[38] This machine has been adopted at the gas works at Chester, Birmingham, Kidderminster, Bristol, and in many other provincial Gas Establishments.
The lime trough is also made moveable on a centre or axis, in such a manner that it may readily be inverted by a lever from the outside, for the purpose of emptying its contents into the bottom of an exterior vessel, from which the waste materials may be discharged at pleasure.
With this machine we are farther enabled to employ the purifying mixture in a semi-fluid state, and consequently in a much less bulk; and after having suffered it to remain in the reservoir destined to receive it, the waste substance speedily acquires such a degree of solidity that it may be dug out with a spade and carted away in a small compass. The safety of the apparatus is therefore insured and the construction of expensive drains and sewers is rendered unnecessary. The following description will render the construction of the improved apparatus obvious.
A, A, fig. 2, plate II., is a rectangular four-sided prism, made of cast-iron plates, screwed together air-tight with bolts and cement. The base of the prism terminates in a rectangular four-sided pyramid placed with its apex downwards. It is surrounded by an iron stage, supported upon pillars, as shown in the design.
Within this vessel, which in fact composes only the outer case of the apparatus, is contained an oblong trough B, fig. 2, plate II., (it is shown in the design as if broken down), moveable upon an horizontal axis, fixed to one of its longest sides, so that by means of the wheel C, or lever communicating with the axis, and applied on the outside of the machine, the trough B, may be inverted, and its contents discharged into the exterior case, or lower part A, A, of the machine. The part B, of the machine is called the lime trough, because it is destined to contain the quick-lime and water, by means of which the crude coal gas is purified. Within this trough B, is inverted an oblong rectangular box D, closed at top and open at bottom, called the air-box, because it receives the gas to be purified.
In each of the longest sides of the box D, are perpendicular openings or slits (as shown in the design) exactly opposite to each other. Through the whole length of this box D, passes a horizontal axis furnished with as many teeth or claws as there are upright openings, through each side of the box. These claws extend a little way through the openings so that when the axis, which passes through a stuffing box, is made to revolve by means of the handle X, the ends of the claws pass through the openings and scrape them out every time the axis is turned. The claws operate first on the openings of one side of the box and then on those on the opposite side. They pass quite through and therefore keep them clear; those parts of the claws which enter into the openings are narrow in the direction of their motion, and that part of each claw which is nearest to the centre, is broad and flat, hence they act as paddles or rowers whilst they are in motion, to stir up the quick-lime and water.
Fig. 10, plate III., represents a transverse section of this part of the apparatus. B, B, is the lime trough; D, the air box inverted into the lime trough; the dotted circle shows the sweep of the claws when the shaft is put in motion. The darts show the course of the gas.
Fig. 10, plate VI., represents a plan of the machine. G, shows the inverted air-trough with its axis, and the claws or teeth fixed upon the axis. H, is the lime trough. A, the outer case of the machine; R, R, the axis, to which is affixed the wheel or lever, for inverting the trough H. L, the axis and handle to give motion to the shaft upon which the claws are fixed, for stirring up the contents of the lime trough.
The inverted air-box D, fig. 2, plate II., is supported within the outer case of the machine A, A, fig. 2, plate II., by cross bars, and the axis is put in motion by the handle X, on the outside of the machine. It is rendered air-tight by a stuffing box, and is provided with wheel-work, as shewn in the design, fig. 2, plate II., to communicate the motion to the axis.
The gas is brought into the air box by the pipe N, fig. 3, which proceeds from the tar vessel, fig. 3, plate II. The gas cannot escape out of the machine without displacing the column of fluid in the lime trough, in order to make its way through the openings or upright slits in the side of the air box D, and thus bubbling up through the mixture of quick-lime and water, the depth of which is one foot. The sulphuretted hydrogen and carbonic acid being thus made to combine with the lime, the carburetted hydrogen is left more or less pure, it is conveyed into the gas metre, by the pipe V, where it is to be measured, and from thence by the pipe W, fig. 4, into the gas-holder.
