Chapter VI: Part II: Gas-Light (2)

The nature of carburetted hidrogen obtained from coal varies considerably according to the conditions under which it is obtained. The first part is always much heavier than the last, though still lighter than common air, and holds in solution a portion of oil, for on standing for some time over water it becomes lighter, and is found to require less oxygen for saturation than before. The oil which it held suspended, then becomes precipitated. The average specific gravity of the first and last gas mixed, which may be taken as an average of the whole specific gravity is to that of common air as 2 to 3--112lb. of common cannel coal produce at its _minimum_, from 350 to 360 cubic feet of carburetted hidrogen gas; but the same quantity of the best Newcastle coal, that is to say, such as coke, which, when laid on the fire readily undergoes a kind of semi-fusion, and sends out brilliant streams of flame, produces upon an average from 300 to 360 cubic feet of this gazeous fluid, besides a large portion of sulphuretted hidrogen, carbonic oxid and carbonic acid. Half a cubic foot of this carburetted hidrogen, fresh prepared, that is to say, holding in solution or suspension, a portion of the essential oil, which is generated during the evolution of the gas, is equal in illuminating power to from 170 to 180 grains of tallow, (being the quantity consumed by a candle six to the pound in one hour.) Now, one pound avoirdupoise is equal to 7000 grains, and consequently one pound of candles of six in the pound, burning one at a time in succession, would last (if we take 175 grains of tallow to be consumed in an hour) 7000/175 = 40 hours. To produce the same light we must burn one half of a cubic foot of coal-gas per hour; therefore, one-half multiplied by forty hours is equal to twenty cubic feet of gas in 40 hours, consequently equal to one pound of candles, six to the pound, provided they were burnt one after another. One hundred and twelve pounds of cannel-coal, produce, at its _minimum_, three hundred and fifty cubic feet of gas; and are equal to three hundred and fifty, divided by twenty, which last is equivalent to one pound of tallow, making one hundred and twelve pounds of cannel-coal, equal to 350/20 = 17½lbs. of tallow. Further, one hundred and twelve pounds of cannel-coal, divided by seventeen and a half of tallow make six and four-tenths of cannel-coal, equal to one pound of tallow.

With regard to Newcastle coals[17], it may be stated that one chaldron of Wall’s-End coal may be made to produce in the large way upwards of 11,000 cubic feet of crude gas; which, when properly purified, diminishes to nearly 10,000 cubic feet.

[17] One chaldron of Newcastle coal weighs from 2850 to upwards of
2978lb.

The production of carburetted hydrogen, both with regard to quantity and quality from the same kind of coal depends much upon the degree of temperature employed in the distillatory process. If the tar and oil produced during the evolution of the gas in its nascent state, be made to come in contact with the sides of the red hot retorts, or if it be made to pass through an iron cylinder or other vessel heated red hot, a large portion becomes decomposed into carburetted hydrogen gas and olifiant gas, and thus a much larger quantity of gas is produced than would be obtained without such precaution from the same quantity of coal.[18]

[18] One pound of coal-tar produces 15 cubic feet of carburetted
hidrogen abounding in olifiant gas.

The distillation of the coal, (if gas be the chief object) should therefore not be carried on too rapidly. Most of the retorts used in the large way, are calculated for containing about one hundred weight of coal, and in general, when previously heated, produce from two and one-half to three cubic feet of gas, in four hours for each pound of coal they contain; but when the layer of coals in them does not exceed four inches in depth, three and one-half to four feet of gas may be obtained in the same time.

The retorts best calculated for large gas-light works are seven or eight foot long (without the mouth-piece) and twelve inches in diameter, tapering down to ten inches--if they are larger the coal which they contain cannot be heated properly. The advantages that may be derived from the circumstances before stated are of greater value in the gas-light manufacture than is often imagined, and the quantity as well as the quality of the gas is very much influenced by such circumstances. If coal be distilled with a very low red heat scarcely observable by daylight, the gas produced gives a feeble light--if the temperature be increased so that the distillatory vessel is of a dull redness, the light is more brilliant and of a better colour--if a bright or cherry-red heat be employed the gas produced, burns with a brilliant white flame, and if the heat be increased so far that the retort is almost white hot, and consequently in danger of melting, the gas given out, has little illuminating power, and burns with a clear blueish flame;[19] or if the coal abounds in pyrites or sulphuret of iron, as is sometimes the case with Newcastle coal, a large quantity of sulphuretted hidrogen is likewise evolved, which although it increases the illuminating power of the coal-gas, has the capital disadvantage, of producing an intolerable suffocating odour, when the gas is burnt which is particularly perceptible in low rooms illuminated with such gas.

[19] It is chiefly a mixture of carbonic oxid, and hydrogen gas.

These observations also apply to the distillation of tar, which when distilled either in a vaporous or nascent state, during its first production from coal in the ordinary process, or if it be submitted to a second distillation, mingled with a fresh portion of pit-coal, a practice usually had recourse to when this product cannot be disposed of more advantageously. The best depth of coal in the retort for procuring excellent gas, and at the same time for yielding the greatest quantity from the same weight in the shortest possible time, is about six inches.

The brightness of the coal-gas flame is rather diminished when the gas has been long kept over water, and hence for illumination it should be used as soon as prepared, but of course properly purified.

