PART XII.

[49]Copied from Messrs. Clegg’s and Crossley’s printed directions to workmen, for fixing governors and gas metres.

The governor must be fixed perpendicularly, so as to admit its floating vesselu,x,y,z. Fig. 4,plate III., or fig. 9,plate III., to be taken out of the outer case of the machine if occasion should require it.

The gas enters into the machine from the street mains at the lowest brancha, and passes out of the machine by its highest branchb.

In connecting the pipes of supply, particular care must be taken that the work is notbound, or the governor by any means rendered leaky. It must be filled with water to the top of the central tube.

Examine the workmanship of the machine to see that it is perfect, and that the regulating coneP, is firmly secured to the top of the floating vessel and well centered. The floating vesselsu,x,y,z, should clear the sides of the outer case of the apparatus by a quarter of an inch; and when sunk down, it should rest even upon the top of the central pipe, which conducts the gas into, and out of, the machine. The aperture in which the cone moves will then be at its widest opening, and when the floating vesselu,x,y,z, has risen to its highest elevation, the regulating aperturex, T, will be closed.

In this situation particular attention must be paid, that the regulating cone does not stick or rub in any part, but that it descends freely.

To the lower extremity of the floating vesselu,x,y,z, may be adapted an air vessel for the purpose of reducing the pressure of the gas.

The governor must be so fixed, that the water which may condense in the pipes leading to the burners shall drain back to the street mains, in order that it may not accumulate in the machine so as to impede its operations; for this purpose the gas pipes should have a fall of half an inch in three or four feet.

When the locality of situation will not admit of the water that may accumulate in the pipes falling back to the mains, its accumulation within the governor above the proper level of the water is prevented by an inverted siphon affixed to the machine, which allows the water to drain off without any escape of the gas.

The governor must be firmly fixed to the nearest beam or wall, as the least vibration will render the lights connected with it unsteady.

When a situation cannot be obtained sufficiently warm to prevent the water from freezing, the machine must then be wrapped round with woollen cloth, or any other bad conductor of heat. The cellar where the gas enters the house, has generally been found the most convenient situation.

For supplying any deficiency of water which the governor may require; a small funnel with a curved tube is placed for this purpose at the top of the governor. When the governor is filled to its proper height, the water will begin to run out of the siphon.

The mode of regulating the height of the flames will be stated presently.

Fig. 11,plate III., exhibits a portable governor or regulating guage, combined with a gas metre in one case. A, is the inlet pipe which conveys the gas into the machine, and B, is the pipe leading from the governor to the lamps or burners. D, a label expressing the quantity of gas discharged by one revolution of the wheel, and the number of lights which the metre is capable of supplying when the pressure of the gas in the inlet pipe is of a density sufficient to support a column of water of half an inch in height.

In those situations where the pressure of the gas is equal in density to support only a column of water one-quarter of an inch in height, a metre of a larger capacity must be adopted for supplying the same number of lights; and if the pressure of the gas be equal only to support a column of water one-eighth of an inch in height, the capacity of the metre must be still larger, and thus the capacity may be increased so as to equal every pressure that may occur. The index which registers the number of revolutions, and consequently the quantity of gas which passes through the metre, is shut up in the projecting case, near H, furnished with a lock and key.

Previously to the gas metre being filled with water, ascertain that the regulating cone is screwed perfectly air tight into the top of the floating vessel which receives the gas, and that the regulating aperture in which the cone moves, together with its spindle and guide rods, work perfectly free and without friction. Raise the floating vessel to its highest elevation, thereby closing the regulating aperture suddenly with the cone; in this situation it must not rub when turned and tried on every side, but descend with the least friction.

The gas metre and regulator being thus examined and fixed, the machine may be supplied with the requisite quantity of water in the following manner:

Open the stop-cock which admits the gas into the machine; open also the aperture E, which serves to show the pressure of the gas in the machine, and likewise the opening G, which lets out the air whilst water is poured in at the aperture H. The superfluous quantity of water will run out by the siphon tube at K.

Pour water also into the governor until it runs out at the aperture at M; and when this has beenaccomplished, till the gas metre with water at the opening H, until it overflows at the aperture K, when the surface of the water will appear at the cypher line on the scale board. The apertures F, G, H, K, and M, may then be closed, and the machine is ready for action.

Near to N, is an aperture communicating with the stuffing box in which the axis of the machine moves, and through which it should occasionally be supplied with a small portion of melted tallow.