When the purifying mixture is to be removed, the workman unbolts the wheel C, fig. 2, and turns it half way round; (if the emptying of the lime trough requires more power than can conveniently be applied by means of the wheel, the axis of the trough may be worked with a tooth and pinion, a small wheel being attached to the axis of the pinion as a perpetual handle;) this motion inverts the lime trough B, and its contents become discharged into the outer case forming the inverted pyramid of the apparatus, whence the waste materials may be conveyed into the reservoir or pit Q, by drawing open the sliding valve o, fig. 2, plate II., or o, fig. 3, plate VII., added for that purpose to the discharging pipe P, fig. 2, plate II., or p, fig. 3, plate VII. To prevent the air entering into the machine when the waste lime is discharged, the lower extremity of the outlet pipe P, dips into the basin Q, fig. 2, plate II., which always contains a portion of the waste fluid and thus seals the extremity of the pipe P.
One side of the lime-machine is provided with two large lenses, to admit light into the interior of the apparatus, so that by means of an eye-glass fixed in a proper place, the workman is enabled to see into the interior of the apparatus. And when the machine requires to be cleaned out, the manhole as it is called, is opened for the workmen to enter into the apparatus to remove any solid incrustation of carbonate of lime, or hydrosulphuret of lime that may happen to be formed in the lime trough, or any other part of the apparatus.
The wheel C, is loaded with a counter-weight, to balance the weight of the lime trough. To bring the lime trough again into a proper position, to be re-charged with a fresh portion of the purifying mixture, the workman turns the wheel C half round, the contrary way to that which caused the trough to be turned topside-down, and the trough may then be re-filled with a fresh portion of lime and water from the reservoir R, fig. 2, plate II., (or R, fig. 3, plate VII.,) containing the mixture ready prepared. Y, is a pipe to bring water from a cistern into the lime reservoir R. The prepared lime which is to supply the machine is put into the vessel R, and a sufficiency of water being mixed with it, the mixture is stirred up to the consistence of a semi-fluid mass.
T, shows the pipe furnished with a sliding valve S, for conveying the purifying mixture of quicklime and water into the lime trough from the reservoir R, which is furnished with an agitator to stir up its contents.
To give motion to the shaft for stirring up the contents of the lime trough D, the inventor of this machine (Mr. Clegg,) has happily applied the gas, to act as a power for that purpose. This operation will be explained hereafter in describing the gas metre.
The pipe N, which conveys away the purified gas, proceeds from an hydraulic valve, to cut off the communication between the gas holder and the lime machine, if occasion should require it, and to prevent the gas from passing back from the gas holder into the lime machine.
It consists of a box containing water into which dips a small pipe, by means of which the gas passes out of the lime machine, and from thence into the pipe V, communicating with the gas metre. The box is furnished with a tube curved upwards to discharge the water when it accumulates above the required height, and to prevent any quantity being thrown out of the hydraulic valve, by the concussion of the fluid in the lime trough.
One cubic foot capacity of the lime trough is sufficient to purify 1000 cubic feet of gas obtained from Newcastle coal in twenty-four hours.
The proper purification of the gas being a matter of essential importance, as already illustrated page 140, it becomes of great consequence to have some ready means of ascertaining whether the workman does his duty in this respect, by keeping the lime trough D, fig. 2, plate II., properly charged with the requisite quantity of lime and water necessary for the purification of the gas.
For this purpose an apparatus has been adapted by Mr. Clegg to the lime machine, which serves not only to indicate the quantity of fluid contained in the machine when gas is manufactured, but which also enables the workmen to appreciate the quantity of quick-lime necessary for the purification of the gas, and to ascertain its purity. The apparatus consists of a closed cup C, fig. 23, plate IV., partly filled with any coloured liquid. Into this cup is cemented, air-tight, a straight glass tube a, about 21⁄2 feet long and a 1⁄4 of an inch in the bore; the lower extremity of the tube nearly touches the bottom of the cup, and is therefore sealed by the fluid. d, d, is a small copper tube, which forms a communication between the air confined above the surface of the fluid in the guage cup C, and the gas which is proceeding into the lime-trough.
