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mouth-pieces N, O, may be easy of access, and tition plate will press the gas against the surface one above another: the lower branch L,M, may be of the water, and cause it to pass through the placed almost horizontally, and the upper should hydraulic opening, in an equal quantity to that form with it an angle of about ten degrees. The which is introduced into the exterior chamber. retort being made red hot, the tar will be decom- This alternate filling, and discharging, of the posed, and the gas, and some other products, will contents of each chamber, will take place once How from the end M, by the pipe P, into the during every revolution of the wheel, and hence vessel Q, in which is a partition plate R, the number of times each particular chamber fig. 11, extending about half way down, and has been filled and emptied of gas may be allowing the heavy products to accumulate for a known. In fact this machine performs the office convenient time before they can interfere with of three revolving gas-holders, fixed on an horithe passage of the gas, which passes to the puri- zontal axis, and moving in a cistern, which is fiers, as usual, by the pipe s,s, fig. 12, is the outer case of the machine. One gas-holder, a moveable lid for cleansing the vessel. It is or one compartment of the machine, is always not thought necessary particularly to describe the in the act of becoming filled with gas, another construction of the furnace, which may be varied is emptying its contents into the outer case, from according as circumstances require.

which it passes into the reservoir, where it is to We may now describe the gas-metre erected be stored up, or to the lamps, where it is to be by Mr. Accum at the works in the royal mint. burned, and the third compartment is stationary, Ii consists of a hollow wheel or cylinder, made or in an equilibrium. The wheel in any situaof thin iron plate; revolving upon an horizontal tion will therefore always have one of its receivaxis, in the manner of a grind-stone; this wheeling, and one of its discharging valves open, and is enclosed in a cast iron air-tight cask contain- consequently it will revolve. ing water.

Now to ascertain the quantity of gas disThe cylinder, or wheel, is composed of two charged by one revolution of the wheel, we need circular channels, 1 and 2, fig. 1 plate II. con- only to know the capacity of the chambers, and centric to each other. The larger or outer chan- add them together. Let us for example suppose, nel, 1, is divided into three equal compartments, that each chamber contains 576 cubic inches, by partition plates, marked a, as shown in the then one revolution of the wheel discharges a design. The compartments are provided with cubic foot of gas. To register the total number hydraulic ducts or valves, made at the upper of revolutions which the wheel makes in a cerpart of every partition plate a, a, a, and by means tain time, a train of wheel-work is conof them a communication is formed between the nected with the axis of the metre; it consists of larger concentric channel, 1, and the outer case a pinion impelling a common train of wheelin which the wheel revolves. Similar valves are work, composed of any number of wheels. The also placed at the foot of each partition plate, pinion on the axis of one wheel, acts into the they are seen near the letters a, a, a, and by this circumference of the next wheel, and, the circummeans a communication is established, between ference of the wheel being as ten to one, it is each compartment or chamber of the larger con- obvious while the metre makes 1,000,000 revocentric channel, 1, and the smaller interior circle, lutions, if the series consist of six wheels, the 2, of the wheel.

last wheel of the series will only have made On inspecting the design, it will be seen that one revolution. Each axis of the wheels is the valves are situated in opposite directions to provided with a finger and dial-plate, divided each other ; hence there can be no communication into ten parts; therefore any number of revopither between the inner smaller concentric chan- lutions may be read off at any time by inspection nel 2, and the larger compartment of the wheel betwixt 10,000,000 and one. The velocity with 1, nor between the latter compartment, and the which the metre acts, is of course in proportion exterior case, in which the wheel revolves, ex to the quantity of gas passing through it. Thus cept through the valves a, a, a, which form the suppose there is a burner or gas-lamp connected communicating ducts. It will be seen also, that with the machine, of one foot capacity, lighted, these valves are carried from one chamber of which consumes four cubic feet of gas in an the machine into another, but in opposite direc- hour, the gas metre performs four revolutions tions; the entry into one chamber being in the per hour, and so on for every number of burnopposite direction to the hydraulic duct, placed ers or lamps, not exceeding the number which in the other chamber. From these particulars the machine is calculated to supply. the action of the machine will be obvious. The gas-holder, of the original construction,

