Suppose, for instance, that the pendulum is about to rise to the right towardss, at which time the voltaic circuit is completed. The coil is, therefore, magnetic, and is attracted by the permanent magnetinC. As the pendulum approaches the end of its swing, it pushes the movable bridge away from the gold studs on which it rests, and thus breaks connection with the voltaic battery, and the pendulum descends unrestrained by the attractive force of the magnets. As the pendulum descends towards its lowest point, it shifts the bridge on to the metal studs on the other side, which are so disposed as to send a current through the coil in a direction opposite to the former, so that the poles of the voltaic battery are reversed, and the attractive force is exerted in drawing the pendulum towards the left hand. In this manner the power imparted to the coil, as the pendulum vibrates to and fro, produces a continuous repetition of the attraction on each side alternately, and maintains a constant action.
The only wheels required in a clock of this kind are those which turn the hands; and the motion is communicated from the pendulum to the seconds wheel by means of a small attached lever, working on a ratchet wheel. The minute and the hour hands derive their movements from the seconds wheel in the usual manner.
The voltaic battery employed to work Mr. Bain's clocks consists of a pair of large copper and zinc plates buried in the moist earth, which excite a sufficient amount of electricity to maintain the motion of the pendulum. A battery of this kind will remain in action a long time, and will serve to keep a clock going for several months. It is, indeed, a near approach to the attainment of perpetual motion,since nothing but the wearing away of the materials, or the accumulation of dust on the connecting points, seems to prevent the realization of that mechanical chimera.
There is a disadvantage attending the arrangement of Mr. Bain's clocks, arising from the attachment of the pendulum to the wheels; and as the moving force is derived directly from voltaic electricity, any variation in the power of the battery causes variation in the lengths of the vibrations, and produces irregularity. For the purpose of remedying these defects, Mr. Shepherd, junior, has adopted an arrangement which detaches the pendulum from the clock movement, and makes its vibrations altogether independent of the varying force of voltaic batteries.
In Mr. Shepherd's arrangement, the impulse of the pendulum is given by successive blows from a spring, which is drawn back and then liberated at each vibration. The hands of the clock are also moved by electro-magnets, by which means the impelling forces and the resistances encountered by the pendulum are always constant. By making the pendulum thus independent of the works, and employing it merely to make and break contract at regular intervals, any number of clocks in the same establishment may be set in motion, and kept exactly together, by a single pendulum.
The large clock over the principal entrance to the Great Exhibition was on this construction. It would have been impossible, with any approach to regularity, to have moved hands of that size, exposed as theywere to the wind, unless the pendulum had been independent of such resistances.
Electro-Magnetic Clocks have not yet come into general use, partly owing to imperfections in the battery connections, which occasionally put a stop to their movements, but principally on account of the high prices charged by the patentees. As no trains of wheels are requisite in an Electro-Magnetic Clock, it might be manufactured very cheaply; and when the price is reduced to its proper standard, and the trifling practical defects are remedied, these clocks may possibly supersede others.
The electrotype, electro-gilding and plating, and the other applications of the deposition of metals from their solutions, by the agency of voltaic electricity, had their origin in the chance observation of peculiarities in frequently repeated experiments. In this, as in most other inventions, there are contending claimants for priority; but there is little merit due to any of the first discoverers of the process, who seem to have been guided altogether by accident. It seems strange, now, on observing the extensive use that is made of the deposition of metals, that it should have remained so long unapplied after the principle had been known.
The "revivification," as it was called, of metals from their solutions by voltaic electricity, was known at the beginning of the present century; for, in 1805, Brugnatelli, an Italian chemist, gilded a silver medal by connecting it with the negative pole of a voltaic battery, when immersed in a solution of ammoniuret of gold. It did not occur to him, however, that any use could be made of that mode of gilding, and the experiment had no result.