To adjust the height of the gas flames of the burners, so that they be all uniform, open the stop-cock which admits the gas into the metre, and open also the stop-cocks of the burners, and as soon as the air has become discharged by means of one or two revolutions of the metre, light all the burners. Adjust the height of the flames in the first instance by their stop-cocks, that they become all of an equal height, which should be about double the diameter of the flame; if any of the flames be too low when the stop-cock is fully open, a small weight must be placed upon the top of the floating vessel of the regulator, sufficient to produce the required flame at the burner, and then again adjustthe remaining lights by their stop-cocks as before stated; this being done, the aperture to which each burner is screwed must be sufficiently narrowed, that it will admit no more gas than is requisite for the required height of the flame, when the stop-cock is fully open. The diminution of the aperture of the stop-cock may be effected by a brass plug fitted into it, with a hole in its centre, which must be gradually widened with a drill until the flame has required the proper height. It is recommended, instead of adding weight to the floating vessel of the regulator, that the tubes which supply the gas be sufficiently capacious to render the weight unnecessary.

The burners should also be examined from time to time. Observe that the plugs, sockets, and every other part of the gas metre and regulator be air tight, and that there be no escape of water or gas.

An escape of gas, either from the metre or from any of the tubes or burners, will be discovered by looking at the index of the metre, as the wheel cannot fail to move whenever there is an escape of gas, if the stop-cock is open which supplies the gas to the metre. The place where the gas escapeswill be found in the usual way, either by the odour which the gas produces, or by passing a lighted taper over the apertures and connections of the metre, and along the tubes leading to the burners, which will cause the gas to take fire at the place where the leak happens to be.

The following remarks will assist the workmen in correcting any irregularities which may occur in the lights connected with the apparatus.

A diminution, or extinction of the lights, may be occasioned by a deficiency of water in the gas metre or regulator; when this occurs the necessary quantity of water must be supplied as before directed up to the cypher line on the scale board E, of the metre, and opening the aperture M, where it may be seen when the water has risen to the proper height in the governor.

A diminution of light may also be occasioned by some obstruction or contraction of the tubes which supply the gas, or by a diminution of the pressure of the gas in the mains, to which the metre was originally adjusted.

When the lights increase above their standard height, and are variable with the changes in thepressure or velocity of the gas in the mains or tubes of supply within the house or place, lighted, there is then reason to believe that the governor is not performing, which may arise from the following causes. Its floating vesselu,x,y,z, may have become fast by the friction of the spindle or guide rod, requiring cleaning, or by an accumulation of water in the air-vessel of the floating vesselu,x,y,z. The water may be drained off at a small plug by taking out the floating vessel. The same inconvenience would arise from a diminution in the proper level of the water.

In order to ascertain that the governor performs correctly, observe at the time of lighting or extinguishing any of the burners connected with it, that its floating vessel rises and falls every time the stop-cock is opened, and that the lights do not suffer any material change.

An instantaneous starting or dancing of the lights, is generally occasioned by an accumulation of water in the tubes through which the gas passes; if this should happen in the vicinity of the metre and governor, it may be drained off at the aperture K. A provision for a like purpose is alsomade at the bottom of the governor when detached from the metre.

In order at any time to ascertain the pressure of the gas in the metre, close the stop-cock which admits the gas, and open the aperture G and F, which will shew the level of the water on the scale board E. This being first observed, close the aperture G, and open the stop-cock, and the pressure of the gas in the metre will be indicated by the rise of the water on the scale board E, above its original height.

The name ofmains, is given in the strictest sense of the word, to the cast-iron pipes from two inches in diameter and upwards, placed under ground, for conveying the gas into smaller branch pipes; but in a more extended sense, the term is applied to every pipe from which smaller ramifications or branch pipes proceed.

All mains destined to convey coal gas should be proved, they should be submitted to the trial of sustaining a column of water 300 feet high, and the pipe should be rejected if the least moisture appears on any part of the side of the pipe whilst submittedto this trial. For although such a pipe may remain impervious to gas for some time, the imperfection or fissure which permits the water to issue through under such a pressure, speedily increases, in consequence of the moisture to which the main under ground must necessarily be exposed. A skilful workman who is in the habit of proving pipes will distinguish, with an astonishing degree of correctness, a faulty pipe, by the sound produced by blows of the hammer upon the pipe. The faulty part, when struck upon, produces a jarring sound very different from the clear sound which a blow of the hammer produces when the pipe is in a perfect state. By this means the workman also detects, by the ear, inequalities in the thickness of the metal of the pipe.

