HOW GAS IS MADE--ILLUMINATING OILS AND BYE-PRODUCTS.
Accustomed as we are at the present day to see street after street of
well-lighted thoroughfares, brilliantly illuminated by gas-lamps
maintained by public authority, we can scarcely appreciate the fact that
the use of gas is, comparatively speaking, of but recent growth, and
that, like the use of coal itself, it has not yet existed a century in
public favour. Valuable as coal is in very many different ways, perhaps
next in value to its actual use as fuel, ranks the use of the immediate
product of its distillation--viz., gas; and although gas is in some
respects waning before the march of the electric light in our day, yet,
even as gas at no time has altogether superseded old-fashioned oil, so we
need not anticipate a time when gas in turn will be likely to be
superseded by the electric light, there being many uses to which the one
may be put, to which the latter would be altogether inapplicable; for, in
the words of Dr Siemens, assuming the cost of electric light to be
practically the same as gas, the preference for one or other would in
each application be decided upon grounds of relative convenience, but
gas-lighting would hold its own as the poor man's friend. Gas is an
institution of the utmost value to the artisan; it requires hardly any
attention, is supplied upon regulated terms, and gives, with what should
be a cheerful light, a genial warmth, which often saves the lighting of a
fire.
The revolution which gas has made in the appearance of the streets, where
formerly the only illumination was that provided by each householder,
who, according to his means, hung out a more or less efficient lantern,
and consequently a more or less smoky one, cannot fail also to have
brought about a revolution in the social aspects of the streets, and
therefore is worthy to be ranked as a social reforming agent; and some
slight knowledge of the process of its manufacture, such as it is here
proposed to give, should be in the possession of every educated
individual. Yet the subjects which must be dealt with in this chapter are
so numerous and of such general interest, that we shall be unable to
enter more than superficially into any one part of the whole, but shall
strive to give a clear and comprehensive view, which shall satisfy the
inquirer who is not a specialist.
The credit of the first attempt at utilising the gaseous product of coal
for illumination appears to be due to Murdock, an engineer at Redruth,
who, in 1792, introduced it into his house and offices, and who, ten
years afterwards, as the result of numerous experiments which he made
with a view to its utilisation, made a public display at Birmingham on
the occasion of the Peace of Amiens, in 1802.
More than a century before, however, the gas obtained from coal had been
experimented upon by a Dr Clayton, who, about 1690, conceived the idea of
heating coal until its gaseous constituents were forced out of it. He
described how he obtained steam first of all, then a black oil, and
finally a "spirit," as our ancestors were wont to term the gas. This, to
his surprise, ignited on a light being applied to it, and he considerably
amused his friends with the wonders of this inflammatory spirit. For a
century afterwards it remained in its early condition, a chemical wonder,
a thing to be amused with; but it required the true genius and energy of
Murdock to show the great things of which it was capable.
London received its first instalment of gas in 1807, and during the next
few years its use became more and more extended, houses and streets
rapidly receiving supplies in quick succession. It was not, however, till
about the year 1820 that its use throughout the country became at all
general, St James' Park being gas-lit in the succeeding year. This is not
yet eighty years ago, and amongst the many wonderful things which have
sprung up during the present century, perhaps we may place in the
foremost rank for actual utility, the gas extracted from coal, conveyed
as it is through miles upon miles of underground pipes into the very
homes of the people, and constituting now almost as much a necessity of a
comfortable existence as water itself.
The use of gas thus rapidly extended for illuminating purposes, and to a
very great extent superseded the old-fashioned means of illumination.
[Illustration: FIG. 34.--Inside a Gas-Holder.]
The gas companies which sprang up were not slow to notice that, seeing
the gas was supplied by meter, it was to their pecuniary advantage "to
give merely the prescribed illuminating power, and to discourage the
invention of economical burners, in order that the consumption might
reach a maximum. The application of gas for heating purposes had not been
encouraged, and was still made difficult in consequence of the
objectionable practice of reducing the pressure in the mains during
daytime to the lowest possible point consistent with prevention of
atmospheric indraught."
The introduction of an important rival into the field in the shape of the
electric light has now given a powerful impetus to the invention and
introduction of effective gas-lamps, and amongst inventors of recent
years no name is, perhaps, in this respect so well known as the name of
Sugg. As long as gas retained almost the monopoly, there was no incentive
to the gas companies to produce an effective light cheaply; but now that
the question of the relative cheapness of gas and electricity is being
actively discussed, the gas companies, true to the instinct of
self-preservation, seem determined to show what can be done when gas is
consumed in a scientific manner.
