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Pl. II.
Accums’, Description of Gas Works.
to Face Title.

Mulholland Del^t. W. Read, Sculp^t. Maiden Lane, Covent Garden.

Gas Light Apparatus,
Erected by Order of Government at THE ROYAL MINT, by Fredc^k. Accum.

[Larger plate]

DESCRIPTION
OF
THE PROCESS OF MANUFACTURING
COAL GAS,
FOR THE LIGHTING OF STREETS HOUSES, AND PUBLIC BUILDINGS,
WITH
ELEVATIONS, SECTIONS, AND PLANS
OF THE MOST IMPROVED SORTS OF APPARATUS
NOW EMPLOYED AT THE
Gas Works in London,
AND THE PRINCIPAL PROVINCIAL TOWNS OF GREAT BRITAIN;
Accompanied with comparative Estimates, exhibiting the most Economical
Mode of procuring this species of Light.

WITH SEVEN PLATES.

By FREDRICK ACCUM,
OPERATIVE CHEMIST,

Lecturer on Practical Chemistry, on Mineralogy, and on Chemistry applied to the Arts and Manufactures; Member o£ the Royal Irish Academy, Fellow of the Limnæan Society, Member of the Royal Academy of Sciences of Berlin, &c. &c.

London.

PRINTED FOR THOMAS BOYS. N^o. 7. LUDGATE-HILL. (FROM N^o. 3, PATERNOSTER ROW)

MDCCCXIX.

[Larger plate]

PREFACE.

Compton Street, Soho.

The extraordinarily rapid progress which the recent invention of lighting with coal gas has made in this country, is perhaps without a parallel in the history of the useful arts.

It was an invention not exempted from the misfortune common to all innovations on established practises, of encountering opposition, but it had the fortune common to few, of obtaining an almost instantaneous triumph.

A single exhibition of the gas lights in actual use was sufficient to determine the public judgment in favour of the new mode of illumination; to see was in this case, indeed to believe.

The legislature responsive to the popular voice, and fortified in its responsibility, by the results of special enquiries which were ordered to be made into the merits of the invention, and in which I had the good fortune to be professionally engaged, gave the most liberal and decided encouragement to its adoption.

Capital, often wanting even in this opulent country for undertakings of magnitude, came to the promotion of the new art of procuring and distributing light in overflowing abundance; and already ere many years are elapsed, such has been the rapidity with which the gas light illumination has advanced, that there is not a city and scarcely a town of any note in Great Britain, in which the art of lighting by means of gas, has not been carried into effect, or in which active measures are not in progress, to participate in the benefit of this important discovery.

When the art was yet in its infancy, I published a Treatise, containing a description of the apparatus and machinery best calculated for illuminating streets, houses, and public buildings, by means of coal gas, with remarks on the utility, safety, and general nature of this new branch of domestic economy, as far as then understood, and practised in the metropolis.

The universal avidity for information on the subject, more perhaps than any particular merit in the work itself, produced a demand in this country for four large impressions of this work, in the course of a few years, and I have also had the satisfaction of finding that the Treatise has been translated into the French, German, and Italian languages.

Since this work was written, however, the art of manufacturing and applying coal gas, has undergone so many material improvements, all combining to bring it to a degree of simplicity, precision, and economy, far surpassing every thing which the original mode of practice exhibited, that I have felt I should be guilty of an injustice to the constant demand which still exists for my former Treatise, had I not made it my duty to publish the work I now present to the reader; superseding altogether the former publication, but superseding it from circumstances of necessity, and with a view to good, which I trust will be found not illusory.

The present treatise, as its title expresses, is intended to exhibit the superior process of manufacturing coal gas now employed in the metropolis and the provincial towns of Great Britain, and to lay before the reader the elevations, sections, and plans of the improved Gas Light machinery, which has stood the test of practice, and is now in action at the most celebrated Gas Light Establishments.

In the [first] and [second part] of the Treatise, I have, as introductory to the rest, given a sketch of the chemical theory and production of Gas Light. I have pointed out the leading objects of public and private utility, to which the art of lighting with gas has been, or remains to be applied: and added such other facts and observations as may serve to remove all doubt in the minds of the reader as to the important benefit which this country in particular, and the world at large, have gained by this discovery.

In the [third part] I have stated the maximum quantities of gas obtainable in the large way, from different kinds of coal.

In the [fourth part], I have given a description of all the various forms and dimensions which the distillatory vessels or retorts have successively assumed, as well as of the improvements that have been made in the mode of setting the retorts, with a view to saving them from undue deterioration, and preventing any improvident waste of fuel. I have here given a particular account of the distillatory apparatus now used at the most celebrated gas works in the metropolis.

The [fifth] and [sixth parts], lead the reader considerably further into a knowledge of the economy and practice of this art. They contain an account of a great variety of experiments which have been pursued on a large scale, in order to ascertain the most profitable mode of employing the retorts, the differences of opinion which have existed among practical men with respect to the degree of temperature fittest to be applied, and the number of hours at a time during which the retorts may most advantageously be kept in action, with the particular results which the experiments instituted into these points have afforded; and such other data, as will enable the reader to adopt that mode of operation, which under every circumstance of locality will be found most advantageous.

The changes which have taken place with respect to the retorts, have been before detailed in [part fourth]; but in order to give the manufacturer a nearer insight into the superior advantages attending retorts of the construction lately brought into use, I have given in [part seventh], a detailed description of the horizontal rotary retorts, the application of which has led to a more economical, expeditious, and easy method of manufacturing coal gas than heretofore practised. I have distinctly pointed out the advantages which these retorts present, the particular results they afford, and the method of applying them.

The purification of coal gas forms the subject of [part eighth]. I have compared here, the apparatus for purifying coal gas, as it was originally constructed, with the improved machinery lately adopted, showing the inefficacy and defects of the former, and the decided superiority which belongs to the latter.

The [ninth part] gives an account of the various improved gas holders which have been invented, and now are in action at the most recent establishments, for the purpose of storing large quantities of gas. The improvements that have been made in this department of the Gas Light machinery, are particularly valuable and have contributed more perhaps than any other, to lessen the expence of manufacturing gas for commercial purposes.