Fig. 14,plate V., represents a longitudinal section of two flanch pipes, and the mode of connecting them.a, andb, are the pipes with their flanches connected; they are joined together, and rendered air-tight, by first interposing between the flanches a coat of iron cement, and then screwing up the faces of the flanches by means of screw bolts and nuts.

The composition of the cement is as follows:

Take four ounces of flour of sulphur, and two of muriate of ammonia, and mix them intimately together. When the cement is wanted, take five ounces of the above mixture, and add to it six pounds of cast iron borings, and blend them intimately together in a mortar; wet the mixture with water, and when brought to a proper consistence, apply it to the joints with a wooden or blunt iron spatula.

A degree of action takes place among the ingredients and the iron surfaces to which it is applied, which at last causes the whole to unite into one mass. In fact, after a time, the mixture and the surfaces of the flanches become a species of pyrites (containing a very large proportion of iron) all the parts of which cohere strongly together, and form one mass. It is essential that no larger quantity of the ingredients of the cement should be mixed up with water, than is required for immediate use.

Fig. 15,plate V., represents a longitudinal section of a spigot and faucet pipe. These pipes are most commonly used as gas mains.a, iscalled the spigot,b, the faucet. The cavity between the inside of one, and the outside of the other, is partly filled with rope yarn, or oakum, and a good fitting of the two pipes being thus effected, melted lead is poured into the cavity, which when set, is hammered in by the end of a punch.

The inner parts of the faucet of these pipes ought to be no larger in diameter than just to fit the spigot. This supports the pipe, independently of the interposed lead and rope yarn, and prevents the risk of hurting the joint from any external stress. The inner faucet is commonly made about two and a half inches deep, and has the spigot inserted one and a half inch into it. The practice of some manufacturers is to make the outer faucet, or that which contains the lead six inches deep, for all pipes above six inches in diameter; and to make the faucets of all pipes below six inches, the same depth as the diameter of the pipes. It is usual to make the space for the oakum and lead all round the spigot, from one inch to one and a quarter inch; that width is required, in order that the lead may be firmly driven into the joint. When the spaceis very narrow, this cannot be done. On the other hand, when too wide, there is a waste of lead, and a risk of injury from the unequal expansion of the two metals.

All gas mains laid in public streets should be placed at least eighteen inches below the surface of the ground, to secure them from being disturbed by carriages, or interfering with the paving of the street; they should be placed perfectly firm, so that they may not easily give way.

The course of all gas mains should be rectilinear, with a dip of about one inch, in every ten feet distance.

In all wide streets, where the number of houses on both sides of the streets, to be supplied with gas, is numerous, it is more economical to employ a separate gas main for each side of the street, than to make use of one larger main for both sides; because smaller mains may then be employed, and the collateral branch pipes leading into the houses are shorter; these circumstances amply compensate for the additional main. Allbranchpipes proceeding from a main, should have a dip of about one inch in ten feet, towards themain from which they proceed, so that any fluid that may happen to collect in these pipes must run into the mains.

All small wrought iron branch pipes proceeding from the mains into the houses or places to be lighted with gas, should be covered with a thick coat of coal tar, before they are laid down into the ground; this may easily be done by heating the pipe, and laying on the boiled tar with a brush.

Every separate length of branch pipe should be tried by condensing the pipe under water, in order to be certain that the pipe is sound. The junctures of these pipes should be made by dipping the male screw of the pipe into a mixture of white lead and linseed oil, before they are screwed together.

Notwithstanding the usual care which can be taken in proving pipes, before the gas is admitted into them, a slight leakage may be sometimes subsequently detected.

Therefore, before the gas is suffered to enter the mains, they should be again proved, in order to be certain that all the junctures are air tight.The most convenient manner of proving the mains when laid, is by means of a small portable gas holder filled with common air, and connected by means of a small pipe, with the system of the mains to be tried. This gas holder should be made to act with a pressure at least four times greater than the pressure which the pipes will have to sustain by the gas they are to convey. If the mains are air tight, the gas holder will remain stationary, but if they are not sound, the gas holder will descend, in proportion to the leak of the mains, the quantity of gas lost may be thus ascertained.

Every quarter of a mile of pipe should thus be tried separately. In this manner we become also enabled to detect instantly, whether any collateral branch pipe has been left open by the workmen, a neglect by no means uncommon in this department of the gas light business.

