that is, the
expression of those unions and correlations which their atoms
have in the molecules--was for a long time limited to the
representation that organic substances contained complex
radicles (for instance, ethyl C_{2}H_{5}, methyl CH_{3}, phenyl
C_{6}H_{5}, &c.); then about the year 1840 the phenomena
of substitution and the correspondence of the products of
substitution with the primary bodies (nuclei and types) were
observed, but it was not until about the year 1860 and later when
on the one hand the teaching of Gerhardt about molecules was
spreading, and on the other hand the materials had accumulated
for discussing the transformations of the simplest hydrocarbon
compounds, that conjectures began to appear as to the mutual
connection of the atoms of carbon in the molecules of the complex
hydrocarbon compounds. Then Kekulé and A. M. Butleroff began to
formulate the connection between the separate atoms of carbon,
regarding it as a quadrivalent element. Although in their
methods of expression and in some of their views they differ
from each other and also from the way in which the subject is
treated in this work, yet the essence of the matter--namely,
the comprehension of the causes of isomerism and of the union
between the separate atoms of carbon--remains the same. In
addition to this, starting from the year 1870, there appears a
tendency which from year to year increases to discover the actual
spacial distribution of the atoms in the molecules. Thanks to the
endeavours of Le-Bel (1874), Van't Hoff (1874), and Wislicenus
(1887) in observing cases of isomerism--such as the effect of
different isomerides on the direction of the rotation of the
plane of polarisation of light--this tendency promises much
for chemical mechanics, but the details of the still imperfect
knowledge in relation to this matter must be sought for in
special works devoted to organic chemistry.

[43] Direct experiment shows that however CH_{3}X is prepared (where
X = for instance Cl, &c.) it is always one and the same
substance. If, for example, in CX_{4}, X is gradually replaced by
hydrogen until CH_{3}X is produced, or in CH_{4}, the hydrogen by
various means is replaced by X, or else, for instance, if CH_{3}X
be obtained by the decomposition of more complex compounds, the
same product is always obtained.

This was shown in the year 1860, or thereabout, by many methods,
and is the fundamental conception of the structure of hydrocarbon
compounds. If the atoms of hydrogen in methyl were not absolutely
identical in value and position (as they are not, for instance,
in CH_{3}CH_{2}CH_{3} or CH_{3}CH_{2}X), then there would be as
many different forms of CH_{3}X as there were diversities in the
atoms of hydrogen in CH_{4}. The scope of this work does not
permit of a more detailed account of this matter. It is given in
works on organic chemistry.

[44] The union of carbon atoms in closed chains or rings was first
suggested by Kekulé as an explanation of the structure and
isomerism of the derivatives of benzene, C_{6}H_{6}, forming
aromatic compounds (Note 26).

[45] The following are the most generally known of the oxygenised but
non-nitrogenous hydrocarbon derivatives. (1) the alcohols. These
are hydrocarbons in which hydrogen is exchanged for hydroxyl
(OH). The simplest of these is methyl alcohol, CH_{3}(OH),
or wood spirit obtained by the dry distillation of wood. The
common spirits of wine or ethyl alcohol, C_{2}H_{3}(OH), and
glycol, C_{2}H_{4}(OH)_{2}, correspond with ethane. Normal
propyl alcohol, CH_{3}CH_{2}CH_{2}(OH), and isopropyl alcohol,
CH_{3}CH(OH)CH_{3}, propylene-glycol, C_{3}H_{6}(OH)_{2}, and
glycerol, C_{3}H_{3}(OH)_{3} (which, with stearic and other
acids, forms fatty substances), correspond with propane,
C_{3}H_{8}. All alcohols are capable of forming water and
ethereal salts with acids, just as alkalis form ordinary salts.
(2) Aldehydes are alcohols minus hydrogen; for instance,
acetaldehyde, C_{2}H_{4}O, corresponds with ethyl alcohol.
(3) It is simplest to regard organic acids as hydrocarbons in
which hydrogen has been exchanged for carboxyl (CO_{2}H), as
will be explained in the following chapter. There are a number
of intermediate compounds; for example, the aldehyde-alcohols,
alcohol-acids (or hydroxy-acids), &c. Thus the hydroxy-acids are
hydrocarbons in which some of the hydrogen has been replaced
by hydroxyl, and some by carboxyl; for instance, lactic
acid corresponds with C_{2}H_{6}, and has the constitution
C_{2}H_{4}(OH)(CO_{2}H). If to these products we add the haloid
salts (where H is replaced by Cl, Br, I), the nitro-compounds
containing NO_{2} in place of H, the amides, cyanides, ketones,
and other compounds, it will be readily seen what an immense
number of organic compounds there are and what a variety of
properties these substances have; this we see also from the
composition of plants and animals.

