PART II.

[1]A Statement of the advantages to be derived from coal gas.—p. 42.

It remains further to be observed that the coal, by yielding gas and other products, namely, tar, pitch, and ammoniacal liquor, is not entirely lost. It produces, besides light, an excellent fuel, namely, coke; and as a manufactory, or workshop, generally requires heating as well as lighting, there is a gain both ways. The manufacturer, by distilling his coal instead of burning it as it comes from the pit, saves his candles and improves his fuel. One effort at the outset in erecting a gas apparatus, will reduce his annual disbursement for those two articles of prime necessity, much in the same manner, though in a greater degree, as the farmer gains by building a thrashing machine and laying aside the use of the flail.

The coal is so far from being reduced in consequence of the gas-light process, to an useless mass, that in many places immense quantities are reduced to the state of coke for the purpose of renderingthe coal a better fuel than it was in its natural state; for coke gives a strong and lasting heat. It is equally valuable for kitchen and parlour fires, and still more as a necessary requisite in some important branches of manufacture, so that in whatever quantity coke may be produced, it can never want a good market. The demand for coke in this capital, since the establishment of the gas-light works, has prodigiously increased. Numerous taverns, offices, and public establishments, which heretofore burnt coal, now use coke to the total exclusion of coal; and in almost every manufactory, which requires both extensive lighting and heating, gas and coke are now the means jointly employed. A coke fire emits a very uniform and intense heat; it produces no sparks, and burns free from soot and smoke; it requires no trouble in managing, and to those who have the misfortune of being plagued with a smoaky chimney, affords the only certain cure.

Another valuable product is the tar which is deposited during the production of the gas, this tar when rectified by a slight evaporation, has become an article of commerce. Large establishments,both of coal tar, coal oil, and pitch, are in full action, and the commodities which they furnish have become in great demand. The ammoniacal liquor which the gas-light process affords, has of late given rise to very important branches of chemical manufacture, carried on upon a large scale. But as the gas is at present supposed to be the only object in view, for the sake of the light which it yields, the other products being only accidentally connected with its extraction, let us leave the idea of profit on them out of the question, and with the utmost latitude of concession, require them only to stand as in part for a portion of the coal employed in the process, we have still the gas, an article which performs the functions of the oil, the tallow, or the wax for which it is substituted; and to the price of which we have no need to call the attention of those who make use of them. There remains only to be opposed on the other side, the expence of the apparatus by which the gas is to be prepared, and the lights maintained. From the materials and the workmanship, with the interest of the capital sunk, the expence in the first instance, must be very considerable. Butwhere the quantity of light must be great, even from cheap substances, or where, with a less quantity of light, the substances from which it is derived must be of the costliest kind; such is in either case the enormous expence of these materials, that by superseding them and making every reasonable allowance to the engineer who erects the gas apparatus, the sum it costs, both principal and interest, is soon liquidated, leaving at last a total saving, excepting the expence of accidental repairs, which, from the durability of the materials employed, seldom exceeds a trifling sum.

The principal expence in the pursuit of this new branch of civil and domestic economy, is therefore, the dead capital employed in erecting the machinery for obtaining and conveying the gas. The floating capital, after the first cost incurred in erecting the apparatus, is comparatively small; even if usurious interest is allowed for the first cost of the apparatus, and its deterioration, the saving must always be considerable, especially if the number of lights furnished are comparatively in a small place.

At the same time were we to offer advice to the public on this subject, it would be, that no private individual resident in London, should attempt to light his premises, for the sake of economy, with coal gas by means of his own apparatus, whose annual expence for light does not exceed forty pounds. But when a street, or small neighbourhood is required to be lighted the operation may be commenced with safety; the sum required for erecting the apparatus, and the labour attending the process, together with the interest of money sunk, will then soon be liquidated by the light and other products.

Individuals have accordingly engaged successfully in the distillation of coal, and trade with advantage in the articles produced by the process.

In like manner may the lighting of cities be accomplished without the aid of incorporated bodies; and parishes may be lighted by almost as many individuals as there are streets in a parish.

The supplying of light to the street or parish lamps alone, of any district of street lamps only, can never be undertaken with economy in thiscapital, nor indeed in any other; for the money sunk in furnishing the mains or pipes only, must always greatly exceed what any revenue from the lighting of the streets alone can compensate.