The quantity of gas taken up by water is affected by temperature, because the temperature increases its elasticity; the quantity of gas absorbed, diminishes as the temperature increases, and increases as the temperature diminishes. ½7 part of its own bulk of pure coal-gas is absorbed by the water over which it is confined in the gazometer.

The chemical constitution of this gazeous fluid is best ascertained by burning it in a vessel of oxygen gas, over lime-water in a pneumatic reservoir, by means of a bladder and bent brass pipe. Two products are then obtained, viz. water and carbonic acid. That water is produced, may be shown by burning a very small stream of the gas in a long funnel-shaped tube open at both ends. The formation of carbonic acid is evinced, by the copious precipitation of the lime-water in the foregoing experiment.

If carburetted hydrogen be mixed with a sufficient quantity of oxygen gas or common air and fired by the electric spark, or by any other method, an explosion takes place more or less violent according to the quantity of carbonaceous matter condensed in the hydrocarbonat; and the remaining gas consists of carbonic acid, together with any unconsumed gas, or excess of oxygen, whilst the water condenses in drops on the sides of the vessel. A few cubic inches of the mixed airs is as much as can be conveniently managed at a single explosion; and when any portion of olefiant gas is present, even this quantity will endanger very thick glass jars. A very vivid red flame appears at the moment of the explosion, and a great enlargement takes place in an instant, after which the bulk is suddenly reduced to much less than the original quantity. When the carbonic acid is absorbed by lime-water, if the gasses have been properly proportioned, no gazeous residue is left, except accidental impurities. Though carburetted hydrogen gas, is sometimes naturally produced in coal-mines, and occasionally mixes with common air, producing dreadful explosions, yet when coal-gas is mixed with common air, it does not explode unless the gas be to the air as 1 to 10 nearly. Such are the leading chemical habitudes of this gazeous product. The varieties of carburetted hydrogen gas all agree in being inflammable; but they possess this property in various degrees, as is evinced by the variable brightness of the flame which they yield when set on fire.

“Messrs. SOBOLEWSKY and HORRER, of St. Petersburgh, have employed wood for the purpose of producing carburetted hydrogen gas. The pyroligneous acid obtained in this operation, when freed from the empyreumatic oil with which it is mixed, becomes acetous acid, and is applicable to all the uses of vinegar. A cubic cord of wood equal to 2.133 French metres (a metre being rather more than an English yard), yields 255 Paris pounds of charcoal, and 70 buckets of acid. The latter gives 30 pounds of tar, after the extraction of it 50 buckets of good vinegar remain. The same quantity of wood furnishes 50,000 cubic feet of gas, sufficient for the supply of 4000 lamps for five hours.”[20]

[20] See Repository of Arts, Vol. XI. No. 36, p. 341.

UTILITY OF THE GAS-LIGHT ILLUMINATION, WITH REGARD TO PUBLIC AND PRIVATE ECONOMY.

From what has been stated in the preceding pages it becomes obvious, that a substance yielding an artificial light may be obtained from common coal in immense quantities. The attempt to derive advantage from so valuable a discovery is surely no idle speculation. Let us therefore now consider to what objects of public and private utility this mode of procuring light may be applied with effect. It is obvious that coal-gas may be preserved in a reservoir for any length of time and that it may be conveyed by means of tubes to any distance flowing equably and regularly like water. Those, indeed, who have not seen the contrivance will find it difficult to imagine with what ease it is managed. The gas may be distributed through an infinity of ramifications of tubes with the utmost facility. Near the termination of each of the tubes through which it flows, it is confined by a valve or stop-cock, upon turning which, when required to be lighted, it flows out in an equable stream and ascends by its specific levity. There is nothing to indicate its presence; no noise at the opening of the stop-cock or valve--no disturbance in the transparency of the atmosphere--it instantly bursts on the approach of a lighted taper, into a brilliant, noiseless, steady and beautiful flame. Its purity is attested by its not blacking or soiling in the least degree the metallic orifice from which it issues, nor even a sheet of white paper, or polished surface brought in contact with it. There is no escape of combustible matter unconsumed, which is so great a nuisance in all our common lights. The products of the combustion are water and carbonic acid gas[21]. The accurate and elegant experiments of Dr. W. HENRY have shewn in the most satisfactory manner, that considerably less carbonic acid is produced by the flame of coal-gas, than by that of oil, tallow, or wax[22], which sufficiently refutes the absurd notions that have been circulated respecting the pernicious effects of gas-lights. But if the gas from Newcastle coal is badly prepared, or not deprived of the portion of sulphuretted hydrogen, which it usually contains, it then emits fiery sparks and produces a portion of sulphureous acid by virtue of the union of the oxygen of the air with the sulphur dissolved in the gas, the consequence of which is, a suffocating odour, which is particularly observable in the higher stratum of the air of apartments in which the gas is burnt. Such gas likewise tarnishes all metallic bodies--it discolours the paintings effected with metallic oxids, and always produces a suffocating odour very noxious to health. It is freed from the sulphuretted hydrogen and may be rendered fit for illumination by passing it repeatedly through very dilute solutions of sub-acetate of lead, green sulphate of iron, quicklime and water, or hyper-oxymuriate of lime.

[21] The water (which passes off in imperceptible vapour) is generated
by part of the oxygen of the air uniting with part of the hydrogen,
which forms the great bulk of the coal-gas: and the carbonic acid gas
is produced by the union of another portion of the oxygen uniting with
the smaller portion of carbon, which is the other component part of
the coal-gas.