In order to guard against the danger of water entering from the external surface into the pipes, a reservoir should always be placed at the lowest point, where two or more descending mains meet and form an angle, so as to receive the waterthat may happen to collect at this angular point, an accumulation of which would cut off the communication between the two pipes; this reservoir is usually called a siphon, seepage 221. It ought to be at least twice the diameter of the bore of the mains, between which it is interposed, and four times that diameter in depth. These reservoirs afford the best indication to show the sound or leaky state of the system of the mains. In all instances where the pipes are perfectly sound, observation has shown, that half a mile of gas mains, three inches in the bore, does not deposit more than a quart of water in a year; on the other hand, if the mains are leaky, the water of the reservoir requires to be pumped out, sometimes as frequently as every fortnight, and during wet weather, much oftener. The loss of gas by such leakage is much greater than is generally imagined. Instances might be mentioned where, in order to keep the common air out of a system of faulty pipes, a constant influx of gas which a pipe two inches in diameter can supply has been found necessary, and this of course is just so much gas lost to the economy of the establishment.

With regard to the diameter of the mains, no general rule can be given. It must vary according to the number of branch pipes and lamps which the main has to supply within a given distance,—the angular direction of the mains,—the pressure of the gas holder, and above all, with the relative altitude of the place where the gas holder is situated, and the place at which the gas is to be supplied, or where the lamps are placed. Indeed this is one of the most important considerations with regard to the economical distribution of gas mains, and by attending to this circumstance, a prodigious saving may be effected.

If the gas flows through a main placed at an altitude of the gas holder, and with a pressure to support a column of water half an inch high, this gas at an altitude of 100 feet, will support a column of water11⁄10inch high, and as the velocity of the gas is as the2√ of the height, or pressure, the quantity of gas which will flow through a given opening at an elevation of 100 feet, will be very nearly in the proportion of two to three. Hence if a gas burner, or gas lamp, produces a flame two inches high, at a place situated on a level with the base of the gasholder, the lamp, if supplied by the same main, but situated 100 feet higher, will burn with a flame three inches high.

This important fact may be rendered obvious in the following simple manner:

Take a tube ten or fifteen feet long, and one inch in diameter, place it horizontally; let one end of the tube be open, and close the other with a plate pierced with a hole, of about1⁄32of an inch in diameter, and then fill the tube with gas. If a lighted taper be applied to the hole, when the tube is lying horizontally, the gas will not take fire; but on raising the end of the tube where the small aperture is, the gas will take fire, and the magnitude of the flame will become enlarged in proportion as the tube approaches towards the perpendicular.

Hence the diameter of gas mains must be varied, according to the altitude of the place to be supplied with gas. And it is in consequence of neglecting this principle that we observe so frequently certain parts of large towns scantily supplied with gas, whilst other parts furnished from the same mains, situated considerably above the level of the gasholder, have the gas in the greatest profusion, but at the expense of those places situated at a lower level. And so true is this, that if a main were to descend 100 feet below the base of the gas holder, and if the pressure of the gas in the main was only equal to sustain a column of water half an inch in height, the gas lamps could not be lighted at all, at a point so low, because the pressure of the gas is then in an equilibrium with the pressure of the atmosphere. Hence in lighting a town or district with coal gas, the best situation for the gas apparatus, as far at least as it regards the economy of the mains for distributing the gas, is the lowest part of the town or district. For if the mains are placed at an elevated situation, they require to be proportionally larger, and if situated at a lower place than the level of the gas holder, they must be smaller; but in either case the mains must bear a proper proportion to each other, according to the conditions and circumstances already stated, and it is here, where the skill of the gas light engineer becomes conspicuous, for the saving that may thus be effected in the lighting of a district or town with gas, is very considerable.

The requisite pressure of the gas for different situations with regard to the altitude of the place to be lighted, may be readily known by ascertaining the altitude of the place by means of the mountain barometer. The Englefield mountain barometer is most commodious and suitable for that purpose. This instrument is not liable to be out of order, it may be used by a single observer, and affords an easy method of ascertaining the elevations and depressions of the surfaces of the earth with the greatest facility, and to a degree of precision, that may vie with trigonometrical mensuration. Thus supposing the pressure of the gas at the level of the gas holder to be equal to a column of water half an inch high, by inspecting the height of the barometer, the requisite pressure of the gas at that place may readily be found.