In the [tenth part], I have given a description of an entirely new machine, called the gas-metre, or self-acting guage, lately adopted at the Birmingham, Chester, and other gas works, which measures and registers the quantity of gas manufactured in any given time, from any given quantity of coal, or consumed during any period, by any number of burners or lamps. The great services which such a machine must render both to the manufacturer and consumer of gas, are particularly pointed out, and illustrated to the manufacturer, by serving as a complete check on his workmen as to the quantity of work that ought to be performed, and to the consumer, as an exact measure of the quantity of gas he receives, and ought to pay for.

The [eleventh part] is appropriated to the description of another apparatus, called the governor, also of recent invention, and now in use at numerous establishments. The design of this machine is, to regulate the pressure of the gas, before it enters into the mains, the importance of which must be sufficiently manifest. I have also pointed out the application of this apparatus for regulating the magnitude of the flames of gas burners and lamps.

The [twelfth part] treats on gas mains and branch pipes, I have here stated the rules and practical proceedings necessary to be observed, for applying and distributing gas pipes to the greatest advantage.

The most efficient method of introducing the gas to the interior of houses, forms the subject of [part thirteen]. All the necessary instructions are here given to workmen, for adapting the gas pipes, and insuring success at the least cost, under every variety of circumstances.

The [fourteenth part] gives an account of the illuminating power of coal gas—the quantity of gas consumed in a given time, by different kinds of gas burners and lamps, the relative cost of gas, tallow, and oil lights of different intensities, and the most improved method employed for ventilating apartments lighted by gas.

In the [fifteenth] and [sixteenth parts], I have added an account of the manufacture of carburetted hydrogen gas, from coal tar, vegetable tar, and oil, with such other observations as may enable the reader to form a proper estimate of the comparative advantage of manufacturing gas from oil, or tar, under certain circumstances. I have here also given an account of the manufacture of carbonate of ammonia, as now practised, from the ammoniacal liquor obtained in the Gas Light process, and of the manufacture of other saleable products obtainable from coal, namely; pitch, coal tar, and oil.

In conclusion I have to observe that my object throughout has been to make the work a compendium of all the best information which the practice of the art down to the present moment has been able to afford, embodying a great number of data, with which I have been obligingly favoured by gentlemen, the most practically versant in the art, and for which I beg they will individually accept this public expression of my thanks, and obligations, as well as the results which my own labours in this department, neither few, nor inconsiderable have furnished.

To supply the reader with a work of practical utility in a most valuable, and growing branch of national economy has been my object; and I need scarcely add, that the suffrages of the public to the zeal and industry at least with which I have endeavoured to obtain that object, will be a source of infinite satisfaction.

FREDRICK ACCUM.

LONDON, 1819.

CONTENTS.

ADVERTISEMENT.

The author of this work respectfully informs the public, that they may be furnished with estimates, and plans for the building of Gas Works, particularly adapted to the circumstances of the places where they are to be established, and that he proposes to superintend the erection of the works.

Mr. Accum also engages to supply the whole of the Gas Apparatus ready for immediate use, and to guaranty its efficient performance.

Or he will contract with any committee, directory, or public company, for Lighting with Gas, any Town, Manufactory, or Building, upon whatever scale of magnitude, for an annual specific sum.

Of the qualifications for the services which he thus proffers, he would speak with diffidence. Such proofs as he is able to offer of them, are to be found in the work here laid before the reader, beyond which he would add no more than the flattering testimony of approbation, with which his labours have been honoured, in having been selected by His Majesty’s Government to plan and erect the Gas Works at the Royal Mint, and since entrusted with the active management and superintendance of that establishment.

Compton Street, Soho,
May 28, 1819.

The following particulars are required to be stated by those who are desirous of receiving estimates, concerning the comparative economy of applying coal gas as a substitute for oil, wax, or tallow light.

1. A plan of the place to be lighted with Gas, drawn to a scale not less than one tenth of an inch, to ten feet. The design must exhibit the particular spot, where the Machinery is to be erected.

2. The kind of gas lights required, namely; whether the lights shall be equal in illuminating power to one, or more tallow candles of a given weight, or equal to an argand lamp.

3. The number of lights.

4. The average time the lights are to burn, throughout the year.

5. The average price of coal, and rate of workmen’s wages, at the place where the light is wanted.

AN
ACCOUNT
OF THE
PROCESS OF MANUFACTURING
Coal Gas.

PART I.

General Nature and Advantages of the art of procuring Light, by means of Carburetted Hydrogen, or Coal Gas.

The new art of lighting houses, streets and manufactories, with carburetted hydrogen, or coal gas, is one of those modern discoveries on which the admirers of science and the inhabitants of this country in particular, have greater reason to congratulate themselves, than any other invention or discovery of the present age.

This art is so wonderful and important, it speaks so forcibly by the effects it has already produced, that it cannot fail to increase the wealth of the nation by adding to the number of internal resources, as long as coal continues to be dug in this island from the bowels of the earth.

For if we distribute the catalogue of human wants which a civilized state of society has introduced, the production and supply of artificial light, holds next to food, clothing and fuel, the most important place. We might indeed exist without it, but how large a portion of our lives would in that state be condemned to a state little superior in efficacy to that of the animals around us.

If we could for a moment suppose the privation of artificial light, during the absence of the Sun, it would follow as an immediate consequence that the greatest part of the globe on which we dwell, would cease to be the habitation of man. Whether he could ensnare or overtake those animals upon whose unprepared remains he would then be compelled to feed; whether he might store the fruits of the earth for his winter supply—what might be the physical and moral consequences of a state of such desolation, may perhaps be conjectured, but no estimate can show its dreadful magnitude.

How much do our comforts, and how greatly does the extent of our power depend upon the production and supply of artificial light. The flame of a single candle animates a family, every one follows his occupation, and no dread is felt of the darkness of night. It might be a curious speculation to enquire how far, and in what respect, the morals of men would become degraded by the want of this contrivance. But it is sufficient on the present occasion, that, previous to entering upon a dissertation respecting a new art of procuring light, a train of ideas has slightly been hinted at, which cannot fail to show its magnitude and importance.