[22] 100 Cubic inches of carburetted hydrogen from coal, require for
burning 220 cubic inches of oxygen and produce 100 cubic inches of
carbonic acid--100 cubic inches of the same gas obtained from wax,
require for burning 280 cubic inches of oxygen and produce 137 cubic
inches of carbonic acid--100 cubic inches of the same gas procured
from lamp-oil, require 190 cubic inches of oxygen for burning, and
produce 124 cubic inches of carbonic acid.

The following lines relating to the salubrity of the gas-light
illumination are copied from Mr. Lee’s evidence in the House of
Commons, when examined on that subject.

Question--“Is the health of your manufacturers at all affected by the
use of gas?--Answer--Not in the least, or I would not have adopted it.
I believe I explained to the Committee, that I used the gas-lights in
my own house first.”

Q. “You have not seen the smallest alteration in the health of your
workmen?--A. Not in the least, for had I seen it, it would have been a
fatal objection to it.”

Q. “And you say the same in regard to the use of the gas-lights in
your own family?--A. Certainly I do.”

As to the brilliancy of the flame, an appeal may be made to every one who has witnessed the gas-light illumination, whether it be not superior to the best wax candle-light, or the light of Argand’s lamps.

It may be described as a rich compact flame, burning with a white and agreeable light. It is also perfectly steady, when the flame is limited to a moderate size: in large masses, it is subject to that undulation which is common to it with all flames of certain dimensions, and is caused by the agitation of the surrounding atmosphere. The gas flame is entirely free from smell. The coal-gas itself certainly has a disagreeable foetid odour before it is burnt, so has the vapour of wax, oil, and tallow, as it comes from a lamp or candle newly blown out. This concession proves nothing against the flame of gas which is perfectly inodorous, a white handkerchief, passed repeatedly through it and applied to the nose, excites no odour.

Another peculiar advantage of the gas flame is, that it may be applied in any direction we please, as there is nothing to spill and the gas is propelled by a certain force which is always the same, it will burn equally well in an almost horizontal as in an upright position; and we can thus obviate two great objections to all our artificial lights, that their least luminous end is directed downwards where the light is generally most wanted, and that a shade is cast below by the stand or support of the combustible matter.

The size, shape and intensity of the gas-flame may be regulated by simply turning a stop-cock which supplies the gas to the burner. It 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 such lights may be in nurseries, stables, warehouses, in the chambers of the sick, &c.

From the facility with which the gas-flame can be conveyed in any direction, from the diversified application, size and shape which the flame can be made to assume, there is no other kind of light so well calculated for being made the subject of splendid illuminations.

Where lustres are required in the middle of a room, the best mode of conducting the gas to the chandelier, is to pass the gas-pipe through the ceiling from the room above, immediately over the lustre. This can be easily done without injury to the apartment.

Where side-lights and chandeliers are required the tubes need never appear in sight, but may be concealed in the wall or floor of the house. When transparencies are wanted as decorations for halls, lobbies, &c. more than light, recesses may be filled with different coloured _media_, or paintings, and any intensity of light may be thrown on the object.

If a number of minute holes are made in the end of a gas pipe, it forms as many _jets de feu_, which have a very brilliant appearance; these may sometimes be placed in the focus of a parabolic reflector. In cases where the light is required to be thrown to a distance, other burners are constructed upon the same principle as the Argand lamp, forming a cylinder of flame, and admitting a current of air both to the inside and outside.

On comparing the flame of a gas-light with the flame of a candle whatever its size may be, it appears just as yellow and dull as the flame of a common lamp appears when compared with that of a lamp of Argand. The beautiful whiteness of gas-light never fails to excite the surprize and admiration of those who behold it for the first time.

A large edifice or manufactory lighted by gas, contrasted with one of the same kind lighted by candles or lamps, resembles a street on the night of a general illumination, compared with the glimmering light of its ordinary parish lamps.

The intensity of one of the parish gas-light lamps, now exhibited in the streets of this metropolis, will bear ample testimony of this assertion; the light of the parish gas-lamps, is to the intensity of the parish oil lamps as 1 to 12.

One of the most obvious applications of the gas-light illumination unquestionably consists in lighting streets, shops and houses; and let it be observed that as this is found safe and economical, it proves all that the most ardent friends of the gas-light system can desire. For in contending with the common mode of lighting the streets and shops, the new lights must beat out of the market the cheapest of all artificial lights; and as it has succeeded in doing this it shews in the most satisfactory point of view, the prodigious advantages of gas-lights when compared with the materials of tallow and oil.

The original expence of laying the pipes for conveying the gas, together with the cost of the machinery, is all that is required; the preparation of the gas being itself a lucrative process, no doubt will pay all its expences besides the interest of capital, and leave a surplus of profit.

Indeed the application of the coal-gas, as a substitute for tallow and oil, to illuminate houses, shops, &c. is no longer problematical, a considerable extent of this capital, together with numerous shops and houses being already supplied with this species of light.[23]

[23] The Liberty of Norton Falgate, as far as Bishopgate-street, is
lighted with gas-light, from the Chartered Company’s station at Norton
Falgate; and gas-light pipes are laid from that station as far as the
west end of Cheapside, and in all the streets north of that great
thoroughfare.

In the West end of the Town, the main pipes for supplying the streets
and houses with light from the Gas-Light Company, extend through the
most eligible parts; from their Establishment in Peter-street,
Westminster, along the line from Pall Mall to Temple-bar, compleatly
surrounding the parish of St. Martin’s in the Field. Main pipes are
also placed in the Hay-market, Coventry-street, Long-Acre, St.
Martin’s-lane; and in the principal parts of the parishes of St. James
and St. Ann.