The most beneficial application of gas-lights unquestionably is in all those situations where a great quantity of light is wanted in a small place; and where light is required to be most diffused, the profit of this mode of illumination is the least. Hence, the lighting of the parish, or street-lamps alone, without lighting shops or houses, can never be done with economy.

It may be objected to the universality of our conclusion that the price of coal differing very much in different places will occasion a variation in the expence of the new mode of lighting.

The price of coals can however have but little effect upon the cost of the gas-lights; because the very refuse, or small coal, which pass through the screen at the pit’s mouth, and which cannot be brought into the market, nay, even the sweepings of the pit, which are thrown away, may be employed for the production of coal-gas. It makes no difference in what form the coal is used. Thiscircumstance may contribute to enable coal-merchants to furnish coals in larger masses, and as they come from the mine, instead of increasing the bulk by breaking them into a smaller size, which is a practice commonly followed.

The demand which the gas-light occasions for inferior sorts of coal may hereafter contribute to lower the price of the superior kinds, and keep a level which cannot be shaken under any circumstances. It may contribute to prevent combinations which do certainly operate to the prejudice of the public, and sometimes put this great town at the mercy of a few proprietors in the north, who deal out this commodity in any way they please. The competition thus produced, it is impossible not to consider as an advantage, which would tend to prevent such combinations, and put the inhabitants of London out of the reach of them.

The advantages which the coal trade must reap from the introduction of the gas-light must be very considerable. There is already less waste, but a greater consumption of coal than formerly. The lower classes of the community are scantily supplied with firing; and nothing but a reduction ofprice is necessary to increase to a very large amount the average quantity of fuel consumed in the country. The lightness of the coke produced by the gas-light manufacture diminishing the expence of land carriage, facilitates its general diffusion—the comforts of the poor are becoming materially augmented, and a number of useful operations in agriculture and the arts are beginning to be carried on, which have been hitherto checked by the extravagant price of fuel. If any additional vent were wanted for the coke, it would readily be found in the continental market; coke being better suited than coal to the habits of most European nations.

Many, and unquestionable as are the advantages of this new mode of procuring and distributing light, it was not to be expected that an invention which went to impair a branch of trade, in which a large portion of skill and capital had hitherto been successfully employed should escape encountering very considerable opposition. On the first introduction of the gas-lights, great but happily unsuccessful endeavours were made to alarm the public mind by dismal forebodings of the destructionwhich would ensue to the Greenland trade, and the consequent loss of a valuable nursery of British Seamen. When impartially considered it will be found that there was nothing more in this objection than the common clamour that is always set up against every new means of abridging labour, to which had the public listened, an interdict would have been laid upon the spinning and threshing machines, the steam engine, and a thousand other improvements in machinery.

Such clamour scarcely ever fails to be made when the extension of machinery, the application of inanimate power, and the abridgment of labour consequent on either, is a matter proposed. We are then sure to be told that the scheme of mechanical or chemical improvement is pointed against the human species, that it tends to drive them out of the system of beneficial employment and that, on the whole, the sum of the improvement is not only a less proportion of good to society, but a positive accession of misery to the unemployed poor.

The misfortune of this argument is that to be good for any thing, it would prove a great dealtoo much. It is not confined in its scope to any particular species or defined extent of improvement, but is equally proscriptive of all improvements whatever. It is a principle for savage life, not for a state of civilization. It takes for its basis that it is an advantage to perpetuate that necessity for hard and incessant labour under which man finds himself originally placed by nature, with all the wants, privations, ignorance and ferocity, which are attendant on that condition, and that every discovery, invention, or improvement which tends to abridge the quantity required of human labour, and to augment the resources for living and enjoyment is a serious injury to society. The advocates of this narrow theory do not go the whole length of maintaining that diminishing labour, and increase of substance, are in themselves positive evils, a position too absurd perhaps for any one to uphold; but they maintain what ends in a consequence nearly as untrue, namely, that neither the one nor the other is of any advantage to society at large. The palpable error of this theory is, that it supposes that all improvements which tend to supersede human labour, arenecessarily made for the benefit of a few, and not for the common benefit of the many; that instead of lessening to each individual the share of labour requisite to obtain the means of his subsistence, their only tendency is to lessen the value of each personas labour, and to oblige him to work more in order to live equally well.