The communication may be established at any part of the pipe which conveys the gas into the lime machine. When the connection is made, the fluid in the guage cup C, will be driven up into the perpendicular measuring tube a, by the pressure of the gas, to an altitude equal to a column of liquid contained in the lime-trough. It is essential that the tube a, be at least 21⁄2 feet in height, if the depth of the lime-trough is one foot, for without this precaution, the fluid will rise out of the tube in consequence of the oscillation which it suffers. By this means the overseer of the works will be enabled, by mere inspection, to know whether the workmen have charged the lime trough with the mixture of quick-lime and water to the requisite height, which should never be less than from ten to fifteen inches. Because the abstraction of the sulphuretted hydrogen and carbonic acid gas, from the carburetted hydrogen with which it is combined, is greatly facilitated by pressure, and there is no inconvenience whatever in operating under a pressure of a column of fluid of even double the height that has been stated, provided the apparatus is properly constructed. From experiments made on this subject, I am justified in stating that one half of the quantity of quick-lime that is required for the purification of coal gas in the ordinary way, is sufficient, if the column of the liquid opposed to the gas is raised to twenty inches high, nor is the evolution of the gas in any degree retarded under such a pressure.
The curved tube d d, which is cemented air-tight into the gauge cup c, has a free communication with the gas in the guage cup c. It serves to enable the workmen to form some notion of the chemical constitution of the crude gas, before it passes into the lime machine. For if the stop cock e of the tube be opened, and the descending leg a of the bended tube d be immersed in a glass containing a solution of super acetate of lead, some notion may be formed by a little practice of the quantity of lime requisite for the purification of the gas, from the quantity of (black precipitate) hydrosulphuret of lead produced. Two per cent of quick-lime to the coal employed (if Newcastle coal) is usually sufficient for the complete abstraction of all the sulphuretted hydrogen and carbonic acid, contained in the crude gas, provided the operation be carried on under a pressure of not less than a column of water twelve inches in height.
The test tube f, properly so called, may be adapted to any part of the pipe which conveys the purified gas to its place of destination. It serves to ascertain the purity of the gas, after it has been acted on by quick-lime, by suffering the gas to pass from the tube into a solution of super acetate of lead, which speedily becomes discoloured, if the gas contains sulphuretted hydrogen. The presence of carbonic acid is rendered obvious, by a white precipitate being produced when the gas is made to pass through barytic water. The precipitate, which is carbonate of barytes, effervesces with acids.
It must be obvious that the apparatus which we have now been describing does not require to be placed in the immediate vicinity of the gas light machinery. It may be arranged in the counting-house of the overseer, who, by mere inspection, can then at all times detect the slightest irregularity or insufficiency in the process thus given to the gas light manufacture, a degree of scientific controul of which few arts can boast.
The following method has been found economical and convenient, for preserving quick-lime in a ready state, fit for the purification of coal gas.
Take the lime as soon as possible after it is burnt; put it into a pit eight or ten feet long, five or six wide, and five or six deep, constructed of brick-work and level with the ground. By this pit set a wooden trough about six feet long, three feet broad, and two feet deep. The trough should have at one end a hole about six inches square, covered with an iron grating, the bars of which are a quarter of an inch distant. Let this grating be provided with a slider, which can occasionally be drawn up to uncover, or pushed down to cover, the grating. Put three or four bushels of lime at a time into the trough; throw water on it, and mix it up into a thick fluid mass with a hoe perforated with holes. When there is a good quantity of liquid, draw up the slider and let the slacked lime run into the pit. Throw more water on the remaining unslacked lime, and lastly reject those pieces which will not slack. The trough should have a small inclination and project over the pit.
After the lime thus slacked has been five or six hours in the pit, it will take the consistence of a stiff paste, which it retains for years. It should then be kept covered to keep it clean and to exclude the free contact of the air. For those who use larger quantities of lime, several pits should be constructed in preference to one larger reservoir. When the lime is wanted for use it may be dug out with a spade, and readily diluted with a sufficient quantity of water.