That part of a gas main which does not supply any gas to a branch pipe or lamps, as it proceeds in its course need only be a quarter of the capacity which is necessary at the part where the branch pipe or pipes commence. For no inconvenience can arise from the increased velocity which thegas must assume in proportion to the diminution of the bore of the main, provided that the velocity of the gas is lessened by passing into a main of a greater bore, prior to it being conveyed into the pipe or pipes immediately connected with or supplying the lamps. The enlargement of the pipes should be in the proportion to the diameter of the two pipes, as four to one.

In order to avoid that the gas mains deposited under ground in public streets or other places, may not be on the one hand superfluously heavy, or as it is calledthick in the metal, and consequently unnecessarily expensive, and on the other hand not too light, or too thin in the metal, so as to be liable to become injured, we shall exhibit the weight of gas mains of different bores and lengths best suited for conveying gas, nowemployed at the best regulated gas works in the metropolis.[50]

[50]A mile of pipe of an average diameter, laid under ground ready for conveying gas, together with taking up and making good the pavement, costs in London, about £. 1000.—And in small towns where the lights are usually less clustered together than is the case in London, and where pipes of three inches in the bore are usually sufficient, a mile of pipe complete costs about £. 700.

The lamps or burners for the combustion of coal gas, may be infinitely and tastefully varied. The varieties commonly employed, are the Argand burner, the Cockspur burner, and the Bat’s Wing burner.

TheArgand burner, fig. 10, and 11,plate V., consists of two concentric brass tubes, about one and a half inch long, and seven-eighths of an inch in diameter, (the largest size burner employed.) The interval between the two tubes is closed at top and bottom. The upper part is closed with a ringof steel, it is perforated with fifteen or eighteen holes1⁄30of an inch in diameter. The gas enters into the cavity between the two tubes, and issues from the circular row of apertures in the steel ring at the top of the burner where it is burnt. A double supply of air within and without the flame is effected by means of the glass which surrounds the flame. The combustion of the gas is perfect when the admission of air is in due proportion to the magnitude of the flame. The height of the gas flame should never exceed three times the diameter of the flame. When the flame is too large, the light is less brilliant, and it then produces an odour, because the combustion is imperfect.

The best shape of the glass for surrounding the gas flame of the Argand lamp, is a straight tube, shown fig. 8,plate V., or a tube enlarged at the base, shown fig. 9,plate V.Fig. 10,plate V., is called a crutched argand gas burner, it is used for pillar lamps; fig. 11, is called a branch argand burner.

It is essential that the apertures for the emission of the gas of the argand gas lamp, be perfectly round and of an uniform size, without this conditionthe flame of the lamp is ragged, and not well defined.

Fig. 15,plate III., exhibits a swing bracket, furnished with acockspur burner. The burner consists of a hollow flattened globe, about half an inch in diameter, pierced laterally with three or more holes, of about1⁄30of an inch in diameter; out of these holes the gas flame issues in streams as shown in the sketch. With this burner the combustion of the gas is imperfect, and it is a wasteful mode of burning coal gas. The surrounding holes of the cockspur burner, was it not for the upward current of air, would give flames radiating in straight lines from the centre of the burner, but the ascending current of heated air, causes them to curve upwards like the spur of a game cock, and hence the name cockspur burner.

If the gas be made to burn from a series of holes made in the lateral circumference of a hollow flat cylinder, it will produce a circular horizontal series of flames curving upwards.

Fig. 12.plate V., is called abat’s wingburner; it consists of a small pear-shaped steel burner, about1⁄16of an inch in diameter, having a perpendicularslit at its upper extremity, about1⁄40of an inch in diameter. This burner exhibits a tulip-shaped flame, as shown fig. 13,plate V., it is well adapted for street gas lamps.

The stop-cock for admitting gas into gas burners should always be placed at least six inches from the burner. The stop-cock in the brackets, fig. 8, or 9,plate V., is placed ata.Pendant gas lamps, into which the gas is conveyed from a pipe above, through the ceiling, should be provided with a mercurial joint, or ball and socket joint. The former contrivance is preferable, because it can never leak;[51]but the latter requires occasional repairs. Fig. 14,plate III., shews the mercurial joint.a, is the pipe which brings the gas; it terminates in a sheet iron cup open at bottom, but closed air tight at the top; this cup is inverted into a small iron bason, containing mercury. D the iron tube which communicates with the gas lamp or burner, and the upper extremity of which projects above the surface of the mercury in the ironbason, whilst the other extremity proceeds to the burners or lamps.

