GAS LIGHTING.
The invention of Gas Lighting had its origin in the earliest times of history; not, indeed, as we now see it, burning at the end of a pipe supplied with gas made artificially, and stored in gas-holders, but blazing from fissures in the ground, supplied from natural sources in the bowels of the earth. The Greek fire-altars are supposed to have been supplied with gas, either issuing from bituminous beds, or made artificially by the priests, by pouring oil on heated stones placed in cavities beneath. Fountains of naphtha, and fires issuing from the earth at Ecbatana, in Media, are mentioned by Plutarch in his life of Alexander, and many other ancient historians record the knowledge of similar instances of natural gas lighting.
In later times, the inflammable gas issuing into the galleries of coal mines, and either exploding when mixed with atmospheric air, or blazing as it issued from fissures in the coal, afforded instances of the natural production of gas, the ignition of which too frequently proved fatal to those in the mines.
A remarkable instance of the issue of inflammable gas into the shaft of a coal mine at Whitehaven, which produced a blaze about 3 feet diameter and 6 feet long, is noticed in the "Philosophical Transactions" of 1733. The part whence the gas issued was vaulted off, and a tube was inserted into the cavity and carried to the top of the pit, where it escaped in undiminished quantity for years, and lighted the country for a distance of several miles. Many experiments were made with this large issue of gas, and it was proposed to conduct it in pipes to Whitehaven, to light the streets of that town, but the proposition was rejected by the local authorities.
In China, naturally produced gas is used on a large scale, and was so long before the knowledge of its application was acquired by Europeans. Beds of coal, lying at a great depth, are frequently pierced by the borers for salt water, and from these wells the inflammable gas springs up. It sometimes appears as a jet of fire from 20 to 30 feet high; and, in the neighbourhood of Thsee-Lieon-Teing, the salt works were formerly heated and lighted by means of these fountains of fire. Bamboo pipes carry the gas from the spring to the places where it is intended to be consumed. These canes are terminated by tubes of pipe-clay, to prevent their being burnt, and other bamboo canes conduct the gas intended for lighting the streets, and into large apartments and kitchens. Thus Nature presents in these positions a complete establishment of gas-light works.9
Though the production of illuminating gas from natural sources had been thus long known, the idea of distilling it artificially from coal, for the purpose of illumination, did not occur until the end of the last century. Dr. Clayton, indeed, nearly arrived at the practical application of carburretted hydrogen, in 1737, for he instituted experiments to prove that coal contains gas, nearly similar to that of the "fire damp" in coal mines, and that it burns with a bright flame. At that time, however, the nature of gases was so imperfectly known, that he was unable to do more than discover that coal possesses the property of giving out, when heated, gas that will burn with a bright light.
In the "Philosophical Transactions" of 1739, Dr. Clayton thus describes the effect of the "spirit of coal," obtained by destructive distillation in an iron retort. "I kept this spirit," he says, "in bladders for a considerable time, and endeavoured several ways to condense it, but in vain; and when I had a mind to divert strangers or friends, I have frequently taken one of these bladders, and pierced a hole in it with a pin, and, compressing gently the bladder near the flame of a candle till it once took fire, it would then continue flaming till all the spirit was compressed out of the bladder; which was the more surprising, because no one could discern any difference in the appearance between these bladders and those which were filled with common air."
The first known application of coal gas to illumination was made, in 1792, by Mr. William Murdoch, engineer at the Soho manufactory, to whose great ingenuity the world is also indebted for the invention of the first plan of a steam locomotive engine.10 He was at that time occupied in superintending the fitting up of steam engines for the Cornish mines, and his attention having been directed to the properties of gas issuing from coal, he instituted a series of experiments on carburretted hydrogen, the practical result of which was the lighting of his house and offices, at Redruth, with coal gas. The mines at which Mr. Murdoch worked being some miles distant from his house, he was in the constant practice of filling a bladder with coal gas, in the neck of which he fixed a metallic tube with a small orifice, through which the gas issued. The lighted gas issuing through the tube served as a lantern to light his way; and as he thus proceeded along the road with the light issuing from the bladder, the country people looked upon him as a wizard.