The quick-lime thus prepared forms a perfect homogeneous mixture. The practice of throwing lime simply slackened into the lime cistern is a wasteful and slovenly process, as will becomes obvious on examining the waste hydrosulphuret of lime discharged from the machine, which will be found to abound with lime in a concrete form, unacted on by the substances with which it was intended to combine.
The name of gas holder, or, as it is improperly called, gasometer, is given to the vessel employed for collecting the gas and storing it up for use. In the principle and construction of this part of the gas light machinery, peculiarly valuable improvements have of late been made. They have contributed to lessen the expence of the apparatus so much, that a reservoir for storing up any quantity of gas, may now be furnished for nearly one half the sum which such a vessel cost as originally constructed.
In the infancy of the art of lighting with coal gas, the reservoir was encumbered with a heavy appendage of chains, wheel-work and balance weights, and from the construction of the machine, it was necessary to guard it from the impulse of the wind, the action of which on the gas holder, would have rendered the lights which the machine supplied with gas, unsteady.
Hence it was necessary to inclose the gas holder in a building, called the gasometer house, which formed one of the largest items of expenditure which the proprietor of a gas light establishment was called upon to defray.
Now, however, the whole of these expensive appendages is dispensed with, nor is the gasometer house to contain the gas holder any longer necessary, and the machine as now constructed may be fixed in the open air.
The gas holder, of the original construction, consists of two principal parts; first, of a cistern or reservoir of water, usually constructed of masonry, or of cast-iron plates, bolted and screwed together; and secondly, of an air-tight vessel which is closed at top and open at bottom, inverted with its open end downwards into the cistern of water. This vessel is always made of sheet-iron plates rivetted together air-tight, and was suspended by a chain or chains, passing over wheels, supported by a frame work.
If the common air be allowed to escape from the inner vessel, when its open end is under the edge of the water in the outer cistern, it will freely descend, and water will occupy the place of the air; but if the avenue of the escape be stopped, and air be made to pass through the water, the suspended inverted vessel will rise to make room for the air. And, again, if the suspended vessel be counterpoised by a weight, so as to allow it to be a little heavier than the quantity of water which it displaces, it will descend, if, the entering gas be withdrawn through an outlet made in the vessel to permit the gas to escape. But if the outlet be stopped, and air again be admitted under the vessel, it will rise again. The apparatus, therefore, is not only a reservoir for storing up the gas introduced into it, but serves to expel the gas which it contains, when required, into the pipes and mains connected with this machine.
According to this construction of the apparatus the interior inverted vessel forms strictly what is termed the gas holder. It is suspended as already stated in the outer cistern, by a chain or chains, passing over pullies, supported by blocks and frame work, and to the chain there is affixed a counterpoise balance, of such a relative weight, as to allow the gas holder a slow descent into the water, in order to propel the gas into the mains or vessel destined to receive it, with a very small and uniform weight.
It will be obvious, that when a gas holder of this construction becomes immersed in the water, it loses as much of its weight as is equal to the bulk of water which it displaces, and hence to render its descent uniform, and to preserve the gas within, of an invariable density, at any degree of immersion, a greater counterpoise is required as the gas holder rises out of the water.
Among various methods which have been adopted to attain this object, the ends of the chains by which the gas holder is suspended, have been fastened in separate grooves, in the edge of a large wheel or pulley, of such a diameter, that the gas holder rises to its full height, before the wheel makes one revolution.
In another groove in the edge of the same wheel, was fixed the end of another chain, to which a balance weight was suspended. This weight was made nearly equal to the weight of the gas holder. To equalize the density of the gas within the gas holder, at any degree of immersion of the vessel, the weight chain was made to pass over a wheel, furnished with a spiral groove, so as to make the radii of the wheel, change reciprocally with the relative weight of the gas holder, and consequently to render the pressure of the gas holder constant and uniform.
Another and more elegant method of obtaining an uniform elasticity of the gas within the gas holder, and which has been more generally adopted, consists in passing the chain or chains by which the gas holder is suspended over a pully or wheels, and making the weight of that portion of the chain, which is equal to the depth of the gas holder, or that part of it which becomes immersed into the water, equal to one half of the weight of the specific gravity of the gas holder.