The progress of the new art of lighting houses, streets and public buildings, by means of the inflammable gas obtainable from coal, has been within these few years uncommonly rapid. The number of gas-lights already in use in the metropolis alone, amounts to upwards of fifty-one thousand. The total lengths of mains in the streets through which the gas is conveyed from the gas-light manufactories into the houses, now measures two hundred and eighty-eight miles.

The gas-light illumination has also spread far and wide through the country. Establishments for the supply of the new lights are carried on at Edinburgh, Glasgow, Liverpool, Bristol, Bath, Cheltenham, Birmingham, Leeds, Manchester, Exeter, Chester, Macclesfield, Preston, Kidderminster, and in many other towns and places of Great Britain.

Every body is now convinced that pitcoal is capable of furnishing light superior to that obtained from oil, wax, or tallow. The public attention is awakened to the new value of coal, and will not rest till the art of lighting with gas is pushed to the utmost of its extent.

In order to arrive at a full and accurate knowledge of the many advantages attending the application of carburetted hydrogen or coal gas, as a substitute for candles or lamps, it may be necessary, especially for the information of those readers who have never personally witnessed this mode of illumination, to take a brief preliminary view of some of the leading objects of public and private utility, to which this mode of procuring and distributing light may be applied, and of the extent to which it is entitled to national encouragement.

The chief advantages attending the use of gas, are superiority and uniformity of light, saving of labour, cleanliness, safety and cheapness.

It must be difficult for a person wholly unacquainted with this art, to imagine with what facility and neatness gas-lights are managed. The gas being collected in a reservoir, is conveyed by means of tubes, which branch out into smaller ramifications, until they terminate at the places where the lights are wanted. The extremities of the branching tubes are furnished with burners, having small apertures out of which the gas issues with a certain velocity corresponding to its degree of pressure. Near the termination of each tube, there is a stopcock, or valve, upon turning which when light is required, the gas instantly flows out in an equable stream. There is no noise at the opening of the valve, no disturbance in the transparency of the atmosphere; the gas instantly bursts on the approach of a lighted taper into a peculiarly brilliant, soft and beautiful flame; it requires no trimming or snuffing to keep the flame of an equal brightness. Like the light of the Sun itself, it only makes itself known by the benefit and pleasure it affords.

The gas flame is entirely free from smell. The gas itself has a disagreeable odour before it is burnt, and so has the vapour of wax, tallow and oil, as it comes from a candle or lamp newly blown out. This concession proves nothing against the flame of gas, which is perfectly inodorous.

The gas-light flame is perfectly steady; a benefit which persons accustomed to read or write by candle-light, are particularly capable of appreciating. With the other modes of illumination we have never the light of the same intensity for two minutes together, independent of that unpleasant dancing unsteady flame which is so harassing to the sight.

The size, form and intensity of the gas flame, are regulated by simply turning the stop-cock which admits the gas to the burner or lamp. The flame may at command be made to burn with an intensity sufficient to illuminate every corner of a room, or so low and dim, as barely to be perceived. It is unnecessary to point out how valuable lights of this description are in nurseries, stables, warehouses, and chambers of the sick. From the facility with which the gas flame can be conveyed in almost any direction, from the diversified size and shape which it can be made to assume, there is no kind of light so well adapted for ornamental illumination.

The flame of coal gas is of a pure white colour, and of a body full and compact. In large masses, it becomes of the same flickering character which is common to all flames of large dimensions, and is owing to the agitation of the surrounding heated atmosphere.

The saving of labour connected with the employment of gas-light, may seem on a small scale to be trifling; but when it is considered that in large manufactories, it is not unusual to find several persons employed for no other purpose than trimming the lamps or setting and snuffing the candles of the establishment, the advantage gained on this head by the use of a species of light which require no sort of attention whatever, cannot but appear very considerable.

The cleanliness of the gas-lights is also a consideration of no small importance, they are attended with none of that spilling of oil, and dropping of grease, which makes the employment of oil-lamps and candles so injurious in many warehouses, shops and private dwellings.

The flame of a gas-light compared in point of brilliancy to that of a candle, is as the flame of a common oil lamp, compared to the flame of a lamp of Argand. The difference between a street, on the night of a general illumination, and any other night when the street is under the dull glimmering light of the ordinary oil lamps, is scarcely more remarkable, than the difference between a street lighted by gas, and one lighted by oil. While the ordinary oil lamps may be said merely to serve the purpose of making “darkness visible,” the gas-lights really dispel the dominion of night, and diffuse a body of light so wide-spreading and intense, as almost to rival the clearest moonshine.

The same brilliancy which makes the gas-lights of such utility out of doors, in lighting the streets, has been found of equal advantage in illuminating the interior of private dwellings, and large public buildings, such as churches, and theatres, &c. From a cluster of gas-lights, fewer by one-half than the number of oil lamps and candles required for lighting up a public edifice of this description in the most ordinary manner, a body of light is furnished which diffuses through the whole, a degree of mellow clearness which is not to be attained by the greatest number of oil lamps, or candles, which a due regard to respiration will admit of being employed. As examples of this, we have only to name the public theatres of the metropolis, all of which are lighted with gas, and in a manner which excites universal admiration.

It may perhaps be imagined that with a substance so inflammable, and amidst the blaze of resplendent flame which produces such beautiful effects, there is a peculiar risk of accidents by fire, but so far is this from being the case, that gas-lights are the safest of all lights. No danger can arise from these lights in any way, but what is common to candle lights and lamps of all kinds, and is the fault of none of them. The gas-lights are in fact a great deal less hazardous. There is no risk of those accidents which often happen from the guttering of candles, from sparks being detached, or from carelessly snuffing them. The gas-light lamps and burners, must necessarily be fixed to one place, and therefore cannot fall or otherwise become deranged, without being immediately extinguished. And further, at any time by shutting the main tube which conveys the gas to the burners and lamps, all the lights in the house can be immediately extinguished. In short, where gas is used, the master of the house, when he has turned the main stop-cock which conveys the gas into the collateral branch pipes, may retire to rest free from any of those apprehensions, which before harassed him, lest a candle might have been left burning, of lest the accidental dropping of a spark might become the cause of enveloping himself and family in destruction.