Now, however the existing state of things may be in this country, or in other countries, arising out of a variety of arbitrary circumstances, foreign to the natural, and in all cases the ultimately inevitable course of industry, it is a matter of justice, clear and undeniable, that every improvement in society ought to be the property of the many, and not of a few; and that it ought either to lessen the quantity of labour necessary for acquiring the means of living, or to increase the profit to be gained by continuing the same quantity of labour. Nor does there seem any reason for believing that, in point of fact, the actual distribution of things is so far from according with this principle of justice as some superficial and prejudiced observers are fond of representing. The labourer, or artizan, may now work a greater number of hours dailythan he did years ago; but how seldom do we find this to be the case without his comforts being more than proportionally multiplied, and his ultimate independence from labour essentially promoted. In general, however, the fact is, if we may give credit to well informed economists, that the working classes do not labour more than formerly, and yet live, or at least have the means of living better; and that by working even less than formerly, they can obtain the means of living quite as well.

Let the real state of matters in this respect, however, be as it may, the question comes to be one merely as to the distribution of the produce of nature and of art, and instead of opposing improvements because they tend to encrease that produce, the object of those who have really the good of their fellow-creatures at heart, ought to be, to encourage such improvements as much as possible, but at the same time to obtain a correction of any partiality or injustice which may have crept into the distribution of their beneficial consequences. It is not to be denied that all new improvements which interfere with and change the occupationsand habits of the working classes of people, must at first expose them to inconvenience and distress, against which it is in fairness the duty of society to protect them; but let not that temporary inconvenience and distress which can and ought to be provided against, be held as an insuperable obstacle to the adoption of an improvement the ultimate tendency of which it is to better the condition of mankind.

It is likewise true that the manufacturing classes often suffer great want by the occasional suspension of employment, and sometimes actual oppression, by the demand for labour; but that involves a question more immediately connected with political economy than the present subject.

It is not the machinery that is in fault in such cases, but those speculators who occasion an inordinate excess of employment, or those statesmen who, with their folly, derange the great machine of human interests and intercourse.

Every invention which tends to diminish the labour of men must be a benefit to the species; and it is wicked to argue against the use of any thing from its occasional abuse.

If the application of mechanical inventions thus tends to improve the humanity of the public, if it reduces the necessity of hard labour, and diminishes the danger of many occupations which we contend it does, they who contribute to this object deserve our respect and gratitude.

It may be true that we have now no such minds as those of Homer, or Bacon, or others of their stamp; but we should reflect that the circumstances which produced such characters are gone by, and great faculties have found other objects and other materials to work with.

The use of mechanical industry not only improves and augments the comforts of domestic life, but it also, perhaps, does as much to soften the feelings of mankind towards one another as the precepts of philosophy. It tends to engender a detestation of hard labour, and to make the world consider not what the labourer may be able to do in tasking him, but what he ought to do without detriment to himself. It effects this by withdrawing, to a great degree, from observation, the distressing spectacle of men and animals toiling beyond their strength.

It ought never to be forgotten, that it is to manufactories carried on by machinery, and abridgment of labour, that this country is indebted for her riches, independence, and prominent station among the nations of the world.

Authentic estimates have shewn, that the use of machinery in Great Britain, is equivalent to an addition to the population of upwards ofone hundred millions of adult persons.

This immense accession of power, has enabled this country to withstand assaults, and to achieve objects of political ambition, that appear almost miraculous when compared with the geographical extent and numerical population of the kingdom.

With respect to what has been advanced as to the probable injury that would result from the general adoption of the gas-lights all over the country, to the Greenland trade, it may be observed that the traffic might with more propriety be called a drain than a nursery of the naval force. The nature of the Greenland service requires that the crew should consist of able bodied sailors; and being protected men, not subject to theimpress law, they are rendered useless for national defence. The nursery of British seamen is the coasting trade; and as the gas-light illumination becomes extended it will increase that trade as much as it diminishes the Greenland fishery.

Even on the extreme supposition that it would annihilate the Greenland fisheries altogether, we should have no reason to regret the event. The soundest principles of political economy must condemn the practice of fitting out vessels to navigate the polar seas for oil, if we can extract a superior material for procuring light at a cheaper rate from the produce of our own soil. The consequence of lighting our dwellings and manufactories with gas can in fact prove injurious only to our continental friends, one of whose staple commodities, tallow, we shall then have less occasion to purchase, although the new lights can never supersede entirely the use of candles and moveable lights.