It is obvious that before the purified gas can be admitted into the gas holder, the vessel must be allowed to descend to the bottom of the exterior cistern, in order to get rid of the common air which it contains. This may be effected rapidly by opening the man hole at the top of the gas holder, to cause the vessel to descend completely into the outer cistern filled with water. The man hole is then screwed up again air-tight, and the machine is ready to receive the gas. It is obvious that the operation of opening the man hole for letting out the common air, requires only to be done once prior to the commencing of the working of the apparatus.
It must be obvious that the gas holder, of which a description has been given in the preceding page, requires a machinery at once ponderous and very delicate, qualities not easily reconciled in the construction of such a machine. It is necessary that the specific gravity apparatus, or regulating chain, wheel work and balance weight, should be constructed so correctly as never to suffer the gas within the vessel, to alter its elasticity. The machinery requires an expensive framing for its support, and independently of this, the gas holder must be inclosed in a building, in order to protect it from the impulse of the wind, the action of which would render the lights supplied from the apparatus unsteady, as already stated. The expensive and cumbersome specific gravity apparatus has been wholly superseded by an ingenious contrivance called the regulator or governor. The action of this machine, for which we are indebted to Mr. Clegg, is, that it regulates the density of the gas prior to its entering into the mains, to any required degree, whatever its density may be in the gas holder.
To accomplish this object, the apparatus through which the gas passes into the mains, is provided with an aperture which is capable of being enlarged or diminished by a very slight force. To effect this object the gas is made to enter a small vessel, and then to pass through a regulating aperture, the capacity of which becomes enlarged or diminished by the velocity of the gas to a certain standard. If the pressure of the gas in the gas holder becomes increased, the regulating aperture through which the gas passes into the mains, becomes diminished, in such a proportion, that the velocity with which the gas issues into the mains, remains constant and uniform. And on the other hand, if the pressure of the gas in the gas holder becomes diminished, the regulating aperture of the governor becomes enlarged to effect the intended regulation.
The following is a concise description of the manner in which this instrument is constructed.
A, B, C, D, fig. 9, pl. III. is a hollow cylindrical vessel, or the outer case of the machine. It is made of sheet iron or copper, japanned within and without, closed at the top and bottom. It is placed between the gas holder and the mains, into which the gas is to be conveyed. a, x, is a pipe which proceeds from the outer vessel and branches upwards in the centre of the base of the outer vessel A, B, C, D. It brings the purified gas into the governor. b, T, is the outlet pipe which conveys the gas from the governor into the mains. It is placed above the inlet pipe and communicates with the interior vessel. G, H, a short projecting hollow cylinder, which proceeds downwards from the centre of the base of the outer case of the machine A, B, C, D. u, x, y, z, is the regulator, properly so called; it consists of a small conical vessel, also made of sheet iron or copper, closed at the top and open at bottom, japanned within and without. This vessel rises and falls vertically in the outer cylindrical case. A, B, C, D, of the machine, when the latter is filled with water. It is kept steady in its motion by two slender guide rods, as shewn in the sketch.
Between the inlet pipe which conveys the gas into the governor, and the outlet pipe which conveys the gas into the mains, is fixed horizontally a partition plate, having a circular aperture in the centre. This plate is seen between the letters x, T.
Through this orifice passes a perpendicular axis P, which is fixed at the top in the centre of the regulator or interior floating vessel u, x, y, z.
The interior extremity of the axis P, is furnished with a cone, having its base downwards, and projecting beyond the pipe a, x, into the short cylinder G, H. The base of this cone slightly exceeds the diameter of the orifice x, T, so as to close up entirely, when the regulator is raised to its greatest height in the outer vessel A, B, C, D. But when the floating vessel u, x, y, z, descends in the outer vessel A, B, C, the vertex of the adjusting cone P, is just entering the aperture.