Nothing further was done, even experimentally, towards advancing the art of electrotyping, until Mr. Spencer, of Liverpool, when experimenting with a Daniell's battery, in 1837, accidentally coated a penny piece with copper; and when the thin sheet of metal was removed, he found on it an exact counterpart of the head and letters of the coin. Even this did not suggest any useful application; nor was it until, by a further accident, a drop of varnish fell on the copper of the negative pole, and showed that no deposition took place on the part so covered, that the idea occurred to him of turning the deposition of the copper to account. The method he adopted of doing so was to cover a copper plate with varnish or wax, and to etch a design through the covering. By then exposing the plate to the action of a solution of sulphate of copper, when in connection with the negative pole of a voltaic battery, the metal was deposited in the lines drawn through the varnish, and a design in relief was fixed to the copper. This slight advance in the art was not made known until it was announced, in 1839, that Professor Jacobi, of St. Petersburg, had made application of the same process. Mr. Spencer, indeed, was forestalled, even in this country, by Mr. Jordan, a printer, who published an account in theMechanics' Magazinefor May, 1839, of a method of making copper casts by the deposition of copper from its solution. In the autumn of the same year, however, Mr. Spencer exhibited to the British Association several more perfect specimens of electrotyping, that showed the process might be rendered valuable; and from thattime rapid progress was made in bringing it into practical operation in a variety of ways.
The deposition of copper from its solution, when under the action of voltaic electricity, is not produced by the decomposition of the sulphate of copper, as might be supposed, but by the decomposition of the water that acts as the solvent of the metallic salt. Thus, when two platinum wires from the poles of a voltaic battery are introduced into acidulated water, hydrogen gas is disengaged at the wire connected with the negative pole, and oxygen at the other; but when a solution of sulphate of copper is substituted for water, the hydrogen that is disengaged combines with the oxygen that held the copper in solution, and the metal is liberated. The copper thus liberated from its combination with the oxygen is deposited, in a pure metallic state, on the surface connected with the negative pole of the battery.
The simplest illustration of electro-metallic deposition is obtained by immersing a silver spoon and a strip of zinc into a solution of sulphate of copper. So long as the two metals are kept apart, no change takes place on the silver, but on bringing them into contact, voltaic action immediately commences, and a coating of copper is deposited upon the spoon, and adheres firmly to the metal. If the action be continued, and the supply of copper be maintained by the addition of fresh crystals of the sulphate, the coat of copper may be increased in thickness to almost any extent.
The first applications of the discovery were directedto the copying of medals and coins. An impression of the metal was obtained in fusible metal, which is an alloy composed of tin, lead, and bismuth, melted together in the proportions of two of the latter to one each of the former. This alloy expands on cooling, and thus affords a very sharp impression of the medals; and as it melts at a low temperature, it may be easily removed after the copper coating has been deposited upon it.
An electrotype mould, obtained directly from the medal, is, however, more sharp in its definition than an impression, and is therefore preferable, when circumstances admit of its being so taken. For that purpose, the surface whereon the deposition is to be made is smeared over with sweet oil, or with black lead. It is then carefully wiped with cotton wool, but a minute quantity of the oil will still remain, sufficient to prevent the metal from adhering.
A simple form of apparatus for the electrotype process is shown in the accompanying diagram.
An earthenware jar,a, serves to hold the solution of copper, which should be maintained in a saturated state by the addition of crystals of the salt. A porous tube,b, holds a rod of amalgamated zinc, to the top of which a binding-screw is soldered. The copper mould or medal,c, is suspended in the solution by a wire, which is held tight by the binding-screw,d. The porous jar is then filled to the same height as the copper solution in the jar with diluted sulphuric acid, in the proportions of one of acid to twenty of water.Voltaic action immediately commences, and the copper will continue to be deposited from the solution as long as the supply of fresh crystals of sulphate of copper is continued. In about twenty-four hours the coating of copper will be as thick as a thin card, and it may be then removed. When detached from the medal, it will be found to be an exact counterpart, in the minutest details, of the original; those parts of the medal which are in relief being, of course, the reverse in the mould.