But the best proof of the great safety of the new lights is, that notwithstanding upwards of fifty-one thousand gas-lamps burn nightly in London, we have not heard of a single accident occasioned by them, though the lamps and burners are generally carelessly managed, while we have too often occasion to lament the effects arising from sparks of candles, or carelessness in snuffing them.

Hence the fire-insurance-offices engage to insure manufactories and public works, at a less premium, where gas is used, than when lighted by other means.

The excessive expence of insurance, arising from the numerous candles employed in most of the first-rate manufacturing establishments, and the combustible nature of the structure of the buildings; the great difficulty of retrieving the injury resulting to a well-organised business, from the accidental destruction of the machinery, are considerations alone sufficient to furnish the strongest economical, as well as political recommendations, for the adoption of the new lights in all manufactories where work is done by candle-light.

We have as yet only adverted to the application of gas in the more ordinary cases where light is wanted, but among other special purposes to which gas-lights may be applied, it would be improper to overlook the peculiarly advantageous use which may be made of them in the supplying of light-houses. From the splendour and distinguishing forms which the gas-light flame is capable of assuming, nothing can possibly be better calculated for such a purpose; and in point of economy, the employment of it would be attended with a saving of at least one half of the ordinary expence of oil lights. By means of a single furnace, as much gas may be produced in three hours, as will furnish during the longest winter night, a flame of greater brilliancy than is now furnished by any lighthouse in Britain, or indeed in the world. The body of flame may be increased to any size, merely by increasing the number of burners; and whatever may be the magnitude of the flame, it will continue to burn, without becoming in the least clouded by smoke, or the reflectors being in the least obscured. Should these considerations lead, as it is to be hoped they will, to the actual employment of gas in the lighthouses around the British islands, it will readily occur, that in proportion as the gas would be found attended with less expense than the present mode of lighting by oil, it would enable the commissioners for light-houses, out of the surplus means which would be thus placed at their disposal, to multiply the number of lighthouses, and thus to add most essentially to the security of British navigation. Nor is it in the case of maritime signal-lights alone, that the use of gas is applicable, by its superior efficacy and cheapness. The saving of expences to the country which would be effected by the substitution of coal gas, for oil and tallow in these and other public establishments, is a consideration which cannot be too much pressed on public attention. The annual expenditure for lighting the barracks of Great Britain alone, is said to fall little short of fifty thousand pounds; for less than one half of which sum, they might be lighted by means of gas much better, and a great deal more safely. Some idea may be formed from the practical saving in this department—how great might be the total saving, were this new mode of lighting adopted in all our national establishments.

In the case of the public arsenals, however, the saving from the employment of coal gas is a consideration of far inferior importance to the superior security attending it. On the preservation of the stores which they contain may depend in a time of war the whole chance of success against the enemy nor can any body who has lived in this country at such a time have forgot the feverish alarm with which the people have frequently seen this security endangered by accidents arising from the use of moveable lights. Were coal gas exclusively employed in such establishments, the fixed position which can be given to the burners, and the absence of all danger from sparks must give a degree of security to those places from fire, far beyond what they at present possess, even when superintended with the greatest possible caution and fidelity.

The same remark is equally applicable to the government offices, public libraries, museums, in short, to all public establishments where the national value of the articles preserved is such that no possible means of increasing their security from destruction should be neglected.

We have now to turn our attention to another general point of view in which the introduction of lighting by gas is not less an object of interest to the public; we allude to the application of gas as a means of heating as well as lighting. Mr. Maiben[1] was the first who directed the attention of the public to this subject; he ascertained that gas from coal gives nearly the same heat when put into combustion, which is yielded by a third part of the coal from which it is extracted. In other words, it has been found that a quantity of fuel giving a particular degree of heat, may be employed so as to produce at the same time another substance yielding nearly an equal degree of heat in a different and more manageable form; a form in which it can be preserved for any length of time, divided into any portions, distributed in any direction, consumed in an open fire-place, or in a stove concealed in any shape; a form in which the flame may issue equally well from iron or from stone-ware, be instantly lighted up and instantly extinguished, be made to burn as long or as short a time as may suit us, and in any degree of intensity between the most animating and brilliant blaze and its total extinction; be extinguished in one room, and the next moment lighted up in any other; in short such a form, that by one proper arrangement from the beginning, with the same portion of fuel, we may at any time have the command of a chearful fire, an adequate and comfortable warmth in any part of our dwelling to which we may have occasion to move, as manageable, and in this way as portable, as the taper by the touch of which it is kindled. To those who have been accustomed to see before them a solid mass of burning fuel, this gas flame may at first have the less satisfactory appearance of a fugitive blaze which we perceive nothing to support. But its uniformity and permanence will soon banish this impression, while it is attended with other advantages not inconsiderable with respect either to comfort or convenience. There are no coals to be carried in, no ashes to be carried out; there is no blowing, no sweeping of cinders, no dust, no interruption of servants; there is no excessive heat in one stage, no sudden damping at another: we have the choice of any temperature, and which we can regulate with the utmost ease. The fire itself is lively and pleasant to the eye: inclosed in transparencies it receives a degree of splendour not easily imagined. Numerous applications of gas, as a source of heat for airing rooms, and other purposes, have already been adopted. It is used in kitchens for keeping meat warm, and for boiling water; in store rooms, in picture galleries, in libraries, for maintaining them at an equal temperature. By copper-plate printers, it is used for warming their plates; and by jewellers and other artists, for soldering.

[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 rendering the 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. But where 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 this capital, 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. This circumstance 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 of price 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 destruction which 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 deal too 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, are necessarily 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 daily than 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 occupations and 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 of one 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 the impress 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.

PART II.

Outline of the new art of procuring light by means of coal gas, and Theory of the production of Gas 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 called coal 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 only a 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 called coke. 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 call Gas 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 into smaller 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 to give 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, and igniting 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 a useful 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.”

PART III.

Classification of Pit-coal, and maximum quantity of gas, obtainable from different kinds of Coal.

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 and yellowish 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.