Olefiant gas, almost free from other gases,[46] may be obtained from ordinary alcohol (if possible, free from water) if it be mixed with five parts of strong sulphuric acid and the mixture heated to slightly above 100°. Under these conditions, the sulphuric acid removes the elements of water from the alcohol, C_{2}H_{5}(OH), and gives olefiant gas; C_{2}H_{6}O = H_{2}O + C_{2}H_{4}. The greater molecular weight of olefiant gas compared with marsh gas indicates that it may be comparatively easily converted into a liquid by means of pressure or great cold; this may be effected, for example, by the evaporation of liquid nitrous oxide. Its absolute boiling point is +10°, it boils at -103° (1 atmosphere), liquefies at 0°, at a pressure of 43 atmospheres, and solidifies at -160°. Ethylene is colourless, has a slight ethereal smell, is slightly soluble in water, and somewhat more soluble in alcohol and in ether (in five volumes of spirit and six volumes of ether).[47]

[46] Ethylene bromide, C_{2}H_{4}Br_{2}, when gently heated in
alcoholic solution with finely divided zinc, yields pure
ethylene, the zinc merely taking up the bromine (Sabaneyeff).

[47] Ethylene decomposes somewhat easily under the influence of the
electric spark, or a high temperature. In this case the volume
of the gas formed may remain the same when olefiant gas is
decomposed into carbon and marsh gas, or may increase to double
its volume when hydrogen and carbon are formed, C_{2}H_{4} =
CH_{4} + C = 2C + 2H_{2}. A mixture of olefiant gas and oxygen is
highly explosive; two volumes of this gas require six volumes of
oxygen for its perfect combustion. The eight volumes thus taken
then resolve themselves into eight volumes of the products of
combustion, a mixture of water and carbonic anhydride, C_{2}H_{4}
+ 3O_{2} = 2CO_{2} + 2H_{2}O. On cooling after the explosion
diminution of volume occurs because the water becomes liquid. For
two volumes of the olefiant gas taken, the diminution will be
equal to four volumes, and the same for marsh gas. The quantity
of carbonic anhydride formed by both gases is not the same. Two
volumes of marsh gas give only two volumes of carbonic anhydride,
and two volumes of ethylene give four volumes of carbonic
anhydride.

Like other unsaturated hydrocarbons, olefiant gas readily enters into combination with certain substances, such as chlorine, bromine, iodine, fuming sulphuric acid, or sulphuric anhydride, &c. If olefiant gas be sealed up with a small quantity of sulphuric acid in a glass vessel, and constantly agitated (as, for instance, by attaching it to the moving part of a machine), the prolonged contact and repeated mixing causes the olefiant gas, little by little, to combine with the sulphuric acid, forming C_{2}H_{4}H_{2}SO_{4}. If, after this absorption, the sulphuric acid be diluted with water and distilled, alcohol separates, which is produced in this case by the olefiant gas combining with the elements of water, C_{2}H_{4} + H_{2}O = C_{2}H_{6}O. In this reaction (Berthelot) we see an excellent example of the fact that if a given substance, like olefiant gas, is produced by the decomposition of another, then in the reverse way this substance, entering into combination, is capable of forming the original substance--in our example, alcohol. In combination with various molecules, X_{2}, ethylene gives saturated compounds, C_{2}H_{4}X_{2} or CH_{2}XCH_{2}X (for example, C_{2}H_{4}Cl_{2}), which correspond with ethane, CH_{3}CH_{3} or C_{2}H_{6}.[48]