The gas was generated by Mr. Murdoch in an iron retort, and collected in a common gasometer, from which it was conducted in pipes to the rooms to be lighted. He also, in an early stage of the invention, contrived a means for making the gas portable, by compressing it into strong vessels; a plan which, a few years since, was adopted by the Portable Gas Company in London.
Mr. Murdoch having proved the practicability of illumination by gas generated from coal, he continued his experiments to facilitate the manufacture of the gas on a large scale, and for its more perfect purification.
The first public display of its illuminating power was made at the rejoicings for the peace of Amiens, in 1802, on which occasion part of the work-shops of Messrs. Boulton and Watt, at Soho, was brilliantly illuminated with coal gas by Mr. Murdoch. In 1805, Messrs. Phillips and Lee, of Manchester, had their extensive cotton mill fitted up with gas apparatus, under the superintendence of Mr. Murdoch, and the quantity of light given out by the burners in all parts of the cotton mill was equal to that of 3,000 candles.11
Notwithstanding these eminently successful trials of gas lighting, the prejudice against innovation prevented, for several years, the extensive adoption of the plan. As every establishment using gas had to make it, and as the apparatus was costly and imperfectly managed, the expense in the first instance, the trouble, and the noxious smell, presented great obstacles to the introduction of that mode of illumination. The popular notion, also, that streams of flame were rushing along the pipes produced an impression that gas lighting must be very dangerous, which it required time to disprove. It was not, therefore, till several years after the advantages and economy of gas had been practically established, that a public company was formed for laying down pipes to light the streets, and to convey the gas into houses for lighting shops.
The person to whom the world is chiefly indebted for the practical application of gas lighting is Mr. Winsor, who had been a merchant in London. Being very sanguine as to the advantages to be derived from gas lighting, and possessing an ardent temperament which no opposition could quench, he undertook to introduce it to public notice, and to form a company for lighting the whole of England with gas. He hired the old Lyceum Theatre, which he lighted with coal gas, and he there delivered lectures and exhibited experiments to show the benefits that would arise from the universal use of gas light, and coke fuel. He published an extravagant prospectus of a company to be formed, with the following title:—"A National Light and Heat Company, for providing our streets and houses with light and heat, on similar principles as they are now (1816) supplied with water. Demonstrated by the patentee at No. 97, Pall Mall, where it is proved, by positive experiments and decisive calculation, that the destruction of smoke would open unto the empire of Great Britain new and unparalleled sources of inexhaustible wealth at this most portentous crisis of Europe. The serious perusal of this publication, and an attentive observation of the decisive experiments, will carry conviction to every mind."
In this prospectus Mr. Winsor attempted to make it appear that by adopting his plan there would be "a grand balance of profit for the whole realm of £115,000,000," and each shareholder of the company was promised, "at the lowest calculation, £570 for every £5 deposit." He entertained the notion of making the use of gas and coke compulsory, by levying a tax on all who obstinately refused to adopt what would be so much to their own advantage. This tax, he said, "cannot be oppressive in the least, because it falls on the obstinate only, who shall resist the use of a far superior, cheaper, and safer fuel." Not content with the language of prose, Mr. Winsor vented his thoughts and feelings in numerous poetical effusions. The flights of his Muse, however, were not into the regions of sublimity, as may be perceived by the following specimen:—
"Must Britons be condemned for ever to wallow
In filthy soot, noxious smoke, train oil, and tallow,
And their poisonous fumes for ever to swallow?
For with sparky soot, snuffs and vapours, men have constant strife,—
Those who are not burned to death are smothered during life."