All substances, whether animal, vegetable, or mineral, consisting of carbon, hydrogen, and oxigen, when exposed to a red heat, produce various inflammable elastic fluids, capable of furnishing artificial light.

The gases thus obtained are called carburetted hydrogen; they produce, from their combustion, water and carbonic acid. The species of carburetted hydrogen, procured from pit-coal, has of late been calledcoal gas.

We perceive the evolution of this elastic fluid, during the combustion of coal, in a common fire.The coal, when heated to a certain degree, swells and kindles, and frequently emits remarkably bright streams of flame. And after a certain period these appearances cease, and the coal glows with a red light.

The flame produced from coal, wood, turf, oil, wax, tallow, or other bodies, which are composed of carbon, hydrogen and oxigen, proceeds from the production of carburetted hydrogen gas, evolved from the combustible body when in an ignited state.

It must have been noticed at the same time, that in the common mode of burning coal in a fire-place, or stove, nearly the whole of this inflammable gaseous matter is lost. We often see a flame suddenly burst from the densest smoke, and as suddenly disappear; and if a light be applied to the little jets that issue from the bituminous part of the coal, they will catch fire and burn with a bright flame. The fact is, that the greater part of the carburetted hydrogen gas, capable of affording light and heat, continually escapes up the chimney, during the decomposition of the coal, whilst onlya small part is occasionally ignited, and exhibits the phenomena of the flame.

If coal instead of being burnt in the way now stated, is submitted at a temperature of ignition in close vessels, all its immediate constituent parts may be collected. The bituminous part is melted out in the form of coal tar, there is disengaged at the same time a large quantity of an aqueous fluid, contaminated with a portion of oil, and various ammoniacal salts. A large quantity of carburetted hydrogen, carbonic oxide, carbonic acid, and sulphuretted hydrogen also makes their appearance, and the fixed base of the coal, alone remains behind in the distillatory apparatus, in the form of a carbonaceous substance calledcoke. An analysis of the coal is thus effected by the process of destructive distillation. The products which the coal furnishes may be separately collected in different vessels. The carburetted hydrogen, or coal gas, when freed from the foreign gases may be propelled in streams out of small apertures, which when lighted may serve as a flame of a candle and then form what we now callGas Lights.

It is in this manner that from pitcoal a production of our own soil, we procure a pure, lasting and brilliant light, which in other cases must be derived from materials in part imported from abroad.

In order to apply this mode of procuring light on a large scale as now practised with unparalleled success in this country, the coal is put into vessels called retorts and furnished with pipes connected with reservoirs to receive the distillatory products. The retorts are fixed into a furnace, and heated to redness. The heat developes from the coal the gaseous and liquid products, the latter are deposited into receivers, and the former are conducted through water in which quick lime is diffused by which the carburetted hydrogen gas is purified. The sulphuretted hydrogen and carbonic acid which were mixed with it, become absorbed by the quick-lime, and the pure carburetted hydrogen is stored up in a vessel called the gas-holder, and is then ready for use.

From the reservoir in which the gas has been collected, proceed pipes, which branch out intosmaller ramifications until they terminate at the place where the lights are wanted and the extremities of the branch pipes are furnished with stop-cocks to regulate the flow of the gas into the burners or lamps.

The production of gas-lights, is therefore analogous to that of flame produced from tallow, wax, or oil. All these substances possess, in common with coal, the elements of certain peculiar matters, which are capable of being converted into inflammable elastic fluids by the application of heat.

The capillary tubes, formed by the wick of a candle, or lamp, serve the office of the retorts, placed in the heated furnace in the gas-light process and in which the inflammable gaseous fluid is developed. The wax tallow or oil, is drawn up into these ignited tubes, and is decomposed into carburetted hydrogen gas, and from the combustion of this substance the illumination proceeds. In the lamp as well as in the candle, the oil, or tallow, must therefore be decomposed before they can produce a light, but for this purpose the decomposition of a minute quantity of the materials successively, is sufficient togive a good light. Thus originates the flame of a candle or lamp.