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 difference amounts 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 of strong 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 calculated for 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.

PART IV.

Form and dimensions of the Retorts originally employed for manufacturing Coal Gas.

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, the horizontal, 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 of coal 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 operations made 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]

[10] These Experiments were made at the commencement of the new art of lighting with gas, at the Westminster Chartered Gas Works, by Messrs. Grant and Hargraves.

Similar experiments have been undertaken, to determine the comparative action of semi-cylindrical and parallelopipedal retorts.[11] The latter, when kept in action day and night, do not long retain their shape; their sides collapse, their capacity becomes diminished, their angular form causes the heat to act upon them unequally, in whatever manner it may be applied, in consequence of which they suffer more deterioration in some parts than in others. Besides, they require a much larger proportion of fuel for decomposing a certain quantity of coal than the cylindrical retorts.

[11] At the Birmingham Gas Works.

Semi-cylindrical retorts, with the base of the retort bent inwards, so as to give the vessel a kidney-shaped form, have likewise been tried. But this shape is still less advantageous; they could not be made to work uniform, they required more heat, and their deterioration was more rapid than cylindrical retorts. They could not be kept fit for use when worked day and night, more than about five months. And with regard to ellipsoidal retorts, it must be confessed, that the experiments that have as yet been made upon a large scale to ascertain their powers, are not of a nature to enable us to decide on their merits. No experiments have been carried on with retorts of this description in the metropolis for a sufficient length of time, with that care and attention which the subject demands, to ascertain their comparative power. From what however has been done, there is reason to believe that ellipsoidal retorts, might be found more advantageous, than those of a cylindrical form now in use. An ellipsoidal retort, 20 inches by 10 in diameter, and six feet long, weighs 14 Cwt.

The reader will thus observe, that of all the forms of retorts which have been hitherto fairly tried, upon a large scale, it has been satisfactorily ascertained, (excepting only as to the ellipsoidal retorts), that the cylinder is the best form for decomposing coal in masses, from five to eight or ten inches in thickness.

It is perhaps needless to state that in making experiments on the comparative value of the best form of cast-iron retorts, it is obvious that the operations should be continued for some months uninterruptedly; no conclusion can be drawn that may become practically useful in the large way, from processes carried on for a few weeks only. It is absolutely essential that the comparative trials be continued for months together, and that the inferences be taken from the total quantity of coal used during that period, compared with the total quantity of gas obtained, the deterioration of the retorts, and the time and labour expended.

Proceeding on erroneous data, many have persuaded themselves of having noticed that parallelopipedal and semi-cylindrical retorts last longer fit for use than those of a cylindrical shape, an assertion of which subsequent trials, conducted in the manner just stated, has clearly shown the fallacy. Enough has been done at the different gas works in the capital to settle this point, and there is now but one opinion amongst those who are best qualified to judge of the subject. Every body who has made the trial on a large scale, is convinced as already stated, that the best form of the retort for manufacturing coal gas where the process is conducted on the plan of decomposing coal in masses or layers of from four to eight inches in thickness, is a cylinder six and a half feet long, and one foot in diameter, and accordingly retorts of this shape and dimensions are now used in all the best regulated gas establishments in the metropolis.

A cylindrical retort of the description before named, weighs about nine and a half to ten hundred weight. These and all other shaped retorts are furnished with a moveable lid or cover having a conical edge to fit the mouth-piece; the cover is rendered air-tight, not as formerly by grinding, a mode which was costly, but by the interposition of a thin coat of loom, between the lid and the mouth of the retort.

The mouth-piece forms a separate part of the retort. It is bolted and screwed to a flanch which terminates the mouth of the retort, so that when the retort is worn out, the mouth-piece may be detached and applied to new retorts.

There are now in action 620 cylindrical retorts, at the two chartered Gas Works[12] in the metropolis; and the total number of retorts at all the London gas establishments amounts to 960.

[12]

Application of heat.—Flue Plan originally adopted.

It must be obvious that the durability of the distillatory apparatus, greatly depends on the manner in which the heat is applied, to effect the decomposition of the coal contained within the retort. If the heat be very intense the whole vessel is rapidly destroyed. If it be too languid, the distillatory process is protracted, and much fuel, time, and labour wasted to no purpose; and the retort is speedily deteriorated, if the heat acts upon one part of it more than upon another.

The different kind of retorts of which a description has been given in the preceding pages, were originally heated by means of flues passing under and over them. The retorts were placed horizontally and fixed in brick-work. One fire-place at the extremity of the mouth of the retort where the coals are introduced, and whence the coke is withdrawn, was allotted to every two retorts in the series.

At the commencement of the new art of procuring light the quantity of fuel as before stated, necessary to decompose a given quantity of coal, amounted to from thirty to thirty-six per cent of the coal decomposed; that is to say, it required from thirty to thirty-six parts of fuel to decompose one hundred parts of coal. This quantity has been much lessened by a better mode of setting the retorts, and it is now the general opinion that the operation of decomposing coal, by means of cylindrical, parallelopipedal, or semi-cylindrical retorts, must be considered as well conducted when one hundred parts of coal are decomposed by twenty or twenty-five parts of fuel. This appears to be the minimum quantity of fuel, that can be employed for the complete decomposition of coal by means of these retorts, and with the least deterioration of the distillatory vessel.

The following statement will exhibit what has been done in this branch of art.

Report on a course of Operations, made with sets of 66, of 30, of 116, and of 64 retorts, worked on the Flue Plan.

In order to determine the relative value of the best method of setting cast-iron retorts, it was deemed necessary to ascertain whether three retorts might not be heated, instead of two, as before stated, by one fire-place and branching flues. To determine this the following processes were carried into effect.

Process I.

Sixty-six cast-iron cylindrical retorts, of the usual size, namely, six and a half feet long, (exclusive of the mouth-piece) and one foot in diameter, internal dimensions, where set on the plan of three retorts to one fire-place, at the Westminster gas-work station, and a series of 30 similar retorts were erected at another station belonging to the same company, at the East end of London.

The experiments were pursued with every degree of justice in the detail, the retorts were kept in action day and night for upwards of four months, and the results noted down with exactness. The final reports from the two establishments were found to concur in showing that nothing was to be gained by this method over that previously in use.