Mr. Winsor's absurd statements—in the truth of which he potently believed—and the wild, random manner of making them known, excited much ridicule and opposition. Among his opponents was Mr. Nicholson, the editor of the Chemical Review, who not only challenged Mr. Winsor's estimates, but the validity of his patent, on the ground that Mr. Murdoch was the original inventor. Mr. Winsor's plans and calculations were burlesqued in a cleverly written "Heroic Poem," published in a quarto volume, which, whilst professing to extol the virtues of gas and coke, quizzed its hero most unmercifully. The poem concluded with this address:—
"And when, ah, Winsor!—distant be the day!—
Life's flame no longer shall ignite thy clay,
Thy phosphur nature, active still, and bright,
Above us shall diffuse post obit light.
Perhaps, translated to another sphere,
Thy spirit—like thy light, refined and clear—
Ballooned with purest hydrogen, shall rise,
And add a PATENT PLANET to the skies.
Then some sage Sidrophel, with Herschel eye,
The bright Winsorium Sidus shall descry;
The Vox Stellarum shall record thy name,
And thine outlive another Winsor's fame."
"Though we may smile at Mr. Winsor's extravagant plans and calculations," observes the Journal of Gas Lighting, "we cannot but admire the enthusiasm with which he pursued his object, and ultimately succeeded in establishing the first gas company. The lighting of Pall Mall with gas, in the spring of 1807, gave increased stimulus to the project, and application was made to Parliament to carry it into effect. The bill was opposed by Mr. Murdoch and thrown out; but in the following year (1810) the application was successfully renewed. The scheme, however, as sanctioned by Parliament, was sadly shorn of its magnificent proportions; and, instead of a 'Grand National Light and Heat Company, for Lighting and Heating the Whole Kingdom,' its operations were limited to London, Westminster, and Southwark; nor were any special taxes imposed on those who should obstinately refuse to use the light and burn the coke. The Chartered Gas Company, established by Mr. Winsor's persevering efforts, has served as the guiding star to all other gas companies in the world."
The illuminating property of coal gas depends on the quantity of carbon it contains. Pure hydrogen gas burns with a pale blue flame that gives scarcely any light, though it possesses intense heating power. If, however, minute particles of a solid body—powdered charcoal, for instance—be thrown into the flame, they become white-hot, and the incandescence of those solid particles produces a brilliant light. The same effect is caused by the combustion of the carburretted hydrogen gas, and in a more perfect manner. That gas contains a large portion of carbon in a state of vapour, and when a light is applied to a jet of the gas the hydrogen immediately inflames, the carbon is deposited in the flame, and the minute particles into which it is disseminated become highly heated and ignite.
There are two distinct states of carbonization in illuminating gas. The commoner kind—the ordinary coal gas—consists of two measures of hydrogen mixed with one measure of carbon vapour. The specific gravity of such gas is about one-half that of atmospheric air, and it is eight times heavier than pure hydrogen.12 The best kind of gas for illumination is obtained from the distillation of oil. It is called olefiant gas, and contains equal measures of hydrogen gas and carbon vapour; its specific gravity is 0.985, being about fifteen times heavier than pure hydrogen.
The rationale of the process of making coal gas consists in expelling the volatile matters from the coal by heat, in closed vessels or retorts, and then separating the gas and purifying it on its passage from the retort to the gas-holder, where it is stored for use.
The retorts are usually made of cast iron, and are about 7 feet long, 14 inches in depth, and the same in width; the shape being that of an arch. The retorts will hold two hundredweight of coal each, but they are never filled, because during the process of distillation the carbonaceous part of the coal expands, and occupies more space than the original quantity, the proportion of expansion being as one and a quarter to one. There is a large aperture for the admission of coal and the extraction of coke, which aperture is covered with a lid, and screwed to make it air-tight. A tube is inserted into the mouth of the retort, to carry off the products of the distillation. That tube rises about twelve feet, and then dips into a large horizontal pipe, one foot in diameter, called the hydraulic main, in which are collected the tar and ammoniacal liquor that distil from the coal. Ten or fourteen retorts are usually set back to back in brickwork, to be heated by one fire; but the plan has been recently introduced of employing long clay retorts, which are charged at both ends. These are found to possess considerable advantage over iron, not only from their lower price, but from the facility with which the carbonaceous deposit is removed, and the full charges worked off. Coke is generally burned in the furnaces, and the heat is continually maintained so as to keep the retorts red-hot.