In the East end of the metropolis, the gas-light _mains_ extend from
Cornhill to St. Paul’s, Wood-street, Fore-street, &c.--Consent has
also been given to the incorporated Gas-Light Company for laying their
pipes in the parish of St. Stephen’s in the Field; St. Paul
Covent-garden; St. Mary-le-Strand; St. Clement Danes; St. George’s,
Bloomsbury; St. Giles’s in the Fields; St. Andrew’s, Holborn, above
the bars; part of the parish of St. Mary-la-bonne; besides several
other districts, comprehending the whole of the city and suburbs of
Westminster.

Enough therefore, has been done to prove the possibility of lighting houses, and streets, with gas, which would have been regarded twenty years ago as an extravagant paradox.[24]

[24] I am informed by Mr. CLEGG, the engineer of the Chartered
Gas-Light Company, under whose direction the new system of lighting is
carried on, that the total length of pipe laid down, as mains, in the
streets of London amounts already to nearly 15 miles.

In the Eastern part of London, the same Company is engaged to lay
their pipes in the principal parts of Whitechapel, Spitalfields, St.
Luke’s, and the adjoining neighbourhood.

One part of the city of London, extending from Temple-bar to the West
end of Cheapside; from Newgate-street to Holborn Bars, together with
the intervening streets, is also provided with pipes laid down by
another gas-light association, who have opened a new Establishment in
Water-lane, Fleet-street, but are unconnected with the Chartered
Company. A third company is projected in Southwark, and a fourth in
the Eastern district of London, creating by a rivalry of interest,
that laudable competition which always proves beneficial to the public
at large, and which cannot fail to accelerate the progress of this new
art of procuring light.

The Church of St. John the Evangelist in this metropolis has been illuminated with gas-lights for upwards of two years: the lights employed in this edifice is equal to 360 tallow candles eight to the pound. The avenues to the House of Lords and House of Commons, Westminster-hall, Westminster-bridge; the house and offices of the Speaker of the House of Commons, the Mansion-house, and many other places, deserve to be named, as having already adopted this species of illumination.

Another advantageous application of the gas-light must be the supplying of light-houses.

From the splendour and distinguishing forms which the gas-light flame is capable of assuming, no light is better calculated for signal-lights than this. By means of one single furnace as much gas might readily be procured as would furnish a flame of sufficient intensity, during the longest winter night, exceeding in brilliancy or intensity of light any light-house in Britain or elsewhere.

If every light-house round this island were possessed of a gas-light furnace, one-half part of the enormous expence which they at present require would furnish a much more brilliant light. The cheapness of this light and its efficacy for the purpose, would soon multiply the number of light-houses, and thus most essentially contribute to the security of navigation on our coast. The gas may be made to issue from tubes by long narrow slips, and a surface of flame produced of any given dimensions, and free from all smoke that would obscure the reflectors.

The ease with which the largest gas-light flame is instantly extinguished by shutting the stop-cock, and the readiness with which a long line of gas catches fire by applying a lighted taper to one extremity, are properties that cannot fail to recommend it for the purposes of telegraphic communications by night. Another application of the gas unquestionably might be the lighting of barracks, arsenals, dock-yards, and other establishments where much light is wanted in a small place.

The annual expence of lighting the barracks of Great Britain is said to fall little short of 50,000l. a small part of which on the new plan, would supply them with a much purer and safer light.

The uses of the gas-lights already enumerated must of themselves, justify us in attaching great importance to the discovery, and if reduced to practice all over the kingdom, would employ a large capital in a way the most advantageous and productive. But the utility of this light will be almost indefinitely increased to the use of private families. That such an application is practicable, in all towns of Great Britain, is obvious, from what has been done already, and that it would be highly economical and ornamental, there can be little doubt.

By means of gas we may have a pure and agreeable light at command in every room of our house, just as we have the command of water, with this singular advantage, that these lights may burn for hours within an inch of the most combustible substance without danger, because they neither can burn down like a candle nor emit sparks. These properties make the gas-lights a most desirable light on board our ships of war, where severe regulations are necessary to prevent danger from fire, which after all are frequently evaded. The gas-light might be used in the store-rooms, and even in the powder magazine, and the captain would completely command the supply of light by the possession of the key which opens and shuts the stop-cock. A small apparatus which may be erected at a trifling expence would be sufficient for that purpose.

In shops, counting-houses, and public offices, the advantages are a white light, nearly equal to day-light, a warmth which almost supersedes the use of fires, a total absence of smoke, smell, and vapour, and great economy of labour.

The heat produced by gas-lights must be observed by every one who has had an opportunity of attending to it in the most superficial manner, and the reason why gas-lights produce more heat than oil or candle-light will not appear strange to our chemical readers (and who is there now that does not know something of chemistry?) when it is considered that the gas-light flame condenses more air than the flame of oil and tallow, and consequently must produce more heat.

The flame of gas may be produced in so large a surface, as to be applied to heat the most spacious apartments as well as to light them.

If the gas is made to issue by a circular rim of about twelve inches diameter; it forms a sort of an Argand lamp on a great scale, and it is manifest that a circumference of three feet of flame will heat the air very rapidly, and with such uniformity that we need no longer be exposed to the partial heating occasioned by the strong draft of a large fire. A lamp of this description in the centre of a large room, with a very small fire to secure a gradual renewal of the air would enable us to enjoy the most healthful and agreeable temperature.