[48] The homologues of ethylene, C_{_n_}H_{2_n_}, are also capable
of direct combination with halogens, &c., but with various
degrees of facility. The composition of these homologues can be
expressed thus: (CH_{3})__x_(CH_{2})_{_y_}(CH)_{_z_}C_{_r_},
where the sum of _x_ + _z_ is always an even number, and
the sum of _x_ + _z_ + _r_ is equal to half the sum of
3_x_ + _z_, whence _z_ + 2_r_ = _x_; by this means the possible
isomerides are determined. For example, for butylenes,
C_{4}H_{8}, (CH_{3})_{2}(CH)_{2}, (CH_{3})_{2}(CH_{2})C,
(CH_{2})(CH_{2})_{2}CH, and (CH_{2})_{4} are possible.

_Acetylene_, C_{2}H_{2} = CHCH, is a gas; it was first prepared by Berthelot (1857). It has a very pungent smell, is characterised by its great stability under the action of heat, and is obtained as the only product of the direct combination of carbon with hydrogen when a luminous arc (voltaic) is formed between carbon electrodes. This arc contains particles of carbon passing from one pole to the other. If the carbons be surrounded with an atmosphere of hydrogen, the carbon in part combines with the hydrogen, forming C_{2}H_{2}.[48 bis] Acetylene may be formed from olefiant gas if two atoms of hydrogen be taken from it. This may be effected in the following way: the olefiant gas is first made to combine with bromine, giving C_{2}H_{4}Br_{2}; from this the hydrobromic acid is removed by means of an alcoholic solution of caustic potash, leaving the volatile product C_{2}H_{3}Br; and from this yet another part of hydrobromic acid is withdrawn by passing it through anhydrous alcohol in which metallic sodium has been dissolved, or by heating it with a strong alcoholic solution of caustic potash. Under these circumstances (Berthelot, Sawitsch, Miasnikoff) the alkali takes up the hydrobromic acid from C_{_n_}H_{2_n_-1}Br, forming C_{_n_}H_{2_n_-2}.

[48 bis] _See_ also method of preparing C_{2}H_{2} in Note 12 bis.

Acetylene is also produced in all those cases where organic substances are decomposed by the action of a high temperature--for example, by dry distillation. On this account a certain quantity is always found in coal gas, and gives to it, at all events in part, its peculiar smell, but the quantity of acetylene in coal gas is very small. If the vapour of alcohol be passed through a heated tube a certain quantity of acetylene is formed. It is also produced by the imperfect combustion of olefiant and marsh gas--for example, if the flame of coal gas has not free access to air.[49] The inner part of every flame contains gases in imperfect combustion, and in them some amount of acetylene.

[49] This is easily accomplished with those gas burners which are used
in laboratories and mentioned in the Introduction. In these
burners the gas is first mixed with air in a long tube, above
which it is kindled. But if it be lighted inside the pipe it
does not burn completely, but forms acetylene, on account of
the cooling effect of the walls of the metallic tube; this is
detected by the smell, and may be shown by passing the issuing
gas (by aid of an aspirator) into an ammoniacal solution of
cuprous chloride.