The time occupied for the distillatory process was not abridged. The consumption of fuel was greater—no larger quantity of gas was obtained from the quantity of coal carbonized. The produce with regard to coke was in the usual ratio, and the retorts were destroyed in about one third less time than when only two were heated by one fire-place.

Process II.

The apparently conclusive results of these experiments did not, however, prevent another set of experiments from being made on the same principle, extended even a degree farther. The problem now proposed to be solved, was, whether four retorts might not be heated with economy, in a manner which had been found already wasteful with respect to three, that is, whether four instead of two retorts might not be heated economically by means of one fire-place.

On this plan one hundred and sixteen cylindrical retorts of the usual dimensions were again erected at the Westminster gas establishment, and sixty-four at another station belonging to the same chartered company. These retorts were kept in action in the best possible manner night and day, and the results, as might have been anticipated, only served to confirm the facts already established by experiment with three retorts.

Nothing was found to be gained; and so far from their being any saving in respect of fuel and wear and tear of the retorts, the waste beyond that which takes place on the plan of two retorts to one fire-place, was increased to nearly twenty-five per cent., accompanied by a corresponding acceleration of injury to the retorts.

It was still imagined, however, that the great waste of fuel and the ultimate unfavourable result of these proceedings, which were repeated with as little success at several other gas-works in the metropolis with parallelopipedal retorts, and at other works with retorts of a semi-cylindrical form, set in a way different from that pursued at the Westminster station, might probably have been owing to the unavoidable circumstance, that the heat was not made to act upon all the retorts employed uniformly in each series of four retorts, but in a manner so variable that one, or even two of the series would become destroyed and rendered useless, while the others continued uninjured in a sound and working state.

The excessive waste of fuel was occasioned, we are told, by the number of injured retorts, which became useless, and were nevertheless required to be kept red hot to no purpose; for it was actually found that when one retort of a series of four became injured, the same fire which had heated the whole four, still required to be kept up to maintain in action the remaining three of the series, and so on with respect to the whole range, till ultimately when there might remain only eighty retorts actually in use, as many fire-places were required to be in full action as would have been sufficient to serve for one hundred retorts.

Attempts accordingly were now made to get over this supposed cause of the losing results, already obtained from the plan of four retorts to one fire-place, by a new series of similar operations, in which the retorts were fixed in such a manner, that those which happened to become injured during the process, might easily and immediately be withdrawn without materially disturbing the rest, and replaced by new ones. The waste of fuel was, it is clear, greatly lessened by the expedient; yet still upon the whole there was no such variation from the general results obtained by the preceding experiments, as to justify the adoption of this plan of increasing the number of retorts worked by one fire-place, on any principle of sound economy.

The great obstacle, as the reader will at once perceive, to working more than two retorts, no matter whether cylindrical, or of any of the other forms before named, with economy, by means of one fire-place, evidently arose from the difficulty of conducting the heat by means of flues around the series of retorts, in such a manner that the heat shall act with equal force on all the retorts.

It is almost needless to state, that the construction of the fire-places, and the direction of the flues for applying the heat to the retorts, were varied by different workmen, who prided themselves on being able to aid the object in view, but the result always showed even that when the draft of the fire-place was well obtained, the action of the heat upon the series of retorts could not be distributed equally and kept up uniformly, except at a great expence of fuel and vast deterioration of the distillatory vessels. The retorts always became injured more in some parts than in others. The concentration and rapidity of the draught of the fire, beyond a certain velocity was always found highly injurious to the retort, and this observation has been since amply confirmed.

In a well constructed furnace, the deterioration of all the retorts in the series is uniform over the whole vessel; no part of the retort is burnt out, as the workmen call it, sooner than another part; and whenever the contrary happens, we may pronounce the fire to be badly applied. When there is such misapplication of the heat, the manufacturer cannot depend upon the duration of the distillatory vessel; he is always in a state of uncertainty with regard to their wear and tear, and it not unfrequently has happened, under such circumstances, that a whole series of retorts have become suddenly deteriorated.

Oven plan lately adopted.

The results before detailed, with regard to the mode of setting cylindrical retorts suggested the propriety of an entire change in the mode of applying the heat, and this was at length fully carried into effect by the adoption of ovens, or air furnaces, in which the retorts are equally exposed to the action of heat on all sides. Mr. Rackhouse has the merit of having first carried into effect this method, since generally known by the name of the oven plan.

The first experiments with these ovens were made on only one retort, exposed in an oven to air intensely heated; but they were afterwards repeated on two, three, four, and five retorts, successively. The retorts suffered the action of heat thus applied, exceedingly well; their deterioration was uniform, and the quantity of fuel required to work them, was found always to be in a direct ratio to the number of retorts employed. These experiments were carried on for upwards of nine months, and it was found, that with five retorts in one oven, so that the heated air could act upon all of them equally, without the flame being directed forcibly upon them, this plan had a decided advantage, in point of economy, over every other method previously adopted. Each oven, containing five retorts, is heated by means of three fire-places, and although it is true that the number of retorts is less by one, than what could have been heated by three fire-places, on the original plan of two retorts to one fire, yet still this method has been found to be far more productive. The front wall of the oven may be readily taken down so that a retort, when damaged, may be withdrawn, and replaced without materially disturbing the rest.

The oven plan of applying heat has been found equally advantageous for parallelopipedal and semi-cylindrical retorts.[13]

[13] The only gas-light establishment of great extent in the metropolis, at which parallelopipedal retorts are still in use, is the South London Gas Works. But it is solely owing to the very peculiar care and economy with which all the details of this establishment are conducted, under the immediate superintendence of a few active, skilful and scientific proprietors, that they are able to compensate for the loss, which in all ordinary cases is inseparable from the employment of vessels of that description.

Description of the Retort Oven.

Fig. 1, [plate IV.], represents a transverse section of one of the retort ovens now in action at the Westminster Chartered Gas-Light Company’s Works; similar ovens are likewise in use at the City of London Chartered Gas-Light Works, and in many other provincial gas establishments.