As atmospheric air cannot gain access to the coal in the retorts, the gases expelled do not inflame, nor can the parts that are not volatile be consumed without a supply of air. It is entirely a process of distillation, in which all the products can be collected. The volatile parts are carried off by the pipe, and the solid carbonaceous matter, or coke, is left in the retort.
The first effect of heat on coal, after it is put into the retort, is to expel the moisture, which, in combination with the air, issues in the form of steam. Tar then distils, with some portions of gas, consisting of hydrogen and ammonia. When the retort has attained a bright cherry-red heat, the disengagement of the carburretted hydrogen is most active; and it is found that the more quickly the coal is heated, the greater is the quantity of illuminating gas generated.
The production of coal gas, and the development of its properties at different stages of distillation, may be readily shown by means of a common tobacco pipe. Fill the bowl of the pipe with small pieces of coal, cover it over with a lump of clay, and then put it into a hot fire, with the stalk of the pipe projecting through the bars. Presently steam will be seen to issue from the pipe, and afterwards smoke, and, if a light be applied, a jet of flame will issue forth, the brilliancy of which will increase as the bowl of the pipe becomes more heated, until the best part of the gas has been distilled from the coal.
The gas is mingled with various volatile products as it issues from the retort, and requires to be purified before it is fitted for illumination. The most abundant matter that passes over with it is tar. The vapour of that substance, however, condenses when cooled, and it may thus be separated from the gas very effectually. For that purpose the gas, after having deposited a large portion of the tar in the hydraulic main, is made to traverse through a number of vertical pipes, and in passing through them a further quantity of tar, accompanied by ammoniacal liquor, is deposited, and collected in a reservoir at the bottom. The next process is the purification of the gas from carbonic acid and sulphuretted hydrogen. This is commonly done by passing it through water and lime; the combination of the carbonic acid with the lime being facilitated by agitation. The method of purifying by lime was introduced by Mr. Clegg; and by a later process, oxide of iron is used to absorb the sulphuretted hydrogen. The gas, when purified, is conveyed to the gas-holder, whence it is forced by pressure into the mains and pipes.
An apparatus for generating coal gas on a small scale for private establishments, remote from sources of ordinary supply, is represented in the accompanying woodcut. The retort, A, is fitted in a small furnace. The coal is put in at F, and the products of distillation pass through the bent pipe, E. The more liquid portions of the tar pass at once through the tube, B, into the receiver, G; and as the gas passes along the bent tube, C, it becomes cooled, and a further deposit of tar and ammoniacal liquor is made. The gas is then conveyed along another tube into the purifier, H, filled with lime and water, and it thence passes into the gas-holder. Tubes are inserted into the latter for conveying the gas to the burners.
The quantity and the quality of the gas yielded by coal differ materially according to the kind employed. One ton of good Newcastle coal will yield 9,500 cubic feet of gas, which, when burnt in the best manner, gives a light equal to that of 422 lbs. of spermaceti candles. One ton of Wigan cannel coal yields 10,000 cubic feet, and gives a light equal to 747 lbs. of spermaceti candles.13 The price, in London, of good gas from Newcastle coal, is 4s. 6d. per thousand cubic feet, which gives a light equal to 74½ lbs. of spermaceti, and equal to 89 lbs. of mould candles; therefore, when the latter are 8d. a pound, the burning of gas is twelve times more economical than the burning of candles. In Liverpool, gas from cannel coal is supplied at the low price of 3s. 9d. per thousand feet; and that gas gives at least one-third more light than the ordinary London gas.
The cleanliness of gas, as compared with candles or oil, is a further recommendation; and for the purpose of lighting streets, shops, factories, public buildings, and halls, it presents important advantages; but it is not well adapted for small sitting rooms, because the heat of the flame makes it unpleasant and injurious to the eyes when near, and, unless very pure, it deteriorates the air of closed apartments. In many parts of the country, however, where coals are cheap, and the price of gas is consequently less than in London, it is introduced into every room of nearly all private houses.