[51]This contrivance has been adopted throughout the fitting up of the gas lights at the Royal Mint.

Swing bracket burners, fig. 13,plate III., should have the axis of motion at the joints A, A, A, perforated at right angles to each other, so as to admit the moveable joints at A, to be left open, without obstructing the passage of the gas when the bracket assumes different angular positions. All swing brackets ought to have a double, and not a single joint, because the latter soon wears oval in the two opposite edges; this is prevented by the double joint having an uniform bearing at top and bottom, it therefore can never leak.

Fig. 11,plate VI., exhibits the arrangement usually adopted for apendant perpendicular sliding lamp, or chandelier, which requires to be raised or depressed. This contrivance is convenient for lighting theatres, or public buildings, by means of a large central gas light chandelier, that may be raised or depressed at pleasure.

The gas enters into the tubeD, which is firmly fixed in the ceiling, as shown in the sketch; it passes through a hole near E, into a smaller tubej, which slides perpendicularly within thetube D. This sliding tube is made air tight by means of two stuffing boxes filled with oil, placed near B, and C. The sliding tubej, together with the chandelier suspended to it, is counter-balanced by a weight concealed in a box W, connected with pullies in the usual manner, as shown in the sketch, so that the chandelier may be raised or lowered at pleasure.

The adapting gas pipes to the interior of houses, for the supply of gas, simple and easy as it may appear, has been the means of not a little contributing to bring the gas light illumination, on many occasions, into disrepute. It has required years to enable workmen of the best intention to acquire sufficient practical skill in the proper execution of a business, which must be pronounced to constitute an art entirely new, and in which no progress could be made, but after having committed many errors. A house neatly and judiciouslyfitted up with gas pipes, displays to a person experienced in this art, a skill and judgment, equal to what is established in any other branch of mechanical employment. It must be obvious, that the art of arranging the pipes and adapting them, is one of that class of operations in which it is a real saving to employ the best materials and skilful workmen, to avoid repairs and subsequent alterations and derangements of the work. The supply and distribution of the pipes, or thefitting up, as it is called by the workmen, may be done almost at any price with regard to workmanship and materials, and to bargain for cheapness in the execution of it, with a faithful, honest, and skilful workman, must naturally be a losing concern to the person for whom the work is done. The cost of furnishing and adapting the pipes to one place, cannot serve as a standard for any other place, every separate place may present difficulties which could not be foreseen at the commencement of the work.

The stopping up and corrosion of the gas pipes, which at the commencement of the introduction of the new lights was complained of in manyplaces, it is now sufficiently established, originated entirely from the impurity of the gas, together with a faulty arrangement of the pipes, in consequence of which, the water of condensation accumulating in certain parts, exercised a strong chemical action on the copper pipes, and if the gas was not very pure, ultimately corroded the pipe. These objections do no longer exist, and it may safely be pronounced, that pure coal gas produces no action whatever on the copper tubes through which it is conveyed. In proof of this statement, we need only refer to the several districts of the metropolis, fitted up with gas pipes at the first introduction of the new lights, (1809,) all of which are still in perfect preservation.

It is perhaps unnecessary to add, that no pipe capable of being melted by a gas flame, should ever be employed for conveying or distributing gas through the interior of houses, because the facility with which such pipes might be perforated, could lead to serious consequences, if the gas issuing from the aperture of the pipe were lighted, the flame in that case would follow the melted part, through the whole extent of the pipe, and the hazard byfire would be considerably increased. Therefore, pewter, lead, and tin pipes, are very improper for distributing gas through the interior of houses, and should never be used for that purpose. Hence copper, and iron pipes, are universally employed.

In order that the pipes for conveying the gas from the mains, and distributing it through the houses or other buildings to be lighted with gas, may in the first place not be unnecessarily large, or too small, the following rule may serve as a guide to workmen:

One gas lamp,—consuming four cubic feet of gas in an hour, if situated twenty feet distance from the main which supplies the gas, requires a tube not less than a quarter of an inch in the bore.

Two lamps,—30 feet distance from the main, require a tube3⁄8of an inch in the bore.

Three lamps,—30 feet distance from the main, require a tube3⁄8of an inch in the bore.

Four lamps,—40 feet distance from the main, require a tube1⁄2inch in the bore.

Six lamps,—50 feet distance from the main, require a tube5⁄8of an inch in the bore.

Ten lamps,—100 feet distance from the main, require a tube3⁄4of an inch in the bore.