Acetylene, being further removed than ethylene from the limit C_{_n_}H_{2_n_+2} of hydrocarbon compounds, has a still greater faculty of combination than is shown by olefiant gas, and therefore can be more readily separated from any mixture containing it. Actually, acetylene not only combines with one and two molecules of I_{2}, HI, H_{2}SO_{4}, Cl_{2}, Br_{2}, &c.... (many other unsaturated hydrocarbons combine with them), but also with cuprous chloride, CuCl, forming a red precipitate. If a gaseous mixture containing acetylene be passed through an ammoniacal solution of cuprous chloride (or silver nitrate), the other gases do not combine, but the acetylene gives a red precipitate (or grey with silver), which detonates when struck with a hammer. This red precipitate gives off acetylene under the action of acids. In this manner pure acetylene may be obtained. Acetylene and its homologues also readily react with corrosive sublimate, HgCl_{2} (Koucheroff, Favorsky). Acetylene burns with a very brilliant flame, which is accounted for by the comparatively large amount of carbon it contains.[50]

[50] Amongst the homologues of acetylene C_{_n_}H_{2_n_-2}, the lowest
is C_{3}H_{4}; allylene, CH_{3}CCH, and allene, CH_{2}CCH_{2},
are known, but the closed structure, CH_{2}(CH)_{2}, is little
investigated.

The formation and existence in nature of large masses of petroleum or a mixture of liquid hydrocarbons, principally of the series C_{_n_}H_{2_n_ +2} and C_{_n_}H_{2_n_} is in many respects remarkable.[51] In some mountainous districts--as, for instance, by the slopes of the Caucasian chain, on inclines lying in a direction parallel to the range--an oily liquid issues from the earth together with salt water and hot gases (methane and others); it has a tarry smell and dark brown colour, and is lighter than water. This liquid is called naphtha or rock oil (petroleum) and is obtained in large quantities by sinking wells and deep bore-holes in those places where traces of naphtha are observed, the naphtha being sometimes thrown up from the wells in fountains of considerable height.[52] The evolution of naphtha is always accompanied by salt water and marsh gas. Naphtha has from ancient times been worked in Russia in the Apsheron peninsula near Baku, and is also now worked in Burmah (India), in Galicia near the Carpathians, and in America, especially in Pennsylvania and Canada, &c. Naphtha does not consist of one definite hydrocarbon, but of a mixture of several, and its density, external appearance, and other qualities vary with the amount of the different hydrocarbons of which it is composed. The light kinds of naphtha have a specific gravity about 0·8 and the heavy kinds up to 0·98. The former are very mobile liquids, and more volatile; the latter contain less of the volatile hydrocarbons and are less mobile. When the light kinds of naphtha are distilled, the boiling point taken in the vapours constantly changes, beginning at 0° and going up to above 350°. That which passes over first is a very mobile, colourless ethereal liquid (forming gazolene, ligroin, benzoline, &c.), from which the hydrocarbons whose boiling points start from 0° may be extracted--namely, the hydrocarbons C_{4}H_{10}, C_{5}H_{12} (which boils at 30°), C_{6}H_{14} (boils at 62°), C_{7}H_{16} (boils about 90°), &c. Those fractions of the naphtha distillate which boil above 130°, and contain hydrocarbons with C_{9}, C_{10}, C_{11}, &c., enter into the composition of the oily substance, universally used for lighting, called kerosene or photogen or photonaphthalene, and by other names. The specific gravity of kerosene is from 0·78 to 0·84, and it smells like naphtha. Those products of the distillation of naphtha which pass off below 130° and have a specific gravity below 0·75, enter into the composition of light petroleum (benzoline, ligroin, petroleum spirit, &c.); which is used as a solvent for india-rubber, for removing grease spots, &c. Those portions of naphtha (which can only be distilled without change by means of superheated steam, otherwise they are largely decomposed) which boil above 275° and up to 300° and have a specific gravity higher than 0·85, form an excellent oil,[53] safe as regards inflammability (which is very important as diminishing the risks of fire), and may be used in lamps as an effective substitute for kerosene.[54] Those portions of naphtha which pass over at a still higher temperature and have a higher specific gravity than 0·9, which are found in abundance (about 30 p.c.) in the Baku naphtha, make excellent lubricating or machine oils. Naphtha has many important applications, and the naphtha industry is now of great commercial importance, especially as naphtha and its refuse may be used as fuel.[55] Whether naphtha was formed from organic matter is very doubtful, as it is found in the most ancient Silurian strata which correspond with epochs of the earth's existence when there was little organic matter; it could not penetrate from the higher to the lower (more ancient) strata as it floats on water (and water penetrates through all strata). It therefore tends to rise to the surface of the earth, and it is always found in highlands parallel to the direction of the mountains.[56] Much more probably its formation may be attributed to the action of water penetrating through the crevasses formed on the mountain slopes and reaching to the heart of the earth, to that kernel of heated metallic matter which must be accepted as existing in the interior of the earth. And as meteoric iron often contains carbon (like cast iron), so, accepting the existence of such carburetted iron at unattainable depths in the interior of the earth, it may be supposed that naphtha was produced by the action of water penetrating through the crevices of the strata during the upheaval of mountain chains,[57] because water with iron carbide ought to give iron oxide and hydrocarbons.[58] Direct experiment proves that the so-called _spiegeleisen_ (manganiferous iron, rich in chemically combined carbon) when treated with acids gives liquid hydrocarbons[59] which in composition, appearance, and properties are completely identical with naphtha.[60]