The regulator is conical, and its form is in exact proportion to the loss of the weight of water which it displaces; so that the gas conveyed into it always retains an invariable density at whatever height the regulator may be immersed in the water in the outer vessel. If the outer vessel be filled with water up to the top of the central branch pipe, the interior vessel will float, and the water will stand in the outer vessel at the same height as in the inside of the regulator; hence the density of the gas within will be the same as the outer air. But the density of the gas in the regulator may be increased at pleasure by applying a weight to the top of the regulator, the water will then stand higher on the outside of the regulator than within, and this adjustment will remain uniform, because the quantity of matter of the regulator is in the ratio of its specific gravity or loss of weight as it becomes immersed in the water.
Let us suppose that the pipe above the partition plate be connected with a main, and that the outlet pipe below the partition plate be connected with a gas holder supplying gas into the machine; it will be evident that if the density of the gas in the inlet pipe becomes by any means increased, a greater quantity of gas must pass betwixt the sides of the adjusting cone and the aperture in the partition plate, the consequence of which will be that the floating regulator will rise, and therefore contract the area of the partition plate. And if, on the contrary, the gas in the inlet pipe decreases in density the regulator will descend, so that whatever density the gas may at any time assume in the gas holders or mains, its density in the floating vessel u, x, y, z, will remain uniform, and consequently the velocity of the gas passing into the mains will be regular.
For when the aperture of the partition plate would admit more gas than what is necessary for the density of the gas in the mains, the floating regulator rises, and by that means raises the adjusting cone to diminish the aperture in the partition plate, and when, on the contrary, the aperture does not allow a sufficient quantity of gas to come from the gas holders, the gas passes out of the regulator into the mains, and in so doing the regulator descends, and consequently the adjusting cone increases the opening to admit the requisite gas into the mains.
The further application of this machine, for regulating the height of the gas flames issuing from burners or lamps of different kinds will be shewn hereafter.
Fig. 7, plate VI., exhibits a perpendicular section of the gas holder at Chester. A, A, are wooden beams or pillars fixed into sockets or shafts constructed on the outside of the brick-work, and descending as seen in the design to the depth of the tank. There are four of these pillars, three only are seen in the section. B, B, are round iron guide rods rendered steady by stays at the upper extremity of the rods.
To the upper and lower edges of the gas holder are fastened eye bolts, C, C, through which the guide rods, B, B, are inserted, so that the gas holder must move steadily and firmly. D, E, are the inlet and outlet pipes which convey the gas into and out of the gas holder.
F, F, are diagonal stays for supporting the roof of the gas holder, which has a slope of ten feet from the centre to the circumference. G, is the wooden curb at the lower margin of the machine.
This gas holder is circular. It measures forty-eight feet in diameter, and thirteen feet in height; its weight is eight tons.
The regulator adapted to this gas holder, measures three feet across its base, and its height is three feet three inches. The base of the regulating cone is four inches, and its length two feet. The machine is made of sheet iron japanned within and without.
The construction of this gas holder, as exhibited plate V., fig. 2, shows a perpendicular section, and fig. 3, a plan of the machine; a, a, a, a, fig. 3, are upright pillars, two of which B, B, are seen in the section, fig. 2.
In the centre of the gas holder is fixed a pipe, which allows the gas holder to slide on the central guide rod G, made fast at the bottom of the cistern, and at the top of the cross framing. C, C, are diagonal stays; D, the inlet pipe which conveys the gas into the gas holder E; the outlet pipe F, the wooden curb.
The capacity of this gas holder is 30,000 cubic feet; its regulator is precisely similar to that before described. The weight of the gas holder, exclusive of the wooden curbs at top and bottom, is between eight and nine tons.[39]
[39] The gas holder without specific gravity apparatus, at the Bristol Gas Works, is constructed on a similar principle. Its capacity is 43,000 cubic feet. Its regulator is like those already described.
The gas holder thus disencumbered of its specific gravity apparatus, requires no building to enclose it, it may be erected in the open air, for the machine cannot suffer from the rain or snow falling upon it, nor can the action of the wind render the lights unsteady.
The saving which has been effected by these improvements is very great. A gas holder without balance weight and specific gravity apparatus, with its governor, may be erected complete for action, for little more than half the cost that would be required for the erection of an apparatus of the same capacity constructed on the old plan.