The best kind of gas made from mineral substances is produced by the distillation of a bituminous shale, called Boghead coal, which was discovered a few years since in Scotland. One ton of this material yields 15,000 cubic feet of gas, which is equal in illuminating power to 1,930 lbs. of sperm candles. Boghead coal is now commonly used for mixing its gas with that of inferior quality, to bring up the illuminating power to the required standard.
Olefiant gas, made from oil, burns with a brighter and purer light than common coal gas, but it is more costly. It is made nearly in the same manner, by distillation in retorts; the principal difference consisting in the degree and regulation of the temperature. A dull red heat is the best, and in order to keep the oil exposed to the action of an invariable heat, it is admitted gradually into the retorts, into which pieces of brick or coke are inserted to increase the heating surface. One pound of common oil yields about 15 feet of olefiant gas. The same kind of gas may also be obtained in smaller quantities by the distillation of tar, rosin, or pitch. Twelve cubic feet of gas may be obtained from one pound of tar, and ten from the same weight of rosin.
The brilliancy of gas-light depends, in some measure, on the kind of burner employed. To obtain a steady light, an argand burner is usually adopted; the gas being allowed to escape through a number of minute holes pierced in a hollow ring of metal, which admits a current of air through the middle. To increase the supply of air, the burner is covered with a glass chimney, which, if not too long, adds to the brilliancy of the flame; but a very long chimney produces so strong a current of air, as to cool the flame, and diminish the light. A plan is sometimes adopted of placing a small metal disc a short distance above the jets, so as to spread the flame. By this means the brightness is increased, by exposing the flame more directly to the current of air; and the metal disc, by becoming heated, also tends to aid the combustion of the carbon.
One of the problems to be solved on the original formation of gas works was the size of pipes, and the amount of pressure required to force the gas to the various burners. It was at first supposed that the friction against the pipes would oppose so much resistance to the passage of the gas, that it could not be transmitted to great distances. It was found, however, that the perpendicular pressure of a few inches of water was quite sufficient to force the gas through the mains and small pipes of an extensive range of streets. A bold attempt was made at Birmingham, in 1826, to bring gas from the collieries, at a distance of ten miles from the town. The plan was laughed at by many as impracticable, but it was attended with complete success. The gas being made near the mouth of the coal-pit, the cost of conveyance was saved by the additional outlay in the first instance. It must be observed, however, that it is extremely difficult in practice to avoid the escape of gas at the junctions of the pipes; and by increasing the length of the gas mains, the greater will be the leakage. The loss from this cause, in some gas works, exceeds 20 per cent. of the gas manufactured.
The volume of gas discharged from a pipe is directly proportional to the square of its diameter, and inversely as the square of its length. Thus, if a pipe required to discharge 250 cubic feet of gas in an hour, at a distance of 200 feet, must have an internal diameter of 1 inch; to discharge 2,000 feet in an hour, at a distance of 1,000 feet, would require a diameter of 4·47 inches. The same quantity discharged at double the distance would require a pipe 5·32 inches in diameter; at a distance of 4,000 feet the diameter must be increased to 6·13 inches; and at a distance of 6,000 feet the diameter should be 7 inches.
On the first introduction of gas-light, the companies who supplied it charged a fixed sum for each burner of a given size. This mode of charging was, however, very unsatisfactory, for the size of the burner is a very uncertain indication of the quantity of gas consumed. Persons using gas desired to pay for the quantity they actually burned; and to enable them to do this, a special contrivance was invented by Mr. Clegg, the engineer of the Chartered Gas Company, called a gas-meter. That instrument measures, with sufficient accuracy for practical purposes, the volume of gas that passes through it to the burners, and thus each consumer of gas now pays only for the number of cubic feet consumed.