From trials made on this subject, I am enabled to state, that three Argand’s lamps, consuming five cubic feet of gas per hour, are sufficient to keep a room 10 feet square at a temperature of 55° Fahr. when the air without doors has a temperature of freezing.[25]

[25] Mr. DALTON’s method of ascertaining the comparative quantity or
effects of heat evolved during the combustion of different inflammable
gases, and other substances capable of burning with flame, as stated
in his System of Chemistry, vol. I. p. 76, deserves to be recommended
to those who are more immediately interested in this subject. The
process, which is simple, easy, and accurate, is as follows:

Take a bladder of any size, (let us suppose for the sake of
illustration, the bladder to hold or to be equal in capacity to 30,000
grains of water,) and having furnished it with a stop-cock and a small
jet pipe, fill it with the combustible gas the heating power of which
is to be tried. Take also a tinned iron vessel with a concave bottom
of the same capacity, pour into it as much water as will make the
vessel and water together equal to the above stated bulk of water in
the bladder, viz. 30,000 grains. This being done, set fire to the gas
at the orifice of the pipe, and bring the point of the flame under the
bottom of the tinned vessel, and suffer it to burn there, by squeezing
the bladder till the whole of the gas is consumed. The increase of
temperature of the water in the tinned vessel being carefully noticed
before and after the experiment, gives very accurately the heating
power of the given bulk of the inflammable gas.

It was thus proved that--

Olefiant gas raises an equal volume of water 14°
Carburetted hidrogen, or coal gas 10
Carbonic oxid 4
Hidrogen 5
Spermaceti oil 10 grains burnt in a lamp raised
30,000 grains of water 5
Tallow 5
Wax 5,75
Oil of turpentine 3
Spirit of wine 2

In all processes of the arts where a moderate heat is wanted the gas-light flame will be found very advantageous--even on a large scale this flame may be used with profit. It possesses advantages which cannot be obtained from flaming fuel, where much nicety is required; because no fuel can be managed like the flame of coal-gas. For it is well known, that when too little air be given to flaming fuel it produces no flame, but sooty vapour; and if too much air be admitted to make those vapours break out into flame, the heat is often too violent. It is a fact, that flame, when produced in great quantity, and made to burn violently, by mixing with a proper portion of fresh air, driving it on the subject, and throwing it into whirls and eddies, thereby mixing the air with every part of the hot vapour, produces a very intense heat.

The great power of a gas-flame does not appear when we try small quantities of it, and allow it to burn quietly, because the air is not intimately brought into contact with it, but acts only on the outside; and the quantity of burning matter in the surface of a small flame is too minute to produce much effect.

But when the flame is produced in large quantity and is freely brought forward into contact and agitated with air, its power to heat bodies is immensely increased. It is therefore peculiarly proper for heating large quantities of matter to a violent degree, especially if the contact of solid fuel with such matter is inconvenient.

As the gas-flame may be made to assume any shape and intensity, and as there is nothing to spill, it may be exhibited under such variety of forms and designs, as cannot fail to give rise to the most tasteful ornamental illumination.

PLATES III. IV. and V. exhibit such designs of different kinds of gas-lamps, chandeliers, lustres, candelabras, &c. as are already in use in this Metropolis.

PLATE III. fig. 1, represents a _Rod Lamp_. The gas passes through the rod _a_, to the Argand burner, which is surrounded by a cylindrical chimney, _c_, swelling out at the lower extremity. The construction of the Argand burner we have mentioned already, _p._ 78.

In all the gas-light burners, constructed on Argand’s plan, care should be taken that the flame be in contact with the air on all sides, and that the current of air be directed towards the upper extremity of the flame. This may be effected by causing a current of air to rise up perpendicular from the bottom of the chimney glass, and to pass out again through the contracted part, or upper extremity of the chimney; but no other current of air should ever be permitted to come near the gas-flame, or enter the glass chimney which covers or defends the light; for if more air be permitted to mix with the flame than is sufficient for the compleat combustion of the coal-gas, it necessarily diminishes the heat, and consequently reduces the quantity of light.

Fig. 2. _A Rod Gas Lamp, with branches._ The gas passes through the hollow rod, _a_, and part of the hollow branch, _b_, to the burner of the lamp. The cylindrical shaped glass, _c_, exhibited in this figure, is not so well adapted for the compleat combustion of coal-gas, as the belly-shaped chimney, _c_, represented in fig. 1, 3, 5, 6, because the ascending current of fresh air is not turned out of its perpendicular course, and thrown immediately in a concentrated state, into the upper part of the flame where the combustion of the gas is less perfect. The exterior current of air which enters at the bottom into the lamp, rises merely with a velocity proportioned to the length of the cylinder, and to the rarefaction of the air in the same, but without being propelled to the apex of the flame, as it should do, and is made to do, in the bellied glass adapted to the lamp, fig. 1.

Fig. 3. _A Bracket Lamp._ _a_, the tube which conveys the gas to the burner; _b_, the stop-cock of the tube.

Fig. 4. _A Pendent Rod Lamp_; in which the gas is supposed to come from a pipe above, through the ceiling, into the pipe, _a_, to supply the burners. The tulip-shaped chimney, _b_, of this lamp, is likewise ill adapted for gas-light burners.