In order to understand how best a burner should be constructed in order
that the gas that is burnt should give the greatest possible amount of
illumination, let us consider for a moment the composition of the gas
flame. It consists of three parts, (1) an interior dark space, in which
the elements of the gas are in an unconsumed state; (2) an inner ring
around the former, whence the greatest amount of light is obtained, and
in which are numerous particles of carbon at a white heat, each awaiting
a supply of oxygen in order to bring about combustion; and (3) an outer
ring of blue flame in which complete combustion has taken place, and from
which the largest amount of heat is evolved.
The second of these portions of the flame corresponds with the "reducing"
flame of the blow-pipe, since this part, if turned upon an oxide, will
reduce it, i.e., abstract its oxygen from it. This part also corresponds
with the jet of the Bunsen burner, when the holes are closed by which
otherwise air would mingle with the gas, or with the flame from a
gas-stove when the gas ignites beneath the proper igniting-jets, and
which gives consequently a white or yellow flame.
The third portion, on the other hand, corresponds with the "oxidising"
flame of the blow-pipe, since it gives up oxygen to bodies that are
thirsting for it. This also corresponds with the ordinary blue flame of
the Bunsen burner, and with the blue flame of gas-stoves where heat, and
not light, is required, the blue flame in both cases being caused by the
admixture of air with the gas.
Thus, in order that gas may give the best illumination, we must increase
the yellow or white space of carbon particles at a white heat, and a
burner that will do this, and at the same time hold the balance so that
unconsumed particles of carbon shall not escape in the way of smoke, will
give the most successful illuminating results. With this end in view the
addition of albo-carbon to a bulb in the gas-pipe has proved very
successful, and the incandescent gas-jet is constructed on exactly the
same chemical principle. The invention of burners which brought about
this desirable end has doubtless not been without effect in acting as a
powerful obstacle to the widespread introduction of the electric light.
Without entering into details of the manufacture of gas, it will be as
well just to glance at the principal parts of the apparatus used.
The gasometer, as it has erroneously been called, is a familiar object to
most people, not only to sight but unfortunately also to the organs of
smell. It is in reality of course only the gas-holder, in which the final
product of distillation of the coal is stored, and from which the gas
immediately passes into the distributing mains.
The first, and perhaps, most important portion of the apparatus used in
gas-making is the series of _retorts_ into which the coal is placed, and
from which, by the application of heat, the various volatile products
distil over. These retorts are huge cast-iron vessels, encased in strong
brick-work, usually five in a group, and beneath which a large furnace is
kept going until the process is complete. Each retort has an iron exit
pipe affixed to it, through which the gases generated by the furnace are
carried off. The exit pipes all empty themselves into what is known as
the _hydraulic main_, a long horizontal cylinder, and in this the gas
begins to deposit a portion of its impurities. The immediate products of
distillation are, after steam and air, gas, tar, ammoniacal liquor,
sulphur in various forms, and coke, the last being left behind in the
retort. In the hydraulic main some of the tar and ammoniacal liquor
already begin to be deposited. The gas passes on to the _condenser_,
which consists of a number of U-shaped pipes. Here the impurities are
still further condensed out, and are collected in the _tar-pit_ whilst
the gas proceeds, still further lightened of its impurities. It may be
mentioned that the temperature of the gas in the condenser is reduced to
about 60° F., but below this some of the most valuable of the illuminants
of coal-gas would commence to be deposited in liquid form, and care has
to be taken to prevent a greater lowering of temperature. A mechanical
contrivance known as the _exhauster_ is next used, by which the gas is,
amongst other things, helped forward in its onward movement through the
apparatus. The gas then passes to the _washers_ or _scrubbers_, a series
of tall towers, from which water is allowed to fall as a fine spray, and
by means of which large quantities of ammonia, sulphuretted hydrogen,
carbonic acid and oxide, and cyanogen compounds, are removed. In the
scrubber the water used in keeping the coke, with which it is filled,
damp, absorbs these compounds, and the union of the ammonia with certain
of them takes place, resulting in the formation of carbonate of ammonia
(smelling salts), sulphide and sulphocyanide of ammonia.
[Illustration: FIG. 35.--Filling Retorts by Machinery.]