Fifteen lamps,—130 feet distance from the main, require a tube 1 inch in the bore.

Twenty lamps,—150 feet distance from the main, require a tube 11⁄4inch in the bore.

Twenty-five lamps,—180 feet distance from the main, require a tube 15⁄8of an inch in the bore.

Thirty lamps,—200 feet distance from the main, require a tube 11⁄2inch in the bore.

Thirty-five lamps,—250 feet distance from the main, require a tube 15⁄8of an inch in the bore.

All copper pipes employed to convey gas through the interior of houses should be of the following weight, with regard to a given length of the pipe:

No coppered pipes should be used but such as have wrapt over and brazed joints. They should be well annealed, to render them pliable without being liable to break.

All the bends for connecting pipes must be circular, see fig. 22,plate V.

No branch pipe ought to proceed from a pipe of a quarter of an inch in the bore, and no more than two branch pipes should proceed from a pipe three-eighths of an inch in the bore.

All branch pipes before they are fixed for conveying gas, must be proved by condensing air into them by means of a condensing hand pump. The pipe should be placed in a trough of water, the leak will then be easily observed by the air bubbles which rise through the water whilst the air is condensed in the pipes.

All branch pipes should have a rectilinear course; pipes that are twisted have an unsightly appearance.

All pipes should have a descent of no less than a quarter of an inch in four feet.

The seams or brazed part of the pipes must always be out most and not towards the wall;because if a leak should happen to take place in the brazed part of the pipe, it may then be easily discovered and more readily repaired.

When all the pipes have been furnished to a house or place intended to be lighted, the whole system of the pipes should be examined with the utmost rigour, to ascertain whether all the junctures are air tight. This should be done by condensing air into the pipes by means of a condensing syringe, and if the piston of the syringe lowers after condensation, it is a sure indication that the pipes are faulty, and consequently totally unfit for receiving the gas. The leak may be detected by passing a lighted taper carefully along the whole extent of the pipe filled with condensed air, when the flame of the taper will be affected as it passes over the faulty place of the pipe.

The aperture from which the gas can escape may however, be so small, as to render it a matter of difficulty to discover it in the manner just stated; but when the pipes are filled with coal gas, the escape of it, when all the stop-cocks of the lamps and burners are shut, will soon become obvious, by the peculiar odour of the gas,if the apartment, or place, where the pipes are placed, is suffered to be closed for about twenty-four hours. The gas should not be introduced into pipes in which any defect of this kind is found, until it be completely removed. The most severe trial to ascertain the air tightness of any system of pipes is, the trial by exhaustion, by means of an air pump, for the guage of the pump will discover the minutest leak, which the preceding method of proving pipes can not discover.

All pipes after being proved should be painted of the same colour as the surface to which they are affixed.

The whole system of pipes should incline to one or more places, so that any moisture that may happen to accumulate in the pipes, may collect at such places, whence it may be readily removed by opening a screw plug adapted for that purpose.

All the different junctures of mains and branch pipes, should be effected by means of connecting pieces, so that any part of the system of the pipes, or any separate branch pipe may readily be detached,and put up again if occasion should require it; fig. 19,plate V., exhibits this mode of connecting gas pipes by means of union joints. A, B, C, D, E, shows a gas pipe with its union or connecting joint, divided into its separate parts.D, is a collar of leather, which passes over the part C, of the union joint, close up to the shoulder of the joint; the opposite extremity of the pipe may be inserted into the socketB, so that the shoulder C, comes in contact with the fillet or rim in B, to prevent it passing over the shoulder C, when B and E are screwed together. The latter part of the pipe is furnished with a male screw to correspond with the thread in the collar B. The shoulder piece C, is of rather a larger diameter than the bore of the tube A, with which it is to be connected. The short piece E, furnished with a male screw, is of the same diameter as the part C. The pieces C, and E, of the pipe are soft soldered, one to the tube A, and the other to the tube E, but previous to soldering on C, it is necessary that the socket should be inserted into the tube A, it will then be ready for connecting, as will become obvious byinspecting fig. 20, which shows the various parts of the union joint fitted for use. It is evident that if the extremity D, in the pipe B, be brought close to the pipe E, and if the socket C, be moved along the pipe A, and screwed upon the male screw at D, as far as it will go, the face of the part D, must press close against the leather collar which is placed on E, and render the joint gas tight. These kind of joints are very convenient for circular bends, fig. 22, and T, pieces, fig. 21. The T pieces, fig. 21, are very useful for collateral branch pipes, either for the same or of a less diameter as the pipe, from which they proceed, so as to branch off at right angles.