Fig. 5. _A pendent double-bracket Lamp._ The gas passing through the perpendicular tube, _a_, into the brackets, _b_ _b_; _c_ shows the Argand burner.

Fig. 6. _A swing Bracket Lamp._ _a_, the gas-pipe with its stop-cock; _b_, a brass ball, communicating with the pipe, _a_; _c_, the conducting tube, ground air-tight into the ball, _b_, and communicating with the burner of the lamp, so as to allow it to have an horizontal motion.

Fig. 7. Shews the construction of the ball _b_, and pipe, _c_, of the lamp, fig. 6.

Fig. 8. _A Swing Cockspur Lamp_, constructed upon the same plan as fig. 6. These two lamps are very convenient for desks in counting-houses, &c.

Fig. 9. A stop-cock with ball and socket, which, when adapted to a gas-light pipe, allows it to have an universal motion, so that the light may be turned in any direction.

Fig. 10. Section of the stop-cock, with ball and socket.

Fig. 11. Shows the ball and socket, fig. 9, in perspective.

PLATE IV,[26] fig. 1. _A Candelabrum_; the gas pipe ascending from the floor of the apartment, through the column _a_, and terminating in the burner of the lamp.

[26] The gas-lamps exhibited in this plate, are employed in the
library, counting-house, warehouse, and offices of Mr. ACKERMAN, and,
by whose permission, they are copied on this occasion.

Fig. 2. _A fancy pendent Cockspur Lamp._ The gas being transmitted to the burners, _c_ _c_, by means of the pipe, _a_.

Fig. 3. _A Pedestal Argand Lamp._ _a_, the pipe and stop-cock, which transmits to, and shuts off the gas from the burner of the lamp.

Fig. 4. _A Pedestal Cockspur Lamp._ _a_, the stop-cock and gas-pipe.

Fig. 5. _A fancy bracket Cockspur Lamp_, intended merely to show that the coal-gas, as it passes to the burner, is perfectly devoid of colour, and invisible. _a_ is a glass vessel furnished at its orifice with a brass cap, _c_, and perforated ball, out of which the gas-flame proceeds. _b_, the pipe which conveys the gas into the glass vessel, _a_.

Fig. 6. _A Bracket Argand Lamp._ _a_ and _b_, the gas pipe communicating with the burner.

Fig. 7 and 8. _A Horizontal Bracket Lamp._ _a_, the gas pipe, supposed to be concealed in the ceiling. _b_, the communicating pipe, which, together with _c_, branches out at right angles at _d_ _d_. _e_ _e_, are the burners of the lamp.

PLATE V. fig. 1. _A Candelabrum_, into which the gas-pipe ascends from the floor of the apartment, the lateral branches communicating with the central tube.

Fig. 2. _An Arabesque Chandelier._ The gas enters from the ceiling of the room into the rope-shaped pipe, _a_, from which it proceeds through one of the arched ribs, _b_ _b_, into the horizontal hoop, or pipe, _c_.

Fig. 3. _A Roman Chandelier._ The gas enters through the inflexible hollow chain, _a_, into the central tube, _b_, from whence the burners are supplied by the lateral branches, _c_ _c_.

Fig. 4. _A Gothic Chandelier._ The gas is transmitted to the burners through the rope, _a_, which includes a tube, and the communication with the burners is established through the lateral branches.

Fig. 5. _A Pedestal Figure Lamp._ The gas is here made to pass by means of a pipe through the body of the figure into the lattice-work _plateau_, constructed of hollow and perforated brass tubes.

Fig. 6. _A Pedestal Vase Lamp._ The gas-tube enters through one of the claw-feet of the altar-shaped pedestal, into the glass vase, _a_, at the bottom of which it joins the tubes communicating with the metallic corn-ears, _b_, at the upper extremities of which it forms _jets de feu_.

Fig. 7. _A Girandole._ The gas enters through the bracket, _a_, and is conveyed to the burners by the descending tubes, _b_ _b_.

Fig. 8. _A Candelabrum_, having a central pipe, through which the gas is conducted to the burner at the top.

OTHER PRODUCTS OBTAINABLE FROM COAL: NAMELY, COKE, TAR, ESSENTIAL OIL, &c.

Having thus far considered the nature of coal-gas as a substitute for the lights now in use, it will be necessary to attend more particularly to some other products which are obtained during the production of this species of light: namely, coke, tar, ammoniacal liquor, &c.

_Coke._--The substance called coke, which constitutes the skeleton of the coal, or its carbonaceous base, is left behind in the retort, after all the evaporable products have been expelled from the coal by heat.--See page 85.

It is sufficiently known, that coke is a more valuable fuel than the coal from which it is obtained.

Hence, immense quantities are prepared in the large way, but the gazeous and other substances are lost in the process employed for carbonizing the coal.[27] In the manufacture of coal-gas, the coke comes from the retort, enlarged in size, and greatly diminished in weight, when compared with the original coal. In whatever state the coal may be when introduced into the retort, the coke is uniformly taken out in large masses, so that the refuse coal, or dust, and sweepings of the pit, which are now thrown away, may be employed and converted into an excellent fuel. Coke is decidedly superior to coal for all domestic, and more especially for culinary purposes; the heat which it throws out being more uniform, more intense, and more durable. No flame, indeed, accompanies it, and it seldom needs the application of the poker,--that specific for the _ennui_ of Englishmen; but these deficiences are more than balanced by the valuable property of emitting no sparks, of giving more heat, and burning free from dust and smoke.