[Illustration: FIG. 36.--CONDENSERS.]
Hitherto the purification of the gas has been brought about by mechanical
means, but the gas now enters the "_purifier_," in which it undergoes a
further cleansing, but this time by chemical means.
[Illustration: FIG. 37.]
The agent used is either lime or hydrated oxide of iron, and by their
means the gas is robbed of its carbonic acid and the greater part of its
sulphur compounds. The process is then considered complete, and the gas
passes on into the water chamber over which the gas-holder is reared, and
in which it rises through the water, forcing the huge cylinder upward
according to the pressure it exerts.
The gas-holder is poised between a number of upright pillars by a series
of chains and pulleys, which allow of its easy ascent or descent
according as the supply is greater or less than that drawn from it by the
gas mains.
[Illustration: FIG. 38.]
When we see the process which is necessary in order to obtain pure gas,
we begin to appreciate to what an extent the atmosphere is fouled when
many of the products of distillation, which, as far as the production of
gas is concerned, may be called impurities, are allowed to escape free
without let or hindrance. In these days of strict sanitary inspection it
seems strange that the air in the neighbourhood of gas-works is still
allowed to become contaminated by the escape of impure compounds from the
various portions of the gas-making apparatus. Go where one may, the
presence of these compounds is at once apparent to the nostrils within a
none too limited area around them, and yet their deleterious effects can
be almost reduced to a minimum by the use of proper purifying agents, and
by a scientific oversight of the whole apparatus. It certainly behoves
all sanitary authorities to look well after any gas-works situated within
their districts.
Now let us see what these first five products of distillation actually
are.
Firstly, house-gas. Everybody knows what house-gas is. It cannot,
however, be stated to be any one gas in particular, since it is a
mechanical mixture of at least three different gases, and often contains
small quantities of others.
A very large proportion consists of what is known as marsh-gas, or light
carburetted hydrogen. This occurs occluded or locked up in the pores of
the coal, and often oozes out into the galleries of coal-mines, where it
is known as firedamp (German _dampf_, vapour). It is disengaged wherever
vegetable matter has fallen and has become decayed. If it were thence
collected, together with an admixture of ten times its volume of air, a
miniature coal-mine explosion could be produced by the introduction of a
match into the mixture. Alone, however, it burns with a feebly luminous
flame, although to its presence our house-gas owes a great portion of its
heating power. Marsh-gas is the first of the series of hydro-carbons
known chemically as the _paraffins_, and is an extremely light substance,
being little more than half the weight of an equal bulk of air. It is
composed of four atoms of hydrogen to one of carbon (CH_{4}).
Marsh-gas, together with hydrogen and the monoxide of carbon, the last of
which burns with the dull blue flame often seen at the surface of fires,
particularly coke and charcoal fires, form about 87 per cent. of the
whole volume of house-gas, and are none of them anything but poor
illuminants.
The illuminating power of house-gas depends on the presence therein of
olefiant gas (_ethylene_), or, as it is sometimes termed, heavy
carburetted hydrogen. This is the first of the series of hydro-carbons
known as the _olefines_, and is composed of two atoms of carbon to every
four atoms of hydrogen (C_{2}H_{4}). Others of the olefines are present
in minute quantities. These assist in increasing the illuminosity, which
is sometimes greatly enhanced, too, by the presence of a small quantity
of benzene vapour. These illuminants, however, constitute but about 6 per
cent. of the whole.
Added to these, there are four other usual constituents which in no way
increase the value of gas, but which rather detract from it. They are
consequently as far as possible removed as impurities in the process of
gas-making. These are nitrogen, carbonic acid gas, and the destructive
sulphur compounds, sulphuretted hydrogen and carbon bisulphide vapour. It
is to the last two to which are to be attributed the injurious effects
which the burning of gas has upon pictures, books, and also the
tarnishing which metal fittings suffer where gas is burnt, since they
give rise to the formation of oil of vitriol (sulphuric acid), which is
being incessantly poured into the air. Of course the amount so given off
is little as compared with that which escapes from a coal fire, but,
fortunately for the inmates of the room, in this case the greater
quantity goes up the chimney; this, however, is but a method of
postponing the evil day, until the atmosphere becomes so laden with
impurities that what proceeds at first up the chimney will finally again
make its way back through the doors and windows. A recent official report
tells us that, in the town, of St Helen's alone, sufficient sulphur
escapes annually into the atmosphere to finally produce 110,580 tons of
sulphuric acid, and a computation has been made that every square mile of
land in London is deluged annually with 180 tons of the same
vegetation-denuding acid. It is a matter for wonder that any green thing
continues to exist in such places at all.