Let us suppose that the outer case, in which consists of two principal parts ; first, of a cistern the wheel revolves, be filled with water to about or reservoir of water, usually constructed of an inch above the axis of the wheel, and that masonry, or of cast-iron plates, bolted and gas is conveyed into the interior small channel, screwed together; and secondly, of an air-tight by a pipe, passing along the axis, so as to allow vessel which is closed at top and open at botthe wheel to turn freely round, and that the pipe tom, inverted with its open end downwards into is turned up at right angles in the inner cham- the cistern of water. This vessel is always made ber, and projects a little way above the sur- of sheet-iron plates riveted together air-tight, face of the water, as shown in the design, and was suspended by a chain or chains, passing The gas then must enter into the interior cham over wheels, supported by a frame work. If ber of the wheel above the surface of the water, the common air be allowed to escape from the and must press against the adjacent partition; inner vessel, when its open end is under the edge it will therefore cause the wheel to turn round, of the water in the outer cistern, it will freely and, in consequence of this motion, the next par- descend, and water will occupy the place of the

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air; but if the avenue of the escape be stopped, top of the gas-holder, to cause the vessei to deand air be made to pass through the water, the scend completely into the outer cistern filled suspended inverted vessel will rise to make room with water. The man-hole is then screwed up for the air. And, again, if the suspended vessel again air-tight, and the machine is ready to rebe counterpoised by a weight, so as to allow it ceive the gas. It is obvious that the operation to be a litle heavier than the quantity of water of opening the man-hole, for letting out the comwhich it displaces, it will descend, if the enter mon air, requires only to be done once prior ing gas be withdrawn through an outlet made in to the commencing of the working of the appathe vessel to permit the gas to escape. But if ratus. the outlet be stopped, and air again be admitted The collapsing gas-holder was contrived by under the vessel, it will rise again. The Mr. Clegg, and certainly, of all the contrivances apparatus, therefore, is not only a reser- which have been invented for collecting and voir for storing up the gas introduced into it, storing up large quantities of gas, this machine but serves to expel the gas which it contains, must be pronounced to be by far the most simwhen required, into the pipes and mains con- ple, economical, and efficient. The striking nected with this machine. According to this advantage of the revolving gas-holder is, that it construction of the apparatus, the interior in- enables the dimensions of the tank to be very verted vessel forms strictly what is termed the much diminished, where the nature of the ground gas-holder. It is suspended as already stated in will not permit of a cistern of great depth being the outer cistern, by a chain or chains, passing sunk, except at an extraordinary expense; but over pulleys, supported by blocks and frame the still superior feature of the collapsing gas work, and to the chain there is affixed a counter- holder which we now come to describe, is, that poise balance, of such a relative weight as to it may be constructed of any required capacity, allow the gas-holder a slow descent into the wa- and adapted to a tank or cistern of such diter, in order to propel the gas into the mains or minished depth, as scarcely to deserve that vessel destined to receive it, with a very small name. It requires a sheet of water no more and uniform weight.

than eighteen inches in height, so that it may be It will be obvious that, when a gas-bolder of constructed in or upon ground of all descripthis construction becomes immersed in the water, tions, not only with every possible facility, but it loses as much of its weight as is equal to the at an immense saving of expense. bulk of water which it displaces; and hence to Fig. 2, plate II. Gas Light, exhibits a perrender its descent uniform, and to preserve the spective view of this gas-holder. It is composed gas within of an invariable density, at any de- of two quadrangular side plates joined to two gree of immersion, a greater counterpoise is end plates meeting together at top in a ridge required as the gas-holder rises out of the water. like the roof of a house. The side and end Among various methods which have been adopted plates are united together by air-tight binges, to attain this object, the ends of the chains by and the joints are covered with leather, to allow which the gas-holder is suspended, have been the side plates to fold together, and to open in fastened in separate grooves, in the edge of a the manner of a portfolio. The bottom edges large wheel or pulley, of such a diameter, that of the gas-holder are immersed in a shallow the gas-bolder rises to its full height before the cistern of water, to confine the gas. By the wheel makes one revolution. In another groove, opening out or closing up of the sides and ends in the edge of the same wheel, was fixed the end of the gas-holder, its internal capacity is enof another chain, to which a balance weight was larged or diminished, and this variation of capasuspended. This weight was made nearly equal city is effected without a deep tank of water to to the weight of the gas-holder. To equalise immerse the whole gas holder in, as required in the density of the gas within the gas-holder, at the ordinary construction of rising and falling any degree of immersion of the vessel, the weight gas-holders. The collapsing gas-bolder requires chain was made to pass over a wheel, furnished therefore only a very shallow trough of water to with a spiral groove, so as to make the radii of immerse the bottom edges of the gas-holder to the wheel change reciprocally with the relative prevent the escape of the gas introduced into it. weight of the gas-holder, and consequently to The lower edges of the thin gas holder, which dip render the pressure of the gas-holder constant and in water, are made to move in an horizontal plane uniform.