Fig. 22, is a quarter circular bend; it is convenient for adapting tubes along the angular parts of rooms, and to all such situations where the tube is to have a sudden circular course. Small copper tubes may be readily bent to the required angle without breaking, but if a tube should terminate in any angular part of a room, in that case a circular bend furnished with a male and female screw, is convenient for connecting the pipes together.

All pipes adapted to the exterior of buildings, should be kept a little distance off from the wall, to prevent the wet lodging between the pipe and the surface to which they adapted.

Sheet iron mains for the interior of houses, are preferable to copper mains, provided the course of the main with regard to the position of the branch pipes, does not require too many angular directions, or circular bends.

The illuminating power of coal gas, differs according to the nature of the coal from which it is obtained, and the manner in which it is purified, together with the quantity of naptha or essential oil chemically combined, or mechanically suspended in the gas. For if the gas be strongly agitated with water, its illuminating power is diminished. Coal gas, which abounds in olifiant gas or supercarburetted hydrogen possesses the greatest illuminating power, and hence carburetted hydrogen obtained from the decomposition of coal tar possesses a greater illuminating power than thegas obtained from the coals which produced the tar. The illuminating power of carburetted hydrogen obtained from coal tar when compared to the gas obtained from the best Newcastle coal is in the proportion as six to five. In fact the intensity of light evolved during the combustion of gazeous bodies composed of carbon, hydrogen, and oxigen, is always in the ratio of the quantity of carbon contained in equal quantities of the gazeous compound, and hence the gas from animal oil which is chiefly composed of supercarburetted hydrogen or olifiant gas, surpasses in illuminating power the gas obtained from coal.

Half a cubic foot of coal gas, obtained in the ordinary way of manufacturing coal gas, from Newcastle coal, is equal in illuminating power and duration of time, to the light produced by a tallow candle six in the pound, burning for one hour, and as such a tallow candle lasts five hours, therefore fifteen cubic feet of coal gas, are equal in value with regard to illuminating power to one pound of candles. And as 112 pounds of Newcastle coal produce by the new method of manufacturing coal gas, at least 550 cubic feet ofgas, therefore the quantity of gas produced from a chaldron of Newcastle or Sunderland coal, (the minimum weight of which is 27 cwt.) is equal in illuminating power to 1000 pounds of tallow candles.

The illuminating power of coal gas may readily be ascertained. Though the eye is not fitted to judge of the proportional power of different lights, it can distinguish in many cases with sufficient precision where two similar surfaces are equally illuminated. As the lucid particles emitted from luminous bodies are darted in right lines, they must spread uniformly, and hence their density diminishes in the duplicate ratio of their distance. From the respective situations, therefore, of the centres of divergency, when the contrasted and illuminated surfaces become equally bright, we are enabled to compute their relative degrees of intensity. And for this purpose it is assumed as a principle, that the same quantity of light, diverging in all directions from a luminous body, remains undiminished in all distances from the centre of divergency.

Thus we must suppose, that the quantity of lightfalling on every object, is the same as would have fallen on the places occupied by the shadow; and if there were any doubt of the truth of the supposition, it might be confirmed by some simple experiment.

Therefore, it follows, that, since the shadow of a square inch of any surface occupies at twice the distance of the surface from the luminous point the space of four square inches, the intensity of the light diminishes as the square of the distance increases. If, consequently, we remove the two sources of light to such distances from an object that they may illuminate it in equal degrees, we are authorized to conclude that their original intensities are inversely as the squares of the distances.

Hence, if two lights of unequal illuminating powers shine upon the same surface at equal obliquities, and an opaque body be interposed between them and the illuminated surface, the two shadows produced must differ in blackness or intensity in the same degree. For the shadow formed by intercepting the greater light, will be illuminated by the smaller light only; and reversely, the other shadow will be illuminated by the greater light;that is to say, the stronger light will be attended with the deeper shadow.

Now it is easy by removing the stronger light to a greater distance, to make the shadow which it produces equal to that afforded by the less light. Experiments of this kind may be made in the following manner:

Fasten a sheet of white paper against the wall of a room, and place the two lights intended to be compared, so that the rays of light from each fall with nearly the same angle of incidence upon the middle of the paper. In this situation, if a book or other object be held to intercept part of the light, which would have fallen on the paper, the shadows may be made to appear as in this figure:

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