[27] The preparation of coke is as follows:--A quantity of large coal
is placed on the ground in a round heap, of from 12 to 15 feet in
diameter, and about two feet in height; as many as possible of the
large pieces are placed on their ends, to form passages for the air;
above them are thrown the smaller pieces and coal dust, and in the
midst of this circular heap, is left, a vacancy of a foot wide where a
few faggots are deposited to kindle it. Four or five apertures of this
kind are formed round the ring, particularly on the side exposed to
the wind; there is, however, seldom occasion to light it with wood,
for other masses being generally on fire, the workmen most frequently
use a few shovels of coal already burning, which acts more rapidly
than wood, and soon kindles the surrounding pile; as the fire spreads,
the mass increases in bulk, puffs up, becomes spongy and light, cakes
into one body, and at length loses its volatile parts, and emits no
more smoke. It then acquires an uniform red colour, inclining a little
to white, in which state it begins to break into gaps and chinks, and
assumes the appearance of the under part of a mushroom; at this moment
the heap must be quickly covered with ashes, of which there is always
a sufficient provision around the numerous fires, where the coke is
prepared.

That coke must give out more heat during its combustion than coal, will at once become obvious, when we consider that the quantity of matter which, in the combustion of coal is changed from a solid to a state of elastic fluidity, must necessarily carry off a portion of caloric, which then becomes converted in a latent state without producing heat, whilst the glow of the coke radiates caloric with an intensity unimpaired by any demand of this kind.

It is thus that coke, though somewhat more difficult of ignition than common coal, always gives out a more steady, a more lasting, and a more intense heat.

The only inconveniences that attend the use of coke is, that, as it consumes, it leaves much more ashes than common coal, charcoal, or wood; and these much heavier too, which are, therefore, liable to collect in such quantity as to obstruct the free passage of air through the fire; and further, that when the heat is _very intense_, these ashes are disposed to melt or vitrify into a tenacious drossy substance, which clogs the grate, the sides of the furnace and the vessels. This last inconvenience is only troublesome, however, when the heat required is very great. In ordinary heats, such as are produced by kitchen or parlour grates, the ashes do not melt, and though they are more copious and heavy than those of charcoal or wood, they do not choke up the fire, unless the bars of the grate be too close together.

The relative effects of heat produced by coke and coal are as follows:--

Six hundred pounds of pit-coal are capable of evaporating 10 cubic feet of water in 20 hours, and 430lb. of coke are capable of evaporating 17 cubic feet of water in 12 hours and a half.[28]

[28] In order to learn the relative effect of different kinds of fuel,
with regard to their capability of producing heat, chemistry teaches
that equal quantities of fuel alike expended, will raise the
temperature of a given quantity of water through the same number of
degrees; whence, by knowing the original quantity and temperature of
water, together with the quantity of fuel expended to raise the water
to the boiling point, the result sought may be expressed by stating
the quantity of water at 30 degrees, which would have been raised 180
degrees by one pound of the fuel employed; or in the form of a rule,

Multiply the quantity of water by the number expressing the degrees
actually raised; multiply the number of pounds of fuel expended by 180
degrees. Divide the first product by the latter, and the quotient will
express the water which would have been raised 180 degrees by one
pound of the fuel. Or equal quantities of water may be compleatly
evaporated under equal surfaces and circumstances, with the different
kinds of fuel, the nature of which is to be examined; the quantities
of fuel expended for that purpose give the relative effect of the
different kinds of fuel, with regard to their power of producing
heat.

The Earl of Dundonald has shown that, in the application for burning lime, a quantity of coke uniformly burns a given portion of lime-stone in one-third part of the time that the quantity of coal from which the coke had been made could do.

This effect is to be accounted for from having previously freed the coal, or rather its coke, from the moisture and the tar, which it sends out during combustion, and which condenses on the middle and upper strata of stratified limestone and coal in the lime kiln, and impedes the whole mass of materials from coming into a rapid and compleat ignition; because the greater the quantity of materials, and the sooner the whole is ignited, the better and more economically the lime is burned, both as to coals and time; the saving of which last is a material object, especially at lime-kilns where there is in the summer time a great demand for lime, the coke occasioning the kilns to hold a _third more lime_ at the _same time_.

In the art of making bricks, in the smelting of metallic ores, and the drying of malt, the advantages of coke over coal, are sufficiently known.

The following account given by Mr. Davis,[29] shows that the advantages that may be derived in the processes of burning lime, plaster of paris, and bricks, by means of coke, are greater than at first sight might be imagined.

[29] Philosophical Magazine, Vol. 33, p. 435.