[51] The saturated hydrocarbons predominate in American petroleum,
especially in its more volatile parts; in Baku naphtha the
hydrocarbons of the composition C_{_n_}H_{2_n_} form the
main part (Lisenko, Markovnikoff, Beilstein) but doubtless
(Mendeléeff) it also contains saturated ones, C_{_n_}H_{2_n_+2}.
The structure of the naphtha hydrocarbons is only known for
the lower homologues, but doubtless the distinction between the
hydrocarbons of the Pennsylvanian and Baku naphthas, boiling at
the same temperature (after the requisite refining by repeated
fractional distillation, which can be very conveniently done
by means of steam rectification--that is, by passing the steam
through the dense mass), depends not only on the predominance
of saturated hydrocarbons in the former, and naphthenes,
C_{_n_}H_{2_n_}, in the latter, but also on the diversity of
composition and structure of the corresponding portions of the
distillation. The products of the Baku naphtha are richer in
carbon (therefore in a suitably constructed lamp they ought to
give a brighter light), they are of greater specific gravity, and
have greater internal friction (and are therefore more suitable
for lubricating machinery) than the American products collected
at the same temperature.

[52] The formation of naphtha fountains (which burst forth after the
higher clay strata covering the layers of sands impregnated
with naphtha have been bored through) is without doubt caused
by the pressure or tension of the combustible hydrocarbon
gases which accompany the naphtha, and are soluble in it under
pressure. Sometimes these naphtha fountains reach a height of 100
metres--for instance, the fountain of 1887 near Baku. Naphtha
fountains generally act periodically and their force diminishes
with the lapse of time, which might be expected, because the
gases which cause the fountains find an outlet, as the naphtha
issuing from the bore-hole carries away the sand which was
partially choking it up.

[53] This is a so-called intermediate oil (between kerosene and
lubricating oils), solar oil, or pyronaphtha. Lamps are already
being manufactured for burning it but still require improvement.
Above all, however, it requires a more extended market, and
this at present is wanting, owing to the two following reasons:
(1) Those products of the American petroleum which are the
most widely spread and almost universally consumed contain but
little of this intermediate oil, and what there is is divided
between the kerosene and the lubricating oils; (2) the Baku
naphtha, which is capable of yielding a great deal (up to 30
p.c.) of intermediate oil, is produced in enormous quantities,
about 300 million poods, but has no regular markets abroad,
and for the consumption in Russia (about 25 million poods of
kerosene per annum) and for the limited export (60 million
poods per annum) into Western Europe (by the Trans-Caucasian
Railway) those volatile and more dangerous parts of the naphtha
which enter into the composition of the American petroleum are
sufficient, although Baku naphtha yields about 25 p.c. of such
kerosene. For this reason pyronaphtha is not manufactured in
sufficient quantities, and the whole world is consuming the
unsafe kerosene. When a pipe line has been laid from Baku to the
Black Sea (in America there are many which carry the raw naphtha
to the sea-shore, where it is made into kerosene and other
products) then the whole mass of the Baku naphtha will furnish
safe illuminating oils, which without doubt will find an immense
application. A mixture of the intermediate oil with kerosene
or Baku oil (specific gravity 0·84 to 0·85) may be considered
(on removing the benzoline) to be the best illuminating oil,
because it is safe (flashing point from 40° to 60°), cheaper
(Baku naphtha gives as much as 60 p.c. of Baku oil), and burns
perfectly well in lamps differing but little from those made for
burning American kerosene (unsafe, flashing point 20° to 30°).