The accompanying diagrams represent sections of a gas meter, as seen in front and edgewise. The outer case of the instrument, which is a flat cylinder made of sheet iron, is indicated by the letters c, c. Inside it there revolves another cylinder, made also of thin sheet iron, and divided into four compartments, marked d, d, d, d. This interior cylinder readily revolves on an axis, g, g, shown in the section of the instrument as seen edgewise. The gas enters from the street pipe through the opening, a, and it is forced out to the burners through the pipe, b, the latter being seen in the narrow section only. In that diagram, also, there is shown a cog-wheel, h, fixed on to the axis, and a small outer case, in which that wheel rotates. Water is poured into that external case until the gas-meter is rather more than half filled, the level of the water being shown at i.
The action of the instrument will be readily understood by examining the two sections. The gas, on entering the tube, a, presses against the upper surface of the compartment that happens to be then above it, and tends to turn the inner cylinder round. This pressure forces the gas through the opening, b, to the burner; and as the compartment then in communication with that opening is emptied of the gas it contains, in the direction of the arrow, it is gradually forced under the level of the water, and the other compartment, which has in the meantime been filling with gas, continues the supply. Thus, supposing each division of the inner revolving cylinder to hold 108 cubic inches, a complete revolution would indicate that the fourth part of a cubic foot had passed through the pipe, b, to the burners. Several cog-wheels, arranged like clock-work mechanism, are connected with the wheel, g, and by this means the number of cubic feet of gas consumed is indicated by hands fixed to the wheels, and pointing to the corresponding figures on a series of dials.
Some inconvenience and irregularity having been experienced in the use of the wet meter, the correctness of which, it is evident, may be affected by variations in the height of the water level, dry meters have been constructed for measuring gas, by causing it to pass through a small expanding chamber, similar in principle to a pair of bellows. The objection to these instruments is that the leather, or other flexible substance that forms the sides of the expanding chambers, becomes rigid by use, and the valves are liable to get out of order; but in the last improvement of the instrument, by Mr. Croll, these objections are stated to be effectually removed.
Numerous attempts have been made to produce illuminating gas from other substances than coal, but without advantage. The plan that promised the most success was the production of hydrogen gas by the decomposition of water, which was passed over heated coke in retorts, and by that means the oxygen of the water, combined with the incandescent coke and the hydrogen, was set free. The gas thus collected possessed little illuminating power, but it was afterwards mixed with the rich gas from cannel coal, and raised to the requisite illuminating standard. It was found, however, in practice, that the compound gas thus formed was more costly than ordinary coal gas, and the plan has been discontinued. Another method of giving illuminating power to water gas was to surround the flame with platinum gauze, which was rendered incandescent by the heat, and became highly luminous. But it required twice the quantity of gas burned in this manner to produce a light equal to that of carburretted hydrogen, and the combustion of so much hydrogen gas produced an amount of vapour and heat that were very unpleasant. That mode of gas illumination, called the "Gillard light," from the name of the inventor, was also found more costly than the ordinary mode of lighting with coal gas, which has now no rival to compete with it in economical illumination.
No Act of Parliament is now required, as originally proposed by Mr. Winsor, to enforce the burning of coal gas. Its advantages, in point of economy, cleanliness, and even of safety, are sufficiently understood to spread the use of coal gas to every part of the kingdom. In the metropolis alone there are twelve gas companies, who receive for the sale of gas an average of £100,000 per annum each, thus making the sum paid for gas lighting in London £1,200,000, and it has been estimated as high as £2,000,000. Taking the average price to be 4s. 6d. per thousand cubic feet, the quantity of gas consumed amounts to 5,300,000,000 cubic feet; and if we add to that quantity 20 per cent. for leakage through the mains and pipes, the quantity of gas manufactured in the metropolitian gas works is upwards of 6,000,000,000 cubic feet in a year. It may, perhaps, give a clearer notion of this immense quantity to say, that a gas-holder, capable of containing it, would require to be one mile in diameter, and the height of St. Paul's Cathedral. The light produced by burning such a volume of gas would be equal to that of 150,000 tons of mould candles, which would cost £13,000,000. The quantity of coals requisite for the production of the gas manufactured annually in London is upwards of 600,000 tons.