The chief constituents of coal-gas are, therefore, briefly as
follows:--
/ (1) Hydrogen,
| (2) Marsh-gas (carburetted hydrogen or fire-damp),
| (3) Carbon monoxide,
| (4) Olefiant gas (ethylene, or heavy carburetted hydrogen), with
\ other olefines,
/ (5) Nitrogen,
| (6) Carbonic acid gas,
| (7) Sulphuretted hydrogen,
\ (8) Carbon bisulphide (vapour),
the last four being regarded as impurities, which are removed as far as
possible in the manufacture.
In the process of distillation of the coal, we have seen that various
other important substances are brought into existence. The final residue
of coke, which is impregnated with the sulphur which has not been
volatilised in the form of sulphurous gases, we need scarcely more than
mention here. But the gas-tar and the ammoniacal liquor are two important
products which demand something more than our casual attention. At one
time regarded by gas engineers as unfortunately necessary nuisances in
the manufacture of gas, they have both become so valuable on account of
materials which can be obtained from them, that they enable gas itself to
be sold now at less than half its original price. The waste of former
generations is being utilised in this, and an instance is recorded in
which tar, which was known to have been lying useless at the bottom of a
canal for years, has been purchased by a gas engineer for distilling
purposes. It has been estimated that about 590,000 tons of coal-tar are
distilled annually.
Tar in its primitive condition has been used, as every one is aware, for
painting or tarring a variety of objects, such as barges and palings, in
fact, as a kind of protection to the object covered from the ravages of
insects or worms, or to prevent corrosion when applied to metal piers.
But it is worthy of a better purpose, and is capable of yielding far more
useful and interesting substances than even the most imaginative
individual could have dreamed of fifty years ago.
In the process of distillation, the tar, after standing in tanks for some
time, in order that any ammoniacal liquor which may be present may rise
to the surface and be drawn off, is pumped into large stills, where a
moderate amount of heat is applied to it. The result is that some of the
more volatile products pass over and are collected in a receiver. These
first products are known as _first light oils_, or _crude coal-naphtha_,
and to this naphtha all the numerous natural naphthas which have been
discovered in various portions of the world, and to which have been
applied numerous local names, bear a very close resemblance. Such an one,
for instance, was that small but famous spring at Biddings, in
Derbyshire, from which the late Mr Young--Paraffin Young--obtained his
well-known paraffin oil, which gave the initial impetus to what has since
developed into a trade of immense proportions in every quarter of the
globe.
After a time the crude coal-naphtha ceases to flow over, and the heat is
increased. The result is that a fresh series of products, known as
_medium oils_, passes over, and these oils are again collected and kept
separate from the previous series. These in turn cease to flow, when, by
a further increase of heat, what are known as the _heavy oils_ finally
pass over, and when the last of these, _green grease_, as it is called,
distils over, pitch alone is left in the still. Pitch is used to a large
extent in the preparation of artificial asphalte, and also of a fuel
known as "briquettes."
The products thus obtained at the various stages of the process are
themselves subjected to further distillation, and by the exercise of
great care, requiring the most delicate and accurate treatment, a large
variety of oils is obtained, and these are retailed under many and
various fanciful names.
One of the most important and best known products of the fractional
distillation of crude coal-naphtha is that known as _benzene_, or
benzole, (C_{6}H_{6}). This, in its unrefined condition, is a light
spirit which distils over at a point somewhat below the boiling point of
water, but a delicate process of rectification is necessary to produce
the pure spirit. Other products of the same light oils are toluene and
xylene.
Benzene of a certain quality is of course a very familiar and useful
household supplement. It is sometimes known and sold as _benzene collas_,
and is used for removing grease from clothing, cleaning kid gloves, &c.
If pure it is in reality a most dangerous spirit, being very inflammable;
it is also extremely volatile, so much so that, if an uncorked bottle be
left in a warm room where there is a fire or other light near, its vapour
will probably ignite. Should the vapour become mixed with air before
ignition, it becomes a most dangerous explosive, and it will thus be seen
how necessary it is to handle the article in household use in a most
cautious manner. Being highly volatile, a considerable degree of cold is
experienced if a drop be placed on the hand and allowed to evaporate.