The extreme minuteness and delicacy of the electrotype process is strikingly exemplified in its application to the transference of engraved copper-plates. A highly finished engraved copper-plate has a film of metal deposited over its whole surface, which, when detached, exhibits all the lines that are cut into the copper-plate in relief. That electrotype cast then serves as the mould for further depositions, in which every line in the original engraving is so perfectly developed, that it is impossible to detect a difference in the impressions taken from the two plates. By this means any number of casts may be made and worked from, whilst the original is preserved uninjured. The objection to this application is that the metal depositedis not so hard as the hammered plates, and will not, therefore, bear the wear and tear of copper-plate printing so well as the plates made by hand.
It was at one time supposed that the depositing of metal on surfaces, by voltaic action, might be applied to the manufacture of numerous kinds of copper articles without manual labour. For this purpose, casts were made of plaster of Paris, which were covered with black lead, to give them the property of conducting electricity, and the metal was then deposited upon them. But, independently of the practical difficulties attending the operation, it was found that the metal was not sufficiently hard, and the cost of the requisite voltaic batteries rendered the economy of the process questionable.
One of the successful applications of Electro-Metallurgy is founded on the original application of it by Mr. Spencer. As already stated, he covered metal plates with wax, and after scratching through the coating, and exposing the metal, he submitted the plate to voltaic action in a solution of sulphate of copper, and thus obtained a representation, in relief, of the figures cut through the wax; but he does not seem to have thought of the application of this mode of deposition, since adopted, by which engravings in relief are obtained, and printed from with the ordinary letter-press, in the same manner as woodcuts. The name given to this new art is "Glyphography," and it is used with great advantage when the effect of copper-plate engraving is required; for cross lines, which are difficult to cut in wood, can be worked bythis method with as great facility as in copper-plate etching.
Another application of Electro-Metallurgy that promises to be useful, is the coating of glass and earthenware vessels with copper, so as to enable them to be placed over the fire without being cracked. A glass sauce-pan might thus be made, which, protected by metal covering, would neither break nor crack when placed upon the fire, because the metal would diffuse the heat over the whole surface, and prevent the unequal expansion of the vessel, which is the cause of the cracking of glass and earthenware when placed upon the fire. A patent was granted last year for a mode of coating earthenware vessels with copper or iron by electro-chemical deposition. The earthenware is first covered either with copper leaf or with bronze powder, to obtain an electrical conducting surface on which the copper can be deposited, and the vessel is then placed in a solution of sulphate of copper, and put in connection with the negative pole of a voltaic battery.
The electrotype is frequently applied with advantage to the preservation and multiplication of objects of art and natural productions, for even the forms of flowers may be in this manner rendered durable; but the most important use that has been made of the process is in plating and gilding. To effect that object, it is necessary to employ a voltaic battery separated from the vessel in which the decomposition takes place. The annexed diagram shows an arrangement of this kind. A single cell of a Daniell's battery,a, is connected by wires from its positive and negative poles, with metal rods placed across the decomposition cell,b. The articles to be plated are suspended by wires from the metal rod,f, and a plate of silver is attached to the rod,e. Thus, when the vessel is filled with the silvering liquid, a voltaic current is established, and the deposition is effected on the articles connected with the negative pole.
The menstruum best adapted for electro-plating is a solution of silver in cyanide of potassium. During the process of deposition, the same quantity of metal that is deposited from the liquid on the objects connected with the negative pole of the battery is restored to it, by dissolving an equal quantity from the silver plate connected with the positive pole, and in this manner the solution is maintained at the same strength. Any thickness of silver may be deposited by continuing the process, but about one ounce and a half to a square foot of surface is considered a full quantity. Those parts on which no silver is required to be deposited are covered with varnish or wax, which protects them from the voltaic action.