The cheapest house constructed of sheet iron to surround a circular gas holder of 15,000 cubic feet capacity, supposing the surface of its cistern or tank to be level with the ground, costs no less than £. 320. The balance weights and chains £. 60, and the cast-iron framing for supporting the specific gravity machinery £. 150.
The cost of a gas holder of the before-mentioned capacity, will be £. 300, and a cast-iron tank for it, £. 800.—If the tank be constructed of brick-work, it will cost about £. 500, and if of wood (an iron-bound vat,) it will cost £. 600.
A governor or regulating guage adapted to a gas holder of from 10,000 to 40,000 cubic feet capacity, costs £. 50. In the construction of the gas holders, as hitherto described, it is always advisable when the situation will admit it, that the diameter to the height of the machine should be in the proportion as three to two. If these dimensions be observed, and the gas holder is not burdened by iron stays, it will not displace a column of water more than one inch and a half in height. And by adapting to the machine, a governor or regulating guage, a considerable saving will be effected. The gas holder may then be constructed as shown fig. 7, plate VI., or fig. 2, plate V. A circular gas holder of 30,000 cubic feet capacity, if properly constructed, weighs no more than eight or nine tons, including its wooden curb at its lowest extremity, and its diagonal stays.[40]
[40] Mr. Lee of Manchester supplies his house, two miles distance from the manufactory, by means of a portable gas holder.[41] A small carriage upon springs conveys two square close gas holders made of wrought iron plates, and each containing fifty cubic feet of perfectly purified gas, equivalent together to about six pounds of tallow. Each gas holder weighs about 160 pounds; and has a valve at the bottom, which is opened by the upright main pipe, the moment the gas holder is immersed in the pit. The strength of one man is found sufficient for the labour of removing the gas holder from the carriage to its place.
[41] Henry’s Experiments on the Gas from Coal, in the Memoirs of the Manchester Literary and Philosophical Society, 1819.
The roof of the machine ought to be constructed of thicker sheet iron than those forming its sides. The only object of the balance weight, is to counterpoise the weight of the chain of the gas holder of the old construction, so that when the gas holder is wholly immersed in the cistern, the chain and balance weight are in equilibrium, deducting the required pressure with which the gas holder is intended to act. And this ought never to exceed from half an inch to an inch perpendicular head of water.
The sheet iron best adapted for constructing gas holders, is that known in commerce as No. 16, wire guage.[42] Gas holders made of plates of iron of this kind, have now been in use for upwards of nine years, and are not in the least injured or decayed. Self-interested views may sometimes lead unprincipled workmen to make use of sheet iron plates of a much greater thickness, but experience has sufficiently shown that any greater thickness than what has been specified is wholly unnecessary, and only serves as a drawback to the facility of the general operation.
[42] A superficial foot weighs three pounds.
The revolving gas holder is an ingenious contrivance invented by Mr. Clegg, for storing large quantities of gas. A gas holder of this construction may be erected with advantage in situations where the nature of the ground will not admit of a deep cistern either above or below the ground being constructed, without an enormous expence.
The base which it occupies is no larger than what would be required for a gas holder of equal capacity, built on the plan of the gas holders of which descriptions have been just given.
It regulates its own specific gravity. And though more expensive in the construction, yet as it does not require a deep cistern, like the machines already described, it can be erected at the same cost. The revolving gas holder is exhibited, fig. 8, plate VI. Its capacity is 15,000 cubic feet; it weighs 12 tons. Plate I., (on the title page,) exhibits a perpendicular section of the gas holder.
On inspecting fig. 8, plate VI., it will be seen that this machine is the segment of a hollow cylinder, or broad wheel, formed by two concentric cylindric surfaces of 250° each, revolving upon an horizontal axis, and supported upon a wooden frame or truss, in a brick cistern, I, K, L.
The extremity C, D, fig. 8, plate VI., or C, plate I., of the segment of the cylinder, is open, and the other extremity A, is closed. E, is a balance pipe, which connects the closed with the open extremity of the machine.