Benzene, which is only a compound of carbon and hydrogen, was first
discovered by Faraday in 1825; it is now obtained in large quantities
from coal-tar, not so much for use as benzene; is for its conversion, in
the first place, by the action of nitric acid, into _nitro-benzole,_ a
liquid having an odour like the oil of bitter almonds, and which is much
used by perfumers under the name of _essence de mirbane_; and, in the
second place, for the production from this nitro-benzole of the far-famed
_aniline_. After the distillation of benzene from the crude coal-naphtha
is completed, the chief impurities in the residue are charred and
deposited by the action of strong sulphuric acid. By further distillation
a lighter oil is given off, often known as _artificial turpentine oil_,
which is used as a solvent for varnishes and lackers. This is very
familiar to the costermonger fraternity as the oil which is burned in the
flaring lamps which illuminate the New Cut or the Elephant and Castle on
Saturday and other market nights.
By distillation of the _heavy oils_, carbolic acid and commercial
_anthracene_ are produced, and by a treatment of the residue, a white and
crystalline substance known as _naphthalin_ (C_{10}H_{8}) is finally
obtained.
Thus, by the continued operation of the chemical process known as
fractional distillation of the immediate products of coal-tar, these
various series of useful oils are prepared.
The treatment is much the same which has resulted in the production of
paraffin oil, to which we have previously referred, and an account of the
production of coal-oils would be very far from satisfactory, which made
no mention of the production of similar commodities by the direct
distillation of shale. Oil-shales, or bituminous shales, exist in all
parts of the world, and may be regarded as mineral matter largely
impregnated by the products of decaying vegetation. They therefore
greatly resemble some coals, and really only differ therefrom in degree,
in the quantity of vegetable matter which they contain. Into the subject
of the various native petroleums which have been found--for these
rock-oils are better known as petroleums--in South America, in Burmah
(Rangoon Oil), at Baku, and the shores of the Caspian, or in the United
States of America, we need not enter, except to note that in all
probability the action of heat on underground bituminous strata of
enormous extent has been the cause of their production, just as on a
smaller scale the action of artificial heat has forced the reluctant
shale to give up its own burden of mineral oil. However, previous to
1847, although native mineral oil had been for some years a recognised
article of commerce, the causes which gave rise to the oil-wells, and the
source, probably a deep-seated one, of the supply of oil, does not appear
to have been well known, or at least was not enquired after. But in that
year Mr Young, a chemist at Manchester, discovered that by distilling
some petroleum, which he obtained from a spring at Riddings in
Derbyshire, he was able to procure a light oil, which he used for burning
in lamps, whilst the heavier product which he also obtained proved a most
useful lubricant for machinery. This naturally distilled oil was soon
found to be similar to that oil which was noticed dripping from the roof
of a coal-mine. Judging that the coal, being under the influence of heat,
was the cause of the production of the oil, Mr Young tested this
conclusion by distilling the coal itself. Success attended his endeavour
thus to procure the oil, and indelibly Young stamped his name upon the
roll of famous men, whose industrial inventions have done so much towards
the accomplishment of the marvellous progress of the present century.
From the distillation he obtained the well-known Young's Paraffin Oil,
and the astonishing developments of the process which have taken place
since he obtained his patent in 1850, for the manufacture of oils and
solid paraffin, must have been a source of great satisfaction to him
before his death, which occurred in 1883.
Cannel coal, Boghead or Bathgate coal, and bituminous shales of various
qualities, have all been requisitioned for the production of oils, and
from these various sources the crude naphthas, which bear a variety of
names according to some peculiarity in their origin, or place of
occurrence, are obtained. Boghead coal, also known as "Torebanehill
mineral," gives Boghead naphtha, while the crude naphtha obtained from
shales is often quoted as shale-oil. In chemical composition these
naphthas are closely related to one another, and by fractional
distillation of them similar series of products are obtained as those we
have already seen as obtained from the crude coal-naphtha of coal-tar.