Where the operation of electro-plating is carried on extensively, decomposing troughs, holding nearly 300 gallons, are employed, and the silver plates in a single trough expose a surface of thirty square feet to the dissolving action of the menstruum under the influence of the voltaic battery.
By the aid of electro-plating the most elaborate designs of the artist in metal can be covered with silver on every part; and a group, finely engraved in copper, may be made to resemble in every particular a work cut out of solid silver. The metal is usually deposited in a granulated state, resembling "frosted" silver, and the parts required to be bright are subsequently burnished; but by the addition of a few drops of the sulphuret of carbon to the solution, the silver may be precipitated perfectly bright.
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 and6 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-lightworks.9
Though the production of illuminating gas from natural sources had been thus long known, the idea ofdistilling 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 inventionof the first plan of a steam locomotiveengine.10He 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 3,000candles.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 publiccompany 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 followingspecimen:—
"Must Britons be condemned for ever to wallowIn 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."
"Must Britons be condemned for ever to wallowIn 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."
"Must Britons be condemned for ever to wallowIn 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 theChemical 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 thisaddress:—
"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 diffusepost obitlight.Perhaps, translated to another sphere,Thy spirit—like thy light, refined and clear—Ballooned with purest hydrogen, shall rise,And add aPATENT PLANETto the skies.Then some sage Sidrophel, with Herschel eye,The brightWinsorium Sidusshall descry;TheVox Stellarumshall record thy name,And thine outlive another Winsor's fame."
"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 diffusepost obitlight.Perhaps, translated to another sphere,Thy spirit—like thy light, refined and clear—Ballooned with purest hydrogen, shall rise,And add aPATENT PLANETto the skies.Then some sage Sidrophel, with Herschel eye,The brightWinsorium Sidusshall descry;TheVox Stellarumshall record thy name,And thine outlive another Winsor's fame."
"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 diffusepost obitlight.Perhaps, translated to another sphere,Thy spirit—like thy light, refined and clear—Ballooned with purest hydrogen, shall rise,And add aPATENT PLANETto the skies.Then some sage Sidrophel, with Herschel eye,The brightWinsorium Sidusshall descry;TheVox Stellarumshall record thy name,And thine outlive another Winsor's fame."
"Though we may smile at Mr. Winsor's extravagant plans and calculations," observes theJournal 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; norwere 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 purehydrogen.12The best kind of gas for illumination isobtained 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.
Therationaleof 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 clayretorts, 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 projectingthrough 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 accompanyingwoodcut. 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 thencepasses 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 spermaceticandles.13The 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, whichadmits 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 escapeof 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 lettersc,c. Inside it there revolves another cylinder, made also of thin sheet iron, and divided into four compartments, markedd,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 ati.
The action of the instrument will be readily understoodby 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 areliable 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, asoriginally 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.
The Electric Light is the brightest meteor that has flashed across the horizon of promise during the present century. When first exhibited as a means of illumination, about twelve years ago, the splendour of the rays emitted, and the delusive representations of the small cost required to produce such a brilliant light, led the public to believe that the career of gas-lighting was drawing to a close, and that night would be turned into day by this wonderful demonstration of electrical power. The light produced by charcoal points, subjected to the action of a powerful voltaic battery, was, however, no novelty at that time; for as far back as 1810, Sir Humphry Davy was accustomed to exhibit that development of electrical force at the Royal Institution, and it formed a standard experiment in most chemical lectures. But it seems not to have been thought applicable in those days to the purposes of illumination; and when Mr. Staite brought it into notice, and exhibited its effects on the tops of some public buildings, it was considered one of the most wonderful inventions of the age.