[54] The substitution of Baku pyronaphtha, or intermediate oil, or Baku
oil (_see_ Note 53), would not only be a great advantage as
regards safety from fire, but would also be highly economical.
A ton (62 poods) of American crude petroleum costs at the coast
considerably more than 24_s._ (12 roubles), and yields two-thirds
of a ton of kerosene suitable for ordinary lamps. A ton of raw
naphtha in Baku costs less than 4_s._ (1 rouble 80 copecks), and
with a pipe line to the shore of the Black Sea would not cost
more than 8 roubles, or 16_s._ Moreover, a ton of Baku naphtha
will yield as much as two-thirds of a ton of kerosene, Baku oil,
and pyronaphtha suitable for illuminating purposes.

[55] Naphtha has been applied for heating purposes on a large scale
in Russia, not only on account of the low cost of naphtha itself
and of the residue from the preparation of kerosene, but also
because the products of all the Baku naphtha do not find an
outlet for general consumption. Naphtha itself and its various
residues form excellent fuel, burning without smoke and giving
a high temperature (steel and iron may be easily melted in the
flame). A hundred poods of good coal (for instance, Don coal)
used as fuel for heating boilers are equivalent to 36 cubic feet
(about 250 poods) of dry wood, while only 70 poods of naphtha
will be required; and moreover there is no need for stoking, as
the liquid can be readily and evenly supplied in the required
quantity. The economic and other questions relating to American
and Baku petroleums have been discussed more in detail in some
separate works of mine (D. Mendeléeff): (1) 'The Naphtha Industry
of Pennsylvania and the Caucasus,' 1870; (2) 'Where to Build
Naphtha Works,' 1880; (3) 'On the Naphtha Question,' 1883; (4)
'The Baku Naphtha Question,' 1886; (5) the article on the naphtha
industry in the account of the Russian industries printed for the
Chicago Exhibition.

[56] As during the process of the dry distillation of wood, sea-weed,
and similar vegetable _débris_, and also when fats are decomposed
by the action of heat (in closed vessels), hydrocarbons similar
to those of naphtha are formed, it was natural that this fact
should have been turned to account to explain the formation
of the latter. But the hypothesis of the formation of naphtha
from vegetable _débris_ inevitably assumes coal to be the chief
element of decomposition, and naphtha is met with in Pennsylvania
and Canada, in the Silurian and Devonian strata, which do not
contain coal, and correspond to an epoch not abounding in organic
matter. Coal was formed from the vegetable _débris_ of the
Carboniferous, Jurassic, and other recent strata, but judging
more from its composition and structure, it has been subjected
to the same kind of decomposition as peat; nor could liquid
hydrocarbons have been thus formed to such an extent as we see
in naphtha. If we ascribe the derivation of naphtha to the
decomposition of fat (adipose, animal fat) we encounter three
almost insuperable difficulties: (1) Animal remains would furnish
a great deal of nitrogenous matter, whilst there is but very
little in naphtha; (2) the enormous quantity of naphtha already
discovered as compared with the insignificant amount of fat in
the animal carcase; (3) the sources of naphtha always running
parallel to mountain chains is completely inexplicable. Being
struck with this last-mentioned circumstance in Pennsylvania,
and finding that the sources in the Caucasus surround the whole
Caucasian range (Baku, Tiflis, Gouria, Kouban, Tamman, Groznoe,
Dagestan), I developed in 1876 the hypothesis of the mineral
origin of naphtha expounded further on.