Nothing more therefore is aimed at in the gas-light process, than to separate the immediate products which coal affords, when submitted to a temperature of ignition in a close vessel; to collect these products in separate reservoirs, and to convey one of the products, the inflammable gas, by means of pipes and branching tubes, to any required distance, in order to exhibit it there at the orifice of the conducting tube, so that it may be used as a candle or lamp.

The whole difference between the gigantic process of the gas light operation, and the miniature operation of a candle or lamp, consists in having the distillatory apparatus at the gas-light manufactory, instead of being in the wick of a candle or lamp. In having the crude inflammable matter decomposed previous to the elastic fluid being wanted, and stored up for use, instead of being prepared and consumed as fast as it proceeds from the decomposed oil, wax or tallow; and lastly, in transmitting the gas to any required distance, andigniting it at the burner or lamp of the conducting tube, instead of burning it at the apex of the wick. The principle of the gas-light manufacture is therefore rational, and justifiable by the general mode in which all light is produced.

It only remains to be observed that while the new and important use to which pitcoal may thus be applied, affords a strong confirmation of what has been well observed, that of all subterraneous combustible substances, coal is in this country by far the most important natural production.[2]“It is connected not only with the necessities, comforts and enjoyments of life, but also with the extension of our most important arts, our manufactures, commerce and national riches.

[2]Davy on the Safety Lamp.

“Essential in affording warmth and preparing food, it yields a sort of artificial sunshine and in some measure compensates for the disadvantages of our climate.

“By means of it metallurgical processes are carried on, and the most important materials of civilized life furnished, the agriculturist is supplied with auseful manure and the architect with a necessary cement. Not only manufactories and private houses, but even whole streets and towns are lighted by its application, and in furnishing the elements of activity in the steam-engine, it has given a wonderful impulse to mechanical and chemical ingenuity, diminished to a great extent human labour, and increased in a high degree the strength and wealth of the country.”

We have stated already that pitcoal is in this country the cheapest crude natural production from which carburetted hydrogen gas can be obtained in the large way. It is that which yields it in abundance, and which can with the least trouble and expence be subjected to the operation it has to undergo for the production of the gas.[3]Nature has dealt this mineral out to us, with an unsparing hand, and has provided mines of coal which seem to defy the power of man to exhaust.

[3]Other Substances from which carburetted hydrogen gas, may be economically obtained, are animal and vegetable oil, tar, both vegetable and coal tar; pitch, resin, the essential oils obtainable from vegetable and from coal tar, and the compact species of turf. On this subject we shall speak hereafter.

The principal coal mines in England are those near Newcastle and Whitehaven. The town of Newcastle stands on beds of coal which extend to a considerable distance round the place, and which as far as concerns many hundred generations after us, may be pronounced inexhaustible.

Pitcoal like all other bituminous substances is composed of a fixed carbonaceous base in the state of bitumen, united to a small portion of earthy and saline matter, which constitute the ashes left behind when the coal is burnt. The proportions of these parts differ considerably in different kinds of coal; and according to the prevalence of one or other of them, so the coal is more or less combustible, passing by various shades from the most inflammable coal into blind coal, Kilkenny coal, or stone coal, and lastly into a variety of earthy, or stony substances, which although they are inflammable do not merit the appellation of coal.

All the varieties of coal used in this country for fuel may be divided into the following classes.

The first class comprehends those varieties which are chiefly composed of bitumen only, which take fire easily, and burn briskly with a strong andyellowish white blaze, which do not swell or cake on the fire, and require no stirring, which produce no slag, and by a single combustion are reduced to light white ashes. Some of this species of coal when suddenly heated crackle and split into pieces, especially if laid on the fire in the direction of the cross fracture of their laminæ.

Cannel coal, deserves to be placed at the head of this class; next to this, we may rank all those descriptions of coal known in the London market by the names of Hartley, Cowper’s Main, Tanfield Moor, Eighton Main, Blythe, and Pont Tops. It also includes the sort of coals found in several parts of Scotland, called Splent coal, and some of those raised on the Western Coast of England.

Most of the coals raised in Staffordshire ought likewise to be classed among this species of coal, but the line of distinction between these, and the classes subsequently named, cannot be accurately drawn.