In the direct distillation of cannel-coal for the production of paraffin,
it is necessary that the perpendicular tubes or retorts into which the
coal is placed be heated only to a certain temperature, which is
considerably lower than that applied when the object is the production of
coal-gas. By this means nearly all the volatile matters pass over in the
form of condensible vapours, and the crude oils are at once formed, from
whence are obtained at different temperatures various volatile ethers,
benzene, and artificial turpentine oil or petroleum spirit. After these,
the well-known safety-burning paraffin oil follows, but it is essential
that the previous three volatile products be completely cleared first,
since, mixed with air, they form highly dangerous explosives. To the fact
that the operation is carried on in the manufactories with great care and
accuracy can only be attributed the comparative rareness of explosions of
the oil used in households.
After paraffin, the heavy lubricating oils are next given off, still
increasing the temperature, and, the residue being in turn subjected to a
very low temperature, the white solid substance known as paraffin, so
much used for making candles, is the result. By a different treatment of
the same residue is produced that wonderful salve for tender skins, cuts,
and burns, known popularly as _vaseline_. Probably no such
widely-advertised remedial substance has so deserved its success as this
universally-used waste product of petroleum.
We have noticed the fact that in order to procure safety-burning oils, it
is absolutely necessary that the more volatile portions be completely
distilled over first. By Act of Parliament a test is applied to all oils
which are intended for purposes of illumination, and the test used
consists of what is known as the flashing-point. Many of the more
volatile ethers, which are highly inflammable, are given off even at
ordinary temperatures, and the application of a light to the oil will
cause the volatile portion to "flash," as it is called. A safety-burning
oil, according to the Act, must not flash under 100° Fahrenheit open
test, and all those portions which flash at a less temperature must be
volatilised off before the residue can be deemed a safe oil. It seems
probable that the flashing-point will sooner or later be raised.
One instance may be cited to show how necessary it is that the native
mineral oils which have been discovered should have this effectual test
applied to them.
When the oil-wells were first discovered in America, the oil was obtained
simply by a process of boring, and the fountain of oil which was bored
into at times was so prolific, that it rushed out with a force which
carried all obstacles before it, and defied all control. In one instance
a column of oil shot into the air to a height of forty feet, and defied
all attempts to keep it under. In order to prevent further accident, all
lights in the immediate neighbourhood were extinguished, the nearest
remaining being at a distance of four hundred feet. But in this crude
naphtha there was, as usual, a quantity of volatile spirit which was
being given off even at the temperature of the surrounding atmosphere.
This soon became ignited, and with an explosion the column of oil was
suddenly converted into a roaring column of fire. The owner of the
property was thrown a distance of twenty feet by the explosion, and soon
afterwards died from the burns which he had received from it. Such an
accident could not now, however, happen. The tapping, stopping, and
regulating of gushing wells can now be more effectually dealt with, and
in the process of refining; the most inflammable portions are separated,
with a result that, as no oil is used in the country which flashes under
100° F. open test, and as our normal temperature is considerably less
than this, there is little to be feared in the way of explosion if the
Act be complied with.
When the results of Mr Young's labours became publicly known, a number of
companies were started with the object of working on the lines laid down
in his patent, and these not only in Great Britain but also in the United
States, whither quantities of cannel coal were shipped from England and
other parts to feed the retorts. In 1860, according to the statistics
furnished, some seventy factories were established in the United States
alone with the object of extracting oil from coal and other mineral
sources, such as bituminous shale, etc. When Young's patent finally
expired, a still greater impetus was given to its production, and the
manufacture would probably have continued to develop were it not that
attention had, two years previously, been forcibly turned to those
discoveries of great stores of natural oil in existence beneath a
comparatively thin crust of earth, and which, when bored into, spouted
out to tremendous heights.
The discovery of these oil-fountains checked for a time the development
of the industry, but with the great production there has apparently been
a greatly increased demand for it, and the British industry once again
appears to thrive, until even bituminous shales have been brought under
requisition for their contribution to the national wealth.
Were it not for the nuisance and difficulty experienced in the proper
cleaning and trimming of lamps, there seems no other reason why mineral
oil should not in turn have superseded the use of gas, even as gas had,
years before, superseded the expensive animal and vegetable oils which
had formerly been in use.