“The coke obtained in the gas process is so valuable, that it appears inexplicable that men should not avail themselves of this mode of procuring light, to the almost total exclusion of all other methods now in use. As a landholder, placed among an industrious but wholly illiterate society of men, I have had the more opportunity of trying this species of fuel or coke, which I could not otherwise procure in this sequestered spot, at a tolerably cheap rate, for purposes to which it has not, as far as I know, been hitherto employed. I must tell you that I am my own lime-burner, plaster of paris baker, and brick-maker; and that in these processes of rural economy I have derived the greatest benefits from this species of fuel, which I now prepare at a cheap rate, although I waste almost the whole of the light of the coal gas intentionally. The coal which I employed formerly for the burning of limestone into lime, is a very inferior kind of small coal, called here Welsh culm. The kiln for burning the limestone into lime is a cup-shaped concavity, surrounded with solid brick-work, open at the top, and terminating below by an iron grate. It has a stone door that may be opened and closed for charging and emptying the furnace when required. This furnace I formerly charged with alternate strata or layers of small coal and limestone, the latter being broken previously into pieces not larger than a man’s fist, until the kiln was completely filled. The stone is thus slowly decomposed; the upper part of the charge descends, and when it has arrived at the bottom of the furnace new strata are super-imposed, so as to keep the furnace continually full during a period of 50 hours. The quantity of lime I procured with small coal formerly amounted to 85 bushels. The strata of coal necessary for the production of this quantity of lime require to be four inches thick, and the time necessary for calcination was, as stated already, 50 hours.

“On applying coke instead of coal, the produce of lime may be increased to nearly 30 per cent. from the same furnace, and the time required to effect the calcination of this quantity of lime-stone is reduced to 39 hours: it also requires _less attendance_ and _less labour_, and the whole saving, thus accomplished, amounts to more than 50 _per cent. on the lime-kiln_.

“I have lately also employed coke for the burning of bricks. My bricks are burnt in clamps, made of bricks themselves. The place for the fuel, or fire-place, is perpendicular, about three feet high. The flues are formed by gathering or arching the bricks over, so as to leave a space between each of a brick’s breadth; and as the whole of the coal, if this fuel be employed, must, on account of the construction of the pile, be put in at once, the charge of the bricks is not, and never can be, burnt properly throughout; and the interference of the legislature, with regard to the measurement of the clamp, is a sufficient inducement for the manufacturer to allow no more space for coal than he can possibly spare.

“If coke be applied instead of coal, the arches, or empty spaces in the clamp or pile, as well as the strata of the fuel, may be considerably smaller: the heat produced in this case is more uniform and more intense, and a saving of 30 per cent. at least is gained.

“In the baking my own plaster-stone I also employ coke. The calcination of the stone for manure I perform in a common reverberatory furnace, and the men who conduct the process (who are otherwise averse to every thing new) are much pleased with the steadiness of the fire, and little attendance which the process requires, when coke is used instead of coal.

“These are the few facts I wish to state, with regard to the useful application of this species of fuel, which, no doubt, hereafter will become an object of economy of incalculable advantage to individuals, if its nature be better understood than it is at present.”

The quantity of coke obtainable from a given quantity of coal varies according to the nature of the coal employed. One chaldron of Newcastle coal produced, upon an average, in the gas-light manufacture, from one chaldron and a quarter to one chaldron and a half of well formed coke. If the carbonization of the coal has been carried to its utmost point, the coke produced, has a brilliant silvery lustre. Such coke is excellent for metallurgical operations, because it stands the powerful blast of the bellows, but for culinary and other purposes of domestic economy, the carbonization should not be carried so far, because, the coke then produced, kindles more readily and makes a more cheerful fire.

_Coal-tar_, _Oil_, and _Pitch_.--Another, valuable product obtainable from pit-coal, is coal-tar.[30] This substance is deposited, in the purification of the coal-gas, in a separate vessel destined to receive it.

[30] In the year 1665, Becher, a German chemist, brought to England
his discovery for extracting tar from coal, this distillation he
performed in close vessels. It is not mentioned in the records of the
time, whether Becher obtained, or rather collected, any other articles
than the tar.

The coal-tar is so called from its resembling common tar in its appearance, and most of its qualities.

Several works have been, at different times, erected both in England and on the continent, to procure from coal a substitute for tar; but they turned out unprofitable speculations. In 1781, the Earl of Dundonald invented a mode of distilling coal in the large way, which enabled him not only to form coke, but, at the same time, to save and collect the tar. Even this process however, for which a patent was taken out, has gained very little ground. Its object was still too limited; for though some of the ingredients of coal were procured, they were procured at an expense that nearly balanced the profits; and no attention whatever was paid to the coal gas, which constitutes the most important part of coal.

Coal-tar may be used with advantage for painting and securing wood that is exposed to the action of air or water. The wood being warmed, the tar is applied cold, and penetrating into the pores, gives the timber an uncommon degree of hardness and durability.

One chaldron of Newcastle coal produces in the gas-light manufacture from 150 to 180lb of tar, according to the circumstances under which it is produced. See page 94.

The tar obtained from Newcastle coal-tar is specifically heavier than that produced from cannel-coal; hence it sinks in water, whereas the latter swims on the surface of that fluid.

To render the tar fit for use, it requires to be evaporated to give it a sufficient consistence. If this process be performed in close vessels, a portion of an essential oil is obtained, which is known to colourmen by the name of oil of tar. To obtain this oil, a common still is filled with the coal-tar, and, being properly luted, the fire is kindled and kept up very moderate, for the tar is very apt to boil up in the early part of the process. The first product that distils over is principally a brown ammoniacal fluid, mixed however with a good deal of oil. As the process advances, and the heat is increased, the quantity of ammoniacal liquor lessens, and that of oil increases, and towards the end of the distillation the product is chiefly oil.

The oil and ammoniacal water which distil over do not mix, so that they may be easily separated by decantation. The oil is a yellowish inferior kind of oil of turpentine, which is very useful in painting ships, for making varnishes, and other coarse out-door work.

Two hundred pounds of tar produce, upon an average, fifty-three pounds of essential oil.