This pipe is made of such a weight as to counterpoise the interval between the open and closed end of the gas holder, so that the machine may move in a segment of a circle equally, in whatever position it may happen to be placed, and hence the gas will be discharged from the gas holder with an uniform velocity.
The balance pipe E, is closed at the part where the letter E is placed; H, is a straight pipe, which forms the communication between the balance pipe E, and the horizontal axis upon which the machine moves. This axis is hollow: it is supported by stays and braces, as shown in the design on the title page. The cistern in which the gas holder moves is 71⁄2 feet deep. It must be evident that the gas being conveyed into the open end of the hollow axis, it will pass through the pipe H, into the balance pipe E, and this being stopped up near E, the gas will proceed into the closed end of the gas holder. The operation will therefore be as follows:
Let us suppose the closed extremity of the machine to be at the surface of the water in the cistern, and the gas flowing through the axis as described, the extremity of the machine will begin to fill, and consequently to ascend; the gas holder will therefore continue to move upon its axis until the open end C, D, fig. 8, plate VI., or C, plate I., comes nearly to the surface of the water, and when the gas is required to be discharged, it will return through the same channel by which it entered. A sufficient pressure is given to this gas holder for discharging the gas at the velocity required, by means of a weight suspended to one extremity of a chain, passing over a pulley, whilst the other end is fastened into the groove of a small circle attached to the stays of the machine, as shown in the designs. The circle is graduated to express the capacity of the machine. Thus any degree of pressure may be given to the gas, and the gas holder will retrograde in an arc describing 270° of a circle, as the gas becomes discharged, until the end A, again arrives at the surface of the water.
The small curved pipe T, plate I., serves to let the common air escape out of the angular extremity of the machine, whilst filling with gas, when the margin of this part of the machine becomes immersed in the water, and to let the common air enter again, when the gas holder is discharging its contents.
S, plate I., is a friction sector, upon which the axis of the machine revolves. The advantage of this contrivance is, that the friction is very much diminished. The length of the friction sector is eight feet, the diameter of the gudgeon or axis four inches; therefore the space described by its outer circumference and its centre is in the proportion of 96 to 4.
To find the capacity of a revolving gas holder, of given dimensions, take the area of the whole diameter, then the area of the inner cylinder, multiply the difference by the length, and from this deduct one-fourth.
The collapsing gas holder is a still farther improvement by Mr. Clegg, on this part of the gas light apparatus, and certainly of all the contrivances which have been invented for collecting and storing up large quantities of gas, this machine must be pronounced to be by far the most simple, economical, and efficient. The striking advantage of the revolving gas holder which we have just been describing is, that it enables the dimensions of the tank to be very much diminished, where the nature of the ground will not admit of a cistern of great depth being sunk, except at an extraordinary expence; but the still superior feature of the collapsing gas holder which we now come to describe, is, that it may be constructed of any required capacity, and adapted to a tank or cistern of such diminished depth, as scarcely to deserve that name. It requires a sheet of water no more than 18 inches in height, so that it may be constructed in or upon ground of all descriptions, not only with every possible facility, but at an immense saving of expence.
Fig. 1, plate VII., exhibits a perspective view of this gas holder. It is composed of[43] two quadrangular side plates joined to two end plates, meeting together at top in a ridge, like the roof of a house. The side and end plates are united together by air tight hinges, and the joints are covered with leather, to allow the side plates to fold together and to open in the manner of a portfolio. The bottom edges of the gas holder are immersed in a shallow cistern of water, to confine the gas. By the opening out or closing up of the sides and ends of the gas holder, its internal capacity is enlarged or diminished, and this variation of capacity is effected without a deep tank of water to immerse the whole gas holder in, as required in the ordinary construction of rising and falling gas holders. The collapsing gas holder requires therefore only a very shallow trough of water to immerse the bottom edges of the gas holder to prevent the escape of the gas introduced into it. The lower edges of the gas holder which dip in water are made to move in an horizontal plane or nearly so, when they are opened, so that they dip very little deeper in the water when shut or folded together, than when opened out.