Mr. Staite's patent, taken out in 1847, though commonly supposed to be for the Electric Lightgenerally, was limited in its clauses to the construction of a voltaic battery and apparatus, adapted for maintaining constancy, and for giving steadiness to the light. The merely temporary continuance of thevoltaic arc, as it was formerly called, seemed indeed to preclude the possibility of its adoption as a means of illumination; it was therefore a great point gained to give stability and constancy to the light. The difficulty of accomplishing this will be perceived when it is known that the charcoal points, between which the action takes place, are constantly undergoing change, the particles of carbon being transferred from one to the other. There is no actual combustion of the charcoal, in the ordinary meaning of the term; the action is principally confined to the transfer of the charcoal connected with the positive pole, to that connected with the negative pole of the voltaic battery, a hollow being formed in one, and a pyramidical accumulation of particles in the other. This action was beautifully shown by Professor Faraday at the Royal Institution last year, by projecting the image of the charcoal points on to a screen, by means of the Electric Light itself. The image, magnified by the lenses of the electric lamp, could thus be distinctly seen without being too brilliant to dazzle the eyes. The particles of carbon, heated to whiteness, were perceived to be in active motion, and the piling up of the pyramid in one, and the hollow produced in the other, were continually varying the distances between them, and thus tending to cause unsteadiness in the light.
Numerous contrivances have been adopted for the purpose of keeping the points at exactly the same distance, as the want of stability was supposed to be the only obstacle to the adoption of the Electric Light. These contrivances have so far succeeded, that a tolerably steady light can be maintained for some time, but under the most careful management the points occasionally approach too near or are too far apart to maintain an equable light.
Among other inventions to increase the steadiness of the light is one that was patented in 1856, by Mr. Way, in which mercury is substituted for charcoal, but the steadiness of light to be thus acquired must be attained with a great loss of illuminating power, and the vapour arising from the combustion of the mercury would be extremely injurious to health.
Mr. Hearder, of Plymouth, has produced more brilliant effects with the Electric Light than any other person. Some remarkable exhibitions of the power of the light were made by him, in April, 1849, from the top of the Devonport Column, and several scientific gentlemen undertook to make observations at different localities to a distance of five miles. At Tremeton Castle, on the banks of the Tamar, a distance of nearly 3½ miles; the light cast a strong shadow, and writing could be distinctly read by it. The space illuminated was at least three quarters of a mile broad. To aid the effect, a reflector was employed, and when the rays were directed to the clouds, they had the appearance of a huge comet, the reflector being the nucleus. The intensity of thelight was ascertained to be equal to that of 301,400 mould candles of six to the pound, whilst the light of the Breakwater Lighthouse was equal to only 150 candles. At a distance of five miles the light was sufficiently powerful to enable persons to read a book.
The battery employed by Mr. Hearder in these brilliant experiments consisted of 80 cells of a Maynooth battery, 4 inches square, and the carbon cylinders between which the light appeared were formed of powdered coke, mixed with tar, and rammed into a tube three quarters of an inch in diameter. When these cylinders are about a quarter of an inch apart, the Electric Light appears at the end of each for the space of more than half an inch. The light, during the experiments at Plymouth, was maintained for three hours, and the materials employed amounted to one pound and a-half of zinc, 114 fluid ounces of sulphuric acid, the same quantity of nitric acid, and six pounds of muriate ofammonia.14
The most serious practical objection to the introductionof the Electric Light, as a means of general illumination, is its expense. When the project was first brought into notice, attempts were made to show that the battery power required might be obtained at little cost, and in this respect some deceptions were practised not creditable to the parties engaged in promoting the scheme. It has been proved by Mr. Grove that the cost of ordinary batteries necessary to maintain the light in full brilliancy would greatly exceed the price of an equal light from gas.
A plan was patented for generating the required voltaic power, free from cost, by applying the residual sulphate of zinc as paint, and an Electric Power and Light Company was formed to carry out the project. But the plan failed, and the affairs of the company have recently been "wound up."
Until some cheaper mode of generating electricity than is at present known be invented, there is no hope of the Electric Light becoming generally available, but there are special circumstances in which it may be applied with advantage. It is peculiarly applicable for lighthouses, as its rays would penetrate through a foggy atmosphere that would obscure the light of ordinary flames, and in such cases the extra cost should not operate as an obstacle to its use.