or nearly so, when they are opened, so that they Another and more elegant method of obtain- dip very little deeper in the water when shut or ing a uniform elasticity of the gas within the folded together, than when opened out. gas-holder, and which has been more generally For this purpose the top or ridge joints, which adopted, consists in passing the chain or chains unite the two sides of the gas-holder, are slightly by which the gas-holder is suspended over a raised up when the sides close or approach topulley or wheels, and making the weight of that gether, or slightly depressed when the sides open portion of the chain which is equal to the depth out or recede from each other. To guide the of the gas-holder, or that part of it which be- whole gas-holder in this movement two perpencomes immersed in the water, equal to one- dicular rods rise from the bottom of the shallow half of the weight of the specific gravity of the tank which pass through sockets in the ridge gas-holder. It is obvious that, before the puri- joints at the upper part of the gas-holder. These fied gas can be admitted into the gas-holder, the sockets are secured by collars of leather round vessel must be allowed to descend to the bottom the shafts or rods, to prevent the escape of the of the exterior cistern, in order to get rid of the gas, and they are braced by chains proceeding common air which it contains. This may be from their upper extremities ard fastened at the effected rapidly by opening the man-hole at the ground on each side of the tank

The weight of the gas-holder is balanced by supported and fixed upon legs mn, gives motiot. levers bent in the form of the letter L, and placed to an axle carrying a small eccentric wheel, or in the inside of the gas-holder. These levers move crank n, in order to raise the lever o, which has on centre-pins fixed at the bottom of the shallow its fulcrum on the axle of the wheel

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and rests trough, which pass through the angles of the L upon the periphery of the eccentric wheel. The levers. The perpendicular arms of the levers lever being thus raised, a small spring catch P, are jointed at their upper extremities to the attached to it, takes into the teeth of the wheel sides of the gas-holder, nearly in the middle. 9, and, when the lever again descends, the catch At the ends of the horizontal arms of the L drives the wheel round a short way. Another levers, are weights to counterbalance the weights spring r holds the wheel as the lever again rises ; of the gas-holder, and both sides of the gas and, in this manner, by many revolutions of the holder are provided with these kinds of levers, eccentric wheel n, raising and lowering the lever which, at the same time that they balance its 0, the wheel 9 is driven entirely round. A weight, cause the ridge joint of the machine to pinion upon the axle of q works in the wheel s, rise and fall, as before described, so that the which carries the index round a dial-plate, and under edges of the gas-holder, which are im- thus registers the quantity of gas which has pass mersed in the water to confine the gas, musted uniformly through the aperture c. Should the move in an horizontal plane instead of describ- pressure of the gas, however, not be uniform, the ing an arc of a circle as they would do if the flap of the vessel b will be raised or depressed ridge joint was a fixed centre of motion. When accordingly, as indicated by the dotted line. the gas-holder is closed, the perpendicular arms When this happens, the connecting rods h, i, k, of the levers stand nearly in a perpendicular will raise or depress the lever o, so as to make it position; but when the gas-holder is opened out, move through a greater or less arch, and consethe levers become inclined. And as they move quently drive forward a greater or less number upon a fixed fulcrum at their lower extremities, of the teeth of the wheel q. Upon the arm k is and are jointed to the sides of the gas-holder at a stop t, which, when the flap of b descends and their upper extremities, they allow the whole of contracts the passage of the gas, will, by the the gas-holder to descend gradually upon the connecting arms, h, i, k, be raised so high as to guide rods nearly in the same degree as the lower prevent the lever from being acted upon by the edges would rise up if the ridge joint was stable, eccentric wheel during a part of its revolution; and if the sides described an arc of a circle. consequently, the arch described by the lever o It is obvious, however, that the latter move- will be smaller, and the progress of q and s dimiment is not very essential, but it is convenient . nished : but when the lap of the vessel b is and necessary to make a very inconsiderable raised, and enlarges the passage for the gas, then depth of water, in the trough or tank, serve the the stop t will be brought sufficiently low to purpose intended. It may be also observed, enable the lever o to be acted upon by the perithat the sides of the collapsing gas-holder may phery of the eccentric wheel during the whole be made to unfold or open on a fixed ridge point revolution: in consequence of which, the arch as a centre of motion ; but it will then require a described by the lever o will be greater, and the considerable depth of water in the tank to keep progress of the wheels q and sincreased. A nut the lower edges of the sides and ends of the v, having a right and left screw, is employed to machine always beneath the surface of the water, adjust the length of the rod k. For the purpose because the sides of the gas-holder then describe of stopping the clock movement, when the supply an arc of a circle when they are open.