The following table exhibits the maximum quantity of gas obtainable from the first class of coal.[4]

[4]Own Experiments, made at the Royal Mint Gas-Works.

[5]They require a much higher temperature, than is necessary for the decomposition of Newcastle coal.[6]For the maximum quantity of gas produced from this and the three succeeding varieties of coal, I am indebted to J. Gostling, Esq. Proprietor of the Birmingham Gas Works.[7]Most varieties afford a porous, and very friable coke.

[5]They require a much higher temperature, than is necessary for the decomposition of Newcastle coal.

[6]For the maximum quantity of gas produced from this and the three succeeding varieties of coal, I am indebted to J. Gostling, Esq. Proprietor of the Birmingham Gas Works.

[7]Most varieties afford a porous, and very friable coke.

The second class of coal, comprehends all those varieties which contain a less quantity of bitumen, and a larger quantity of carbon than the first class. They burn with a flame less bright and of a more yellowish colour, and the last portion of flame they are capable of yielding is always of a lambent blue colour, they become soft after having laid on the fire for some time, swell in bubbles and pass into a state of semi-fusion, they then cohere and coke, puff up and throw out tubercular scoriæ, with a hissing noise, accompanied with small jets of flame.

In consequence of the agglutination and tumefaction, the passage of air, if this sort of coal be burnt in an open grate, is interrupted, the fire burns as it is called hollow, and would become extinguished if the top of the coal were not from time to time broken into with the poker.

The coke formed from this species of coal is more compact than that produced from the first sort of coal, and is well calculated for standing the blast of bellows in metallurgical operations. In respect to weight the second class of coal is considerably heavier than those of the first class, the differenceamounts to not less than from twenty-eight pounds to thirty-three pounds in the sack of coal. A chaldron of some varieties of this class of coal, if the coals are in large lumps, weighs upwards of twenty-eight hundred weight.

The usual denomination by which the second class of coal is known in the London market, is that ofstrong burning coal. The following varieties are sufficiently known, Russel’s Walls-End; Bewick’s and Craister’s Walls-End; Brown Walls-End, Wellington Main, Temple Main, Heaton Main, Killingsworth Main, Percy Main, Benton Main, and some varieties of the Swansea coal.

The smaller kinds of coal of this class are preferred by smiths, because they stand the blast well. They make a caking fire so as to form a kind of hollow, space or oven, as the workmen call it. Some varieties abound in pyrites, and others are intersected with thin layers of slate and lime-stone. They require more heat for being carbonized than the first class, and the fluid obtained from it by distillation, contains a considerable portion of carbonate, sulphate, and hydrosulphuret of ammonia. They are well calculatedfor the production of coal gas; the coke which they produce is not very brittle, and will bear moving from place to place, without crumbling into dust.

The following table exhibits the maximum quantity of gas obtainable from the second class of coal.[8]

[8]Own Experiments, made at the Royal Mint Gas-Works.

The third and last class of coals includes those which are destitute of bitumen, being chiefly composed of carbon in a peculiar state of aggregation, evidently combined chemically with much earthy matter. Coals of this class require a still higher temperature to become ignited than any of the former classes, they emit little or no smoke. When laid on a fire they burn away with a feeble lambent flame, indeed some varieties give no flame at all, but burn merely with a red glow, somewhat like charcoal, and at length become consumed without caking. They leave a small portion of heavy ashes.

When submitted to distillation they afford little or no tar; of a consistence almost resembling pitch, and a gaseous fluid chiefly composed of gaseous oxide carbon and hydrogen gas. It is scarcely necessary to add that they are altogether unfit to be employed for the manufacture of coal gas. The Kilkenny, Welch, and stone or hard coal belong to this class. They require a strong draught when burnt in an open fire-grate, and the large quantity of gaseous oxide of carbon which they furnish during their combustion is extremely offensive.This is particularly the case with Kilkenny coal. The Welch stone or hard coal is better adapted for culinary purposes, and there is reason to believe that this species of coal might be rendered useful in the smelting of iron ore, by a slight modification in the metallurgic process employed for extracting the metal from its ore, but to eradicate prejudice, and to alter established practices is a work which nothing but time can effect. This species of coal is sent all over the kingdom; it is well calculated for the operations of drying malt and hops, and its small coal or culm has been found a more economical fuel, than Newcastle and Sunderland coals, for the burning of lime and bricks, and for all other processes where no blazing fuel is required.