Those who are not old enough to remember the time when flint-and-steel were the implements employed to obtain a light, can have no sufficient appreciation of the great convenience of "Lucifer" matches. In those "good old times," it was a regular household care to provide a sufficiency of tinder, to see that it was kept dry, and that there was a proper flint "with fire in it." The striking of a light, when the tinder-box was adequately supplied, was no mean accomplishment; and the unskilful hand, operating in the dark, would either get no sparks at all, or send them in a wrong direction, and not unfrequently strike the skin off the knuckles, in the vain endeavour to set light to the tinder. Or if the tinder were damp, the sparks would fall upon it without igniting, and minutes would be spent in holding a pointed brimstone match to the delusive spark, and blowing at it without effect. Sometimes the incautious operator, tired with his fruitless efforts, would sprinkle gunpowder over the tinder, to make it take fire more readily, and whilst puffing at a long-desired spark, the gunpowder would explode in his face and nearlyblind him. Such were some of the annoyances, attended by loss of time, that were experienced in obtaining the same result that is now produced instantaneously, and much more effectively, by merely rubbing the match against any rough surface.
Several attempts had, indeed, been made many years ago to supplant the flint-and-steel and tinder-box, and some of the plans adopted so closely approach the matches now in use, that we wonder the inventors did not succeed long since in contriving the very facile means of striking a light that we now enjoy. Phosphorus and brimstone matches were first employed for the purpose. The phosphorus was contained in a bottle placed within a tin case, which also held the pointed brimstone matches and a piece of cork. The match was dipped into the phosphorus bottle, and then rubbed on the cork; and the friction excited sufficient heat to inflame the small quantity of phosphorus adhering to the match and, to set fire to the sulphur. These phosphorus boxes answered the purpose very well, but the apprehended danger of using so inflammable a substance prevented their coming into general use; and they were much more costly than a tinder-box.
In the next advance, if it may be so called, in the invention of instantaneous light-producers, phosphorus was altogether discarded, and a mixture of chlorate of potass, then called oxymuriate of potass, and sugar was employed. Those substances, when combined, inflame explosively in contact with sulphuric acid. In applying them for the purpose ofobtaining instantaneous light, they were mixed together in an adhesive menstruum, into which the ends of small rectangular matches were dipped. These matches very nearly resembled the "Lucifers" of the present day. To ignite them, a small bottle containing sulphuric acid and asbestos was provided, and they were arranged together in an ornamental taper-stand for the chimney-piece. This apparatus was not received with much favour, partly on account of injury done by a careless use of the sulphuric acid, partly because it failed to act when the acid had absorbed moisture from the atmosphere, but principally because of its cost.
To obviate the objection arising from the use of sulphuric acid in open bottles, an ingenious contrivance was adopted, by which each match contained its own reservoir of acid sufficient for igniting the inflammable compound. Small glass globules, containing sulphuric acid, were introduced into the composition of chlorate of potass and sugar, which, when broken, set fire to the mixture and lighted the match. These instantaneous lights, which were calledPrometheans, were more ingenious than useful, because the trouble of manufacture rendered them expensive, and the sulphuric acid was more likely to injure furniture in that form than when a bottle with asbestos was used. The Prometheans, however, possessed the advantage of portability, and for occasional purposes they were convenient. In some of the forms in which the Prometheans were manufactured, the glass globule of acid, surrounded by its inflammable compound,was attached to the end of a small stick of sealing-wax, sufficiently large to seal a letter; but this refinement in instantaneous lights was not much patronized.
Notwithstanding these ingenious attempts to produce light by chemical action, the flint-and-steel retained possession of the field until a match was made that ignited by friction alone. The first kind of friction match was invented in 1832. It consisted of a thin splinter of dried wood, the top of which was dipped in a mixture of one part of chlorate of potass, two of sulphide of antimony, and one of gum. To ignite the match it was necessary to draw it briskly through sand-paper. These matches required some address to light them, because much more friction was required than is sufficient to light Lucifers.