of gas is stopped, a paul lever u rises with the Mr. Malam has contrived an instrument which rod k, for the purpose of locking the eccentric serves to exhibit upon a dial-plate the quantity wheel. In order to stop the passage of gas when of gas which passes through a tube in its progress the clock movement requires winding up, a to the burners. It is represented in fig. 3 plate pinion upon the axis of the fusee works in the II., where a is the pipe through which the gas dotted toothed arch w, w. The operation of passes that is to be measured; b an air-tight winding up, carries the rack back; but, as the vessel, like bellows, with the upper flap rising movement goes down, the rack advances, by or falling upon a joint or hinge, and constructed which a tooth x, upon its axle, presses upon the of leather or cloth, protected against the chemi- short end of the lever y, which it raises, and cal action of the gas.

From this vessel the gas causes to lift the rod k: at the same time making escapes through the aperture c, into the outer the rod h press down the flap of b, in order case dd, and hence through the exit-pipe e, to to bring the aperture c in contact with the plate the burners. The aperture c, is partially en- f, and thus obstruct completely the passage of the closed by the flat plate f suspended or swinging gas. upon the rod g, and accommodating itself to the Messrs. J. and P. Taylor are the first persons descent of the flap: When equal quantities of who have resorted to oil as substance gas pass along in the direction a, f, b.c, d, e, in from which gas for illumination could be easily equal spaces of time, which is generally the case, and cheaply prepared; and, in the construction the quantity of gas will be indicated by the clock of a convenient apparatus for the decomposition movement shown in the upper part of the figure, of this body, they have fully shown its numerous provided the clock always stops with the supply advantages over coal, while they have afforded of gas, and goes again when the supply com- the means of producing the most pure and brilmences; for effecting which, there is a particular liant flame from the inferior and cheap oils, contrivance, which shall be afterwards described. which could not be used in lamps. The appaThe clock movement in the cylindrical box l, ratus for the purpose is much smaller, much

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sinpler, and yet equally effectual, with the best room required to contain the gas is directly dicoal-gas apparatus. The retort is a bent cast-iron minished, the object is so far obtained ; and tube, which is heated red by a small convenient when that takes place to one-half, or even onefurnace, and into which oil is allowed to drop by third, it is of very great importance. It in a a very ingenious apparatus ; the oil is immedi- great number of cases brings the size of the appaately volatilised, and the vapor in traversing ratus within what can be allowed in private the tube becomes perfectly decomposed. A houses; and, in consequence of the rapidity with mixture of inflammable gases, which contains a which the retort can be worked, the gasometer great portion of olefiant gas, passes off; it is may again be reduced to a still smaller size. washed by being passed through a vessel of Another advantage gained by the small quantity water (which dissolves a little sebacic acid, and of gas required for a flame is the proportionate which seldom requires changing), and is then diminution of heat arising from the lights. The conducted into the gasometer.

quantities of heat and light produced by the The facility and cleanliness with which gas is combustion of inflammable gases are by no means prepared from oil, in the above manner, may be in the same constant relation to each other: one conceived from the description of the process. frequently increases, whilst the other diminishes, A small furnace is lighted, and a sufficient quan- and this is eminently the case when coal gas and tity of the commonest oil is put into a small iron oil gas are burned against each other. The vessel, a cock is turned, and the gas after pass- quantity of heat liberated is, speaking generally, ing through water in the washing vessel goes as the quantity of gas consumed, and this is into the gasometer. The operation may be stop- greatest with the coal gas; but the quantity of ped by shutting off the oil, or, to a certain ex- light is nearly as the quantity of carbon that is tent, hastened by letting it on more freely; the well burnt in the flame; and this is greatest in small quantity of charcoal deposited in the retort the oil gas. is drawn out by a small rake, and the water of The very compact state in which the apparatus the washer is very rarely changed.