Fig. 2, [plate IV.], exhibits a longitudinal section, and fig. 1, [plate V.] shows the front elevation of the oven, built about ten feet above the ground, upon piers or arches, which saves brick-work and allows a stage or platform to be erected in front of the fire-places of the ovens. See fig. 2, [plate IV.]

Between the back part of the ovens and the wall of the building in which they are erected, is left an empty space of a few inches to prevent the heat of the oven being communicated to the wall, as is seen at Y in fig. 2, [plate IV.]

The whole interior of the oven, as well as the horizontal flue which pass underneath the crown of it, near the upper tier of retorts, is lined with fire bricks. The uppermost part or crown of the arch is constructed of large fire bricks of such a shape as will allow to flatten the upper part of the arch as much as possible, in order to contract the space between the two upper retorts and the crown of the arch of the oven.

R. R. fig. 1, and 2, [plate IV.] and fig. 1, [plate V.] are cylindrical retorts, placed horizontally in the oven, the lower series are either supported by a large fire-brick, placed edgeways underneath the retort, or by means of a stout wrought-iron pillar, as shown in the design. The two upper retorts are supported by wrought iron straps, T, T, T, fig. 1, and T, fig. 2, [plate IV.] The straps pass through the brick-work of the upper part of the oven, as shown in the designs, and they are secured with screws and nuts to an iron bearing bar, the extremities of which are supported by the outer walls of the oven. Each retort is furnished at the extremity opposite to the mouth-piece, with a short projecting piece or tail let into the brick-work of the oven, as seen in the design, fig. 2, [plate IV.]

M. Fig. 2, [plate IV.] shows the mouth-piece of the retort with its cross bar and hand-screw; and fig. 6, [plate V.] shows the mouth-piece drawn to a larger scale. E. is the hand-screw, with its cross or bearing bar D, which passes through the projecting arms C. C. The lid of the mouth-piece has a conical edge, so that it fits close when pushed into its place by means of the hand-screw E. Fig. 7, [plate V.] is the lid which closes the mouth-piece; the handscrew E, fig. 6, presses the lid close, to render it air-tight, a thin stratum of loom luting being first applied to the orifice of the mouth-piece.

F. fig. 2, [plate IV.], is the fire-place, with the ash-pit E of the oven. The door of the ash-pit is provided with three slits covered within by a register slide, to regulate the admission of air as occasion may require.

The fire passes freely and uniformly round all the retorts, and the whole cavity of the oven acquires an equable temperature, which it retains, if the workman takes care to admit as little air as possible, through the register door of the ash pit, when the upper part of the arch, or crown of the oven has acquired a bright cherry red heat.

We have stated already that in front of the oven, is a platform, as represented in the sketch, fig. 2, [plate IV.] In the floor of this platform, and directly underneath the mouth-piece of the retorts, all of which project beyond the brick-work of the oven, is an opening covered with an iron trap door; through this door the red hot coke, discharged from the retorts, is suffered to fall below the stage or platform into a cellar, or other fire-proof place, that it may not annoy the workmen. O, O, fig. 1, [plate V.] denotes this opening through which the coke falls.

P, fig. 2, [plate IV.], and P. P. fig. 1, [plate V.] is a pipe proceeding perpendicularly from the upper part of the mouth-piece of each retort, the other extremity of which descends into the horizontal hydraulic main H, which is shown in fig. 2, [plate IV.] and [plate V.], supported upon iron columns. This pipe serves to convey away the liquid and gaseous products which become disengaged from the coal in the retort during the distillatory process.

The liquid substances, namely the tar and ammoniacal fluid, collect in the hydraulic main H, [plate IV.] and [V.], which is furnished with a perpendicular diaphragm or partition plate to cause a certain quantity of the liquid deposited in it to accumulate to a certain height, and thus to seal the perpendicular pipe P. The liquid cannot flow out of the horizontal pipe H, till it rises to the level of the diaphragm. This arrangement is distinctly shewn at H. fig. 2, [plate IV.], where the diaphragm or partition plate is seen in the section of the hydraulic main, together with the extremity of the perpendicular pipe P., descending into the fluid contained in the hydraulic main.

K, Fig. 1, [plate V.] is the discharging pipe, connected with the upper part of the horizontal main H: it serves to convey away the gaseous and liquid products from the hydraulic main H. By means of this pipe the tar and ammoniacal fluids are conveyed into any convenient reservoir, called the tar cistern, which is perfectly air-tight, and from this vessel the liquid may be drawn of by means of a pipe or stop-cock. The extremity of the pipe which communicates with the liquid, is bent downwards, so that no air can enter the vessel: this arrangement is shown at fig. 3, [plate II.]

It is essential that the condensation of the vaporous fluids should be fully completed before they reach the tar cistern. To effect this, there is usually allowed a considerable distance to intervene between the discharging pipe K, fig. 1, [plate V.], and the reservoir destined to receive the condensible products; or the pipe is made to pass through a vessel containing water, called the condenser, which acts in a similar manner as the refrigeratory of a common still. It is obvious that it is immaterial how the condensation of the vaporous fluid is effected; it is essential, however, that the condensation should be complete before the liquid tar and ammoniacal fluid reach the reservoir destined to receive these products.

The gaseous fluid which accompanies the condensible products, are then made to pass into the lime machine, of which we shall speak hereafter, in order to be deprived by means of quick-lime and water, from the portion of sulphuretted hydrogen and carbonic acid gas which was combined with the gas. And when this has been accomplished, the purified gas is conveyed into the gas-holder, where it is stored up for use. This part of the operation will be rendered more obvious hereafter. In some establishments, the hydraulic main is furnished with two discharging pipes, the one carries away the condensible fluid, into which the perpendicular pipes P, fig. 2, [plate IV.] dip, whilst the other serves to convey away the gaseous fluids to a condensor, in order to deposit the vaporous portion of condensible liquid it may contain, and from thence the gas passes into the purifying apparatus, or lime machine. X, fig. 2, [plate IV.], is a small screw plug, which, when opened, restores the equilibrium of the air within and without the retort previous to the lid being taken off, to prevent the loud report, which otherwise happens when the lid or cover of the retort is suddenly removed. To avoid these explosive reports which had become a nuisance to the neighbourhood of gas works, the practice of gradually withdrawing the lid of the retort, and at the same time presenting a lighted torch has been adopted at some works, which fully remedies the evil.