The next improvement was the "Congreve" match, in which recourse was had to the materials previously used, separately, for obtaining instantaneous lights. Congreve matches were composed of an emulsion of phosphorus mixed with chlorate of potass, into which the matches, previously tipped with sulphur, were dipped. These matches were of the same size and form as the Lucifers now in general use, and they ignited readily by friction on sand-paper or other rough surface. Their explosive noise on inflammation, which gave them their name, was the only apparent difference between Congreves and Lucifers, and their introduction completely supplanted the flint-and-steel.
The noiseless match, or Lucifer, has, in its turn,driven the Congreve almost out of use, though for practical purposes the latter was as effective, and it was less dangerous. The Lucifer matches depend altogether on phosphorus for their inflammability. Their composition is an emulsion of phosphorus with glue, nitre, and some colouring matters. The sulphur matches, after having been tipped with that composition, are exposed in a warm room until a sufficient quantity of the phosphorus is evaporated by slow combustion, to leave a film of glue on the surface to protect the remainder from the action of the atmosphere. The usual proportions for the compound are, phosphorus four parts, nitre ten, glue six, red ochre five, and smalt two. The principle on which the action of Lucifer matches depends, is the strong affinity of phosphorus for oxygen, of which the nitre with which it is mixed contains an abundant supply; and by drawing the match across sand-paper, sufficient heat is excited by the friction to ignite the phosphorus, and the nitre supplies the oxygen to maintain rapid combustion.
The manufacture of Lucifer matches is conducted on a very large scale in this country and on the Continent. It requires several ship loads of wood to supply the requirements of Lucifer-match makers; and ingenious contrivances have been patented for cutting it up into splints of the proper size. For that purpose, after the wood has been reduced to the required lengths by circular saws, it is cut up into splints by a number of lancet points, separated from each other as far apart as the thickness of a match, which passover the wood and divide it with great rapidity. The splints are collected into bundles of one thousand, and each end having been dipped into melted sulphur, they are divided in the middle by a circular saw.
The Reports of the Juries of the Great Exhibition supply a variety of statistical details respecting the manufacture of chemical matches, from which it appears that the quantity made in Austria, in 1849, amounted to 50,000 cwt.; and that in France, in 1850, the phosphorus consumed in the manufacture of matches, amounted yearly to 590 cwt.; and the consumption has rapidly increased since that time. In this country, it is calculated that eight tons of phosphorus are yearly used in making matches, the number of which is stated to be 40,000,000 a day. Large quantities are also imported from Germany, where they are manufactured so cheaply, that fifty boxes each containing 100 matches, are sold for fourpence.
The latest improvement in chemical matches is the "Vesta," which consists of small wax, or stearine tapers, with an igniting composition at the end, consisting of chlorate of potass and phosphorus. These Instantaneous Lights are made without sulphur, consequently the disagreeable smell of the common Lucifer is avoided. The convenience of smokers has also been consulted in the manufacture of Instantaneous Lights. The fusees, now so frequently used for lighting cigars, are composed of thin card-board cut half through, steeped in nitre and with a small quantity of phosphorus; and the tearing of the paperacross produces sufficient heat to ignite the inflammable card.
Thousands of persons, principally children, are now employed in the manufacture of chemical matches. The occupation, as at present conducted, is very unhealthy, for the fumes of the phosphorus produce a disease of a remarkable kind in the jaw-bone, which often proves fatal. No cure has yet been found for this peculiar disease, occasioned by the phosphorus in the state in which it is commonly used. A preparation of that substance has, however, been made which may be used without injury, and which possesses the advantage also of being less dangerously inflammable; but as the redamorphous phosphorus, as it is called, is rather more costly, the manufacturers of Lucifer matches object to use it.