[57] During the upheaval of mountain ranges crevasses would be formed
at the peaks with openings upwards, and at the foot of the
mountains with openings downwards. These cracks in course of time
fill up, but the younger the mountains the fresher the cracks
(the Alleghany mountains are, without doubt, more ancient than
the Caucasian, which were formed during the tertiary epoch);
through them water must gain access deep into the recesses of the
earth to an extent that could not occur on the level (on plains).
The situation of naphtha at the foot of mountain chains is the
principal argument in my hypothesis.

Another fundamental reason is the consideration of the mean
density of the earth. Cavendish, Airy, Cornu, Boys, and many
others who have investigated the subject by various methods,
found that, taking water = 1, the mean density of the earth
is nearly 5·5. As at the surface water and all rocks (sand,
clay, limestone, granite, &c.) have a density less than 3, it
is evident (as solid substances are but slightly compressible
even under the greatest pressure) that inside the earth there
are substances of a greater density--indeed, not less than 7
or 8. What conclusion, then, can be arrived at? Anything heavy
contained in the bosom of the earth must be distributed not
only on its surface, but throughout the whole solar system, for
everything tends to show that the sun and planets are formed from
the same material, and according to the hypothesis of Laplace
and Kant it is most probable, and indeed must necessarily be
held, that the earth and planets are but fragments of the solar
atmosphere, which have had time to cool considerably and become
masses semi-liquid inside and solid outside, forming both planets
and satellites. The sun amongst other heavy elements contains
a great deal of iron, as shown by spectrum analysis. There is
also much of it in an oxidised condition on the surface of the
earth. Meteoric stones, carried as fragmentary planets in the
solar system and sometimes falling upon the earth, consisting of
siliceous rocks similar to terrestrial ones, often contain either
dense masses of iron (for example, the Pallosovo iron preserved
in the St. Petersburg Academy of Sciences) or granular masses
(for instance, the Okhansk meteorite of 1886). It is therefore
possible that the interior of the earth contains much iron in a
metallic state. This might be anticipated from the hypothesis of
Laplace, for the iron must have been compressed into a liquid
at that period when the other component parts of the earth
were still strongly heated, and oxides of iron could not then
have been formed. The iron was covered with slags (mixtures of
silicates like glass fused with rocky matter) which did not allow
it to burn at the expense of the oxygen of the atmosphere or
of water, just at that time when the temperature of the earth
was very high. Carbon was in the same state; its oxides were
also capable of dissociation (Deville); it is also but slightly
volatile, and has an affinity for iron, and iron carbide is found
in meteoric stones (as well as carbon and even the diamond). Thus
the supposition of the existence of iron carbides in the interior
of the earth was derived by me from many indications, which
are to some extent confirmed by the fact that granular pieces
of iron have been found in some basalts (ancient lava) as well
as in meteoric stones. The occurrence of iron in contact with
carbon during the formation of the earth is all the more probable
because those elements predominate in nature which have small
atomic weights, and among them the most widely diffused, the most
difficultly fusible, and therefore the most easily condensed
(Chapter XV.) are carbon and iron. They passed into the liquid
state when all compounds were at a temperature of dissociation.

[58] The following is the typical equation for this formation:

3Fe_{_m_}C_{_n_} + 4_{_m_}H_{2}O = _m_Fe_{3}O_{4} (magnetic
oxide) + C_{5_n_}H_{8_m_} (_see_ Chapter XVII., Note 38).