Although this great development in the use of mineral oils has taken
place only within the last thirty years, it must not be thought that
their use is altogether of modern invention. That they were not
altogether unknown in the fifth century before Christ is a matter of
certainty, and at the time when the Persian Empire was at the zenith of
its glory, the fires in the temples of the fire-worshippers were
undoubtedly kept fed by the natural petroleum which the districts around
afforded. It is thought by some that the legend which speaks of the fire
which came down from heaven, and which lit the altars of the
Zoroastrians, may have had its origin in the discovery of a hitherto
unknown petroleum spring. More recently, the remarks of Marco Polo in his
account of his travels in A.D. 1260 and following years, are particularly
interesting as showing that, even then, the use of mineral oil for
various purposes was not altogether unknown. He says that on the north of
Armenia the Greater is "Zorzania, in the confines of which a fountain is
found, from which a liquor like oil flows, and though unprofitable for
the seasoning of meat, yet is very fit for the supplying of lamps, and to
anoint other things; and this natural oil flows constantly, and that in
plenty enough to lade camels."
From this we can infer that the nature of the oil was entirely unknown,
for it was a "liquor like oil," and was also, strange to say,
"unprofitable for the seasoning of meat"! In another place in Armenia,
Marco Polo states that there was a fountain "whence rises oil in such
abundance that a hundred ships might be at once loaded with it. It is not
good for eating, but very fit for fuel, for anointing the camels in
maladies of the skin, and for other purposes; for which reason people
come from a great distance for it, and nothing else is burned in all this
country."
The remedial effects of the oil, when used as an ointment, were thus
early recognised, and the far-famed vaseline of the present day may be
regarded as the lineal descendent, so to speak, of the crude medicinal
agent to which Marco Polo refers.
The term asphalt has been applied to so many and various mixtures, that
one scarcely associates it with natural mineral pitch which is found in
some parts of the world. From time immemorial this compact, bituminous,
resinous mineral has been discovered in masses on the shores of the Dead
Sea, which has in consequence received the well-known title of Lake
Asphaltites. Like the naphthas and petroleums which have been noticed,
this has had its origin in the decomposition of vegetable matter, and
appears to be thrown up in a liquid form by the volcanic energies which,
are still believed to be active in the centre of the lake, and which may
be existent beneath a stratum, or bed, of oil-producing bitumen.
In connection with the formation of this substance, the remarks of Sir
Charles Lyell, the great geologist, may well be quoted, as showing the
transformation of vegetable matter into petroleum, and afterwards into
solid-looking asphalt. At Trinidad is a lake of bitumen which is a mile
and a half in circumference. "The Orinoco has for ages been rolling down
great quantities of woody and vegetable bodies into the surrounding sea,
where, by the influence of currents and eddies, they may be arrested, and
accumulated in particular places. The frequent occurrence of earthquakes
and other indications of volcanic action in those parts, lend countenance
to the opinion that these vegetable substances may have undergone, by the
agency of subterranean fire, those transformations or chemical changes
which produce petroleum; and this may, by the same causes, be forced up
to the surface, where, by exposure to the air, it becomes inspissated,
and forms those different varieties of earth-pitch or asphaltum so
abundant in the island."
It is interesting to note also that it was obtained, at an ancient
period, from the oil-fountains of Is, and that it was put to considerable
use in the embalming of the bodies of the Egyptians. It appears, too, to
have been employed in the construction of the walls of Babylon, and thus
from very early times these wonderful products and results of decayed
vegetation have been brought into use for the service of man.
Aniline has been previously referred (p. 135) to as having been prepared
from nitro-benzole, or _essence de mirbane_, and its preparation, by
treating this substance with iron-filings and acetic acid, was one of the
early triumphs of the chemists who undertook the search after the unknown
contained in gas-tar. It had previously been obtained from oils distilled
from bones. The importance of the substance lies in the fact that, by the
action of various chemical reagents, a series of colouring matters of
very great richness are formed, and these are the well-known _aniline
dyes_.
As early as 1836, it was discovered that aniline, when heated with
chloride of lime, acquired a beautiful blue tint. This discovery led to
no immediate practical result, and it was not until twenty-one years
after that a further discovery was made, which may indeed be said to have
achieved a world-wide reputation. It was found that, by adding bichromate
of potash to a solution of aniline and sulphuric acid, a powder was
obtained from which the dye was afterwards extracted, which is known as
_mauve_. Since that time dyes in all shades and colours have been
obtained from the same source. _Magenta_ was the next dye to make its
appearance, and in the fickle history of fashion, probably no colours
have had such extraordinary runs of popularity as those of mauve and
magenta. Every conceivable colour was obtained in due course from the
same source, and chemists began to suspect that, in the course of time,
the colouring matter of dyer's madder, which was known as _alizarin_,
would also be obtained therefrom. Hitherto this had been obtained from
the root of the madder-plant, but by dint of careful and well-reasoned
research, it was obtained by Dr Groebe, from a solid crystalline coal-tar
product, known as _anthracene_, (C_{12}H_{14}). This artificial alizarin
yields colours which are purer than those of natural madder, and being
derived from what was originally regarded as a waste product, its cost of
production is considerably cheaper.