The following table exhibits the maximum quantity of gas obtainable from this class of coals.

[9]The coal for these Experiments was supplied gratuitously, to the Gas Works of the Royal Mint, by Sir W. Paxton of Middleton Hall.

When we consider the before mentioned varieties of coal in an economical point of view, as fuel to be used in the gas-light process, for heating the retorts, it appears from a series of experiments that have been made under my direction, that the second class of coal comprehending those varieties which contain a larger quantity of carbon than bitumen (p. 45,) afford the most economical fuel, they act less on the grate bars, and fire bricks of the furnace than those varieties which take fire easily and burn briskly with a strong blaze. A mixture of Welch Stone coal, and Newcastle coal forms an excellent economical fuel, where an intense glowing fire is required.

The proper mode of constructing the retorts in which the coal is distilled, and the art of applying them form an object of primary importance in every gas-light establishment. According as the manufacture is conducted in these respects with a due regard to physical principles, depends the quantity of gas which can be obtained in any given time, from any given quantity of coal, the consumption of fuel requisite for the production of that quantity of gas, the degree of deterioration to which the distillatory vessel is subjected, the quality in some measure, of the gas itself; and, as the ultimate result of all these circumstances, the cheapness at which the gas light can be furnished to the consumer.

The essential influence of these various particulars on the value of the art of lighting with coal gas, has led to much assiduous enquiry to ascertain that sort of construction and mode of operation in respect to each of them which may be most advantageous. And in no branch of the new art of procuring light, has a greater variety of plans of improvement been submitted to the several directing boards of gas works, or more labour and expence been incurred in experiments conducted on a large scale, to ascertain the relative merits of these plans. Nor is there any part of the gas-light process in which a greater number of material alterations have been put in practice.

In the earlier periods of lighting with coal gas the retorts employed at some of the gas-light establishments in the metropolis, were hollow cast-iron cones from six to seven feet in length. The greatest diameter of the cone which formed the mouth of the retort, measured from twelve to fifteen inches, and its smallest diameter at the vertex from nine to ten inches.

At other gas works the form of the retort was a parallelopiped from six to seven feet long, thehorizontal, and vertical sides were respectively to each other, as 20 to 15 inches. The angles of these retorts were slightly rounded. Fig. 16,plate V.exhibits a vertical section of this retort.

Again at other establishments semi-cylindrical retorts, placed horizontally upon their flat surfaces were employed; fig. 18.pl. V.The length of these retorts was from five to six feet, and their vertical and horizontal diameters were to each other as 6 inches, to 18 inches. And at a few establishments, ellipsoidal retorts, fig. 17,plate V.were used; these measured from five feet and a half, to six feet in length, their major and minor axes bore different proportions to each other at different establishments. At the first adoption of these retorts, the proportions varied but little from the cylinder, but subsequently the difference between the major and minor axes became gradually increased till at last the major axis has become to the minor axis, as 20 to 10 inches, and at some gas works the proportions are as 25 to 10 inches.

With vessels of these forms the distillatory process was carried on for some years, and the quantity of fuel employed to decompose a given quantity ofcoal by means of them, amounted to from thirty to thirty-six per cent.

When the dimensions of the retorts were increased, both the quantity of fuel and time required for the decomposition of a given quantity of coal was in a far greater ratio; and the operations of charging and discharging the retorts, very troublesome.

Retorts of smaller dimensions have likewise been tried, but the more frequent charging and discharging, which they require, occasioned such a waste of time and labour, and such intermissions, in the temperature necessary for the process of distillation, (besides being attended with other disadvantages which will be afterwards explained), that they were speedily discontinued at the gas works where they had been adopted.

The use of conical retorts, as well as of those of a semi-cylindrical and parallelopipedal form, has of late been discontinued in most establishments. The conical shape not only diminishes the capacity of the vessel, but also renders it incapable of being heated economically.

From two comparative series of operationsmade on a large scale, and continued for upwards of six months with conical and cylindrical retorts, with a view to determine the comparative power of these vessels, it has been proved that the same quantity of gas which can be obtained by means of forty conical retorts, may be procured in the same time and with the same quantity of coal and fuel, by means of thirty-four cylindrical retorts.[10]

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