[59] Cloez investigated the hydrocarbons formed when cast-iron is
dissolved in hydrochloric acid, and found C_{_n_}H_{2_n_} and
others. I treated crystalline manganiferous cast-iron with the
same acid, and obtained a liquid mixture of hydrocarbons exactly
similar to natural naphtha in taste, smell, and reaction.

[60] Probably naphtha was produced during the upheaval of all mountain
chains, but only in some cases were the conditions favourable
to its being preserved underground. The water penetrating below
formed there a mixture of naphtha and watery vapours, and this
mixture issued through fissures to the cold parts of the earth's
crust. The naphtha vapours, on condensing, formed naphtha,
which, if there were no obstacles, appeared on the surface
of land and water. Here part of it soaked through formations
(possibly the bituminous slates, schists, dolomites, &c., were
thus formed), another part was carried away on the water,
became oxidised, evaporated, and was driven to the shores (the
Caucasian naphtha probably in this way, during the existence of
the Aralo-Caspian sea, was carried as far as the Sisran banks
of the Volga, where many strata are impregnated with naphtha
and products of its oxidation resembling asphalt and pitch); a
great part of it was burnt in one way or another--that is, gave
carbonic anhydride and water. If the mixture of vapours, water,
and naphtha formed inside the earth had no free outlet to the
surface, it nevertheless would find its way through fissures to
the superior and colder strata, and there become condensed. Some
of the formations (clays) which do not absorb naphtha were only
washed away by the warm water, and formed mud, which we also now
observe issuing from the earth in the form of mud volcanoes. The
neighbourhood of Baku and the whole of the Caucasus near the
naphtha districts are full of such volcanoes, which from time to
time are in a state of eruption. In old naphtha beds (such as
the Pennsylvanian) even these blow-holes are closed, and the mud
volcanoes have had time to be washed away. The naphtha and the
gaseous hydrocarbons formed with it under the pressure of the
overlying earth and water impregnated the layers of sand, which
are capable of absorbing a great quantity of such liquid, and
if above this there were strata impermeable to naphtha (dense,
clayey, damp strata) the naphtha would accumulate in them. It is
thus preserved from remote geological periods up to the present
day, compressed and dissolved under the pressure of the gases
which burst out in places forming naphtha fountains. If this
be granted, it may be thought that in the comparatively new
(geologically speaking) mountain chains, such as the Caucasian,
naphtha is even now being formed. Such a supposition may explain
the remarkable fact that, in Pennsylvania, localities where
naphtha had been rapidly worked for five years have become
exhausted, and it becomes necessary to constantly have recourse
to sinking new wells in fresh places. Thus, from the year 1859,
the workings were gradually transferred along a line running
parallel to the Alleghany mountains for a distance of more
than 200 miles, whilst in Baku the industry dates from time
immemorial (the Persians worked near the village of Ballaghana)
and up to the present time keeps to one and the same place.
The amounts of the Pennsylvanian and Baku annual outputs are
at present equal--namely, about 250 million poods (4 million
tons). It may be that the Baku beds, as being of more recent
geological formation, are not so exhausted by nature as those of
Pennsylvania, and perhaps in the neighbourhood of Baku naphtha
is still being formed, which is partially indicated by the
continued activity of the mud volcanoes. As many varieties of
naphtha contain in solution solid slightly volatile hydrocarbons
like paraffin and mineral wax, the production of ozocerite,
or mountain wax, is accounted for in conjunction with the
formation of naphtha. Ozocerite is found in Galicia, also in
the neighbourhood of Novorossisk, in the Caucasus, and on the
islands of the Caspian Sea (particularly in the Chileken and Holy
Islands); it is met with in large masses, and is used for the
production of paraffin and _ceresene_, for the manufacture of
candles, and similar purposes.

As the naphtha treasures of the Caucasus have hardly been
exploited (near Baku and near Kouban and Grosnyi), and as naphtha
finds numerous uses, the subject presents most interesting
features to chemists and geologists, and is worthy of the close
attention of practical men.