The number of retort ovens at the Westminster Chartered Gas Works’ Stations, amounts to four hundred and ninety.

PART V.

Difference in the quantity of Gas evolved during different periods of the distillatory process, and economical considerations resulting therefrom in the manufacture of Coal Gas.

In conducting the decomposition of coal, the evolution of the gas is far from being, with regard to quantity, uniform during different periods of the distillatory process. The formation of the gas is more rapid in the beginning of the process, and gradually slackens as the operation proceeds. The gas also differs in its chemical constitution, at different periods of the process; although in the case of large supplies, this difference is of little consequence after the gas is purified in the usual manner. The former consideration, however, has given rise to various modes of operating, of which it will be proper to take some notice.

It must be obvious, that in proportion as the mass of coal in the retort becomes carbonized or converted into coke, the exterior surface becomes a gradually increasing obstacle to the action of the heat upon the interior or central part of the coal remaining to be decomposed. The heat required on that account must be more intense, and kept up to no purpose, and the extrication of gas becomes slower and slower, as the operation proceeds.

The loss occasioned by this rapid diminution of the means employed, is serious in every point of view, in regard as well to the quantity of fuel used and time wasted, but it is unavoidable in the operation of decomposing coal in masses or layers from 5 to 10 inches in thickness, and must be a great drawback on the value of the gas-light discovery.

The loss of fuel, it is obvious, must be just in proportion to the quantity of carbonised matter, or coke, which is kept hot to no purpose, awaiting the decomposition of that portion of coal, which it is the very means of protecting from becoming decomposed.

A striking exemplification of this statement will be seen in the following table, exhibiting the result of the progressive produce of coal gas, obtainable, in a given time, by means of cylindrical and parallelopipedal retorts.

Experiment with one cylindrical Retort, containing two bushels of coal.

The quantity of gas is at the rate of ten thousand cubic feet to the chaldron (27 cwt.) of coal.

Experiment[14] with eighteen cylindrical Retorts, containing one chaldron of coal.

This experiment was made with retorts set on the flue plan.

The coal employed was (Bewick and Craister’s Wall’s End), Newcastle coal.

[14] Communicated by Mr. T. S. Peckston, of the Westminster Gas Works.

Experiment with thirty-six parallelopipedal retorts, each containing two bushels of coal.[15]

[15] Own Experiments.

The same heat as we have seen from the preceding table, [p. 79], which is necessary during the first hour of the operation, for the evolution of one hundred and fifteen cubic feet of gas, is required in the eighth hour for the production of no more than forty-two cubic feet, being a decrease in effect of nearly two-thirds.

When larger retorts are employed for decomposing coal in masses, from five to ten inches in thickness, the loss of heat is in a much greater ratio.

In the hope of remedying in some measure the evils thus distinctly ascertained to arise from the undue thickness of the masses of coal subjected to the distillatory process, there have not been wanting manufacturers who have had recourse to experiments on a large scale, to ascertain with certainty whether they might not be gainers by suffering the distillatory process, when the retorts are charged with two bushels of coal, to proceed only for the space of six hours, instead of eight. But the result of these experiments, as will be presently explained, has shown satisfactorily that it is more profitable to keep up the distillatory process for a period of eight hours, with the retorts fully charged, than to abridge the operation by terminating it at the end of six hours.

Others again, have imagined, that it would be more economical to decompose a less quantity of coal at once, or to decrease the thickness of the stratum of coal in the cylindrical, or in any of the before named retorts; but then again, serious difficulties occur in the practice. The more frequent charging of the retorts and luting on the covers,[16] which such a mode of operating require, occasions a prodigious waste of fuel, time and labour. A greater number of retorts and more workmen must likewise be employed, in order to produce the requisite quantity of gas daily, which the manufacturer is called upon to supply; more space of ground is required, and more dead capital must be sunk in the establishment. The more frequent and sudden alterations of temperature which the retorts necessarily suffer, by the more frequent introduction of cold coal, renders them extremely liable to become injured; and it is almost impossible to maintain a number of retorts thus worked, at an uniform temperature.

[16] When the cover is ground on, air-tight, the cost of the retort is much increased.

From various statements, which I have been favoured with, in confirmation of my own observations on the best method of working cylindrical retorts, it may suffice to lay before the reader the result of a series of operations instituted by one of the largest and best conducted establishments in this country; the public-spirited and indefatigable directors of which have done more in the way of extensive, costly, varied and long continued experiments, to improve the new art of lighting with gas, than any other similar body in the kingdom; and without whose exertions the gas light illumination would never have reached the state of perfection it has attained.

Report on a course of Experiments made to ascertain the comparative Economy[17] of manufacturing every week, 857,667 cubic feet of gas, by means of Cylindrical Retorts variously worked.

[17] The cost of materials and price of labour in this estimate, as well as in all subsequent statements, is given such as they actually were, at the time, when the experiments to which they refer were made.

Gas Light and Coke Company’s Works,
Westminster Station.

February 8th, 1819.

Sir,

Enclosed are the result of a series of experiments made under my direction with a view of ascertaining the relative value of the different modes of working cast-iron cylindrical retorts, from which you will perceive that it is more economical to work eight hours charges, as the workmen call it, that is to say, to suffer the distillatory process to go on for eight hours, when nearly two bushels of coal are contained in each retort, than to discontinue the operation at the end of six hours.

I am with respect,
Sir, Yours, &c.
T. S. Peckston.

To Mr. F. Accum,
Compton Street, Soho.

Process A.

[18] Average proportion of gas from a chaldron of coal.

Expenditure of Process A.

Products of Process A.

Hence the amount of expenditure for procuring 857,667 cubic feet of gas, is £ 360. 17s.

The value of the saleable products £ 846. 10s. 6d.

And the average proportion of gas obtained from one chaldron of Newcastle coal, 8,300 cubic feet.

Process B.

[19] Average proportion of gas from a chaldron of coal.

Expenditure of Process B.

Products of Process B.