We have endeavoured thus far to deal with (1) gas, and (2) tar, the two
principal products in the distillation of coal. We have yet to say a few
words concerning the useful ammoniacal liquor, and the final residue in
the retorts, _i.e._, coke.
The ammoniacal liquor which has been passing over during distillation of
the coal, and which has been collecting in the hydraulic main and in
other parts of the gas-making apparatus, is set aside to be treated to a
variety of chemical reactions, in order to wrench from it its useful
constituents. Amongst these, of course, _ammonia_ stands in the first
rank, the others being comparatively unimportant. In order to obtain
this, the liquor is first of all neutralised by being treated with a
quantity of acid, which converts the principal constituent of the liquor,
viz., carbonate of ammonia (smelling salts), into either sulphate of
ammonia, or chloride of ammonia, familiarly known as sal-ammoniac,
according as sulphuric acid or hydrochloric acid is the acid used. Thus
carbonate of ammonia with sulphuric acid will give sulphate of ammonia,
but carbonate of ammonia with hydrochloric acid will give sal-ammoniac
(chloride of ammonia). By a further treatment of these with lime, or, as
it is chemically known, oxide of calcium, ammonia is set free, whilst
chloride of lime (the well-known disinfectant), or sulphate of lime
(gypsum, or "plaster of Paris" ), is the result.
Thus:
Sulphate of ammonia + lime = plaster of Paris + ammonia.
or,
Sal-ammoniac + lime = chloride of lime + ammonia.
Ammonia itself is a most powerful gas, and acts rapidly upon the eyes. It
has a stimulating effect upon the nerves. It is not a chemical element,
being composed of three parts of hydrogen by weight to one of nitrogen,
both of which elements alone are very harmless, and, the latter indeed,
very necessary to human life. Ammonia is fatal to life, producing great
irritation of the lungs.
It has also been called "hartshorn," being obtained by destructive
distillation of horn and bone. The name "ammonia" is said to have been
derived from the fact that it was first obtained by the Arabs near the
temple of Jupiter Ammon, in Lybia, North Africa, from the excrement of
camels, in the form of sal-ammoniac. There are always traces of it in the
atmosphere, especially in the vicinity of large towns and manufactories
where large quantities of coal are burned.
Coke, if properly prepared, should consist of pure carbon. Good coal
should yield as much as 80 per cent. of coke, but owing to the
unsatisfactory manner of its production, this proportion is seldom
yielded, whilst the coke which is familiar to householders, being the
residue left in the retorts after gas-making, usually contains so large a
proportion of sulphur as to make its combustion almost offensive. No
doubt the result of its unsatisfactory preparation has been that it has
failed to make its way into households as it should have done, but there
is also another objection to its use, namely, the fact that, owing to the
quantity of oxygen required in its combustion, it gives rise to feelings
of suffocation where insufficient ventilation of the room is provided.
Large quantities of coke are, however, consumed in the feeding of furnace
fires, and in the heating of boilers of locomotives, as well as in
metallurgical operations; and in order to supply the demand, large
quantities of coal are "coked," a process by which the volatile products
are completely combusted, pure coke remaining behind. This process is
therefore the direct opposite to that of "distillation," by which the
volatile products are carefully collected and re-distilled.
The sulphurous impurities which are always present in the coal, and which
are, to a certain extent, retained in coke made at the gas-works,
themselves have a value, which in these utilitarian days is not long
likely to escape the attention of capitalists. In coal, bands of bright
shining iron pyrites are constantly seen, even in the homely scuttle, and
when coal is washed, as it is in some places, the removal of the pyrites
increases the value of the coal, whilst it has a value of its own.
The conversion of the sulphur which escapes from our chimneys into
sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol,
has already been referred to, and we can only hope that in these days
when every available source of wealth is being looked up, and when there
threatens to remain nothing which shall in the future be known as
"waste," that the atmosphere will be spared being longer the receptacle
for the unowned and execrated brimstone of millions of fires and
furnaces.