necessary for the decomposition of oil can be The gas prepared from oil is very superior in placed, the slight degree of attention required, its quality to that from coal ; it cannot possibly certainty of action, its cleanliness, and the nucontain sulphureted hydrogen, or any extraneous merous applications of which it admits, in the substance; it gives a much brighter and denser use of its furnace for other convenient or fame; and it is also more effectual, viz. a economical purposes, render it not only unobsmaller quantity will supply the burner with jectionable, but useful in manufactories and fuel. These peculiarities are occasioned, in the establishments; and these favorable circumfirst place, by the absence of sulphur from oil, stances are accompanied, not by an inferiority in and then by the gas containing more carbon in the flame, or increased expense, but by an imsolution. As the proportion of light given out proved state of the first, and saving in the latter. by the flame of a gaseous compound of carbon Messrs. Taylors have shown great ingenuity and hydrogen is, in common circumstances, in in the construction of their whole apparatus, but proportion to the quantity of carbon present, it the washer and gasometer deserve particular is evident that the gas which contains a greater notice for their remarkable simplicity also. In proportion of olefiant gas, or supercarbureted hy- the washer, two planes are fixed in a box or drogen than coal gas, will yield a better and cistern, in a direction not quite horizontal, but brighter light on combustion. It is necessary, inclined a little in opposite directions; the planes in consequence of the abundance of charcoal in are traversed nearly across by slips of wood or solution, to supply the gas when burning with metal, fixed in an inclined position on the under plenty of atmospheric air; for as there is more surface, and which alternately touch one side of combustible matter in a certain volume of it the cistern, leaving the other open and free. than in an equal volume of coal gas, it of neces. These planes being immersed in water, the gas sity, must have more oxygen for its consumption. is thrown in under the lowest ridge; and, by its The consequence is, that less gas must be burnt ascending power, is made to traverse backward in a flame of equal size, which will still possess and forward along the ridges fixed on the planes, superior brilliancy; that less is necessary for the until it escapes at the highest part of the uppersame purpose of illumination; and that less heat most ridge. Thus, with a pressure of five or will be occasioned. From five and a half to six six inches of water only, it is made to pass cubical feet of coal gas are required to supply an through a distance of fourteen or sixteen feet Argand burner for an hour; two cubical feet to under the surface of the fluid, and become well two and a half of that from oil, are abundantly washed. The smaller gasometers are made of sufficient for the same purpose. One important thin plate iron, and, being placed in a frame of advantage gained by the circumstance, that so light iron work, look more like ornamental stoves small a quantity of this gas is necessary for than the bulky appendages to gas apparatus, burners, is, that the gasometer required may be which they supply. The larger ones are made small in proportion. The gasometer is the most very light, and, when in pieces, very portable, bulky part of a gas apparatus, and that least ca- by being constructed of a frame of wood work, pable of concentration; and wherever it is placed, in the edges of which are deep narrow grooves; it occupies room to the exclusion of every thing plates of irou fit into these grooves, which, being else. Some very ingenious attempts have been caulked in and painted over, make a light and made to diminish its size and weight, as in the tight apparatus. These are easily put together double gasometer, and others, but without re- in any place; and may therefore be introduced markable success. Here, however, where the into a small apartment, or other confined space,

where a gasometer already made up would not gas, which renders so small a volume necessary enter.

that one cubic foot of oil-gas will be found to The general advantages of oil-gas, when con go as far as four of coal-gas. This circumstance trasted with coal-gas, are as follows :The ma- is of great importance, as it reduces in the same terial from which it is produced, containing no proportion the size of the gasometers which sulphur, or other matter, by which the gas is are necessary to contain it; this is not only a contaminated, there are no objections to its use, great saving of expense in the construction, but on account of the suffocating smell, in close is a material convenience where room is limited. rooms. It does no sort of injury to furniture, The calculations on the cost of light from oilbooks, plate, pictures, paint, &c. All the costly gas are taken on the usual price of good whaleand offensive operation of purifying the gas by oil; but, it is to be observed, that cheaper oils lime, &c., is totally avoided when it is obtained will answer the purpose nearly as well, and many from oil. Nothing is contained in oil-gas which of these are often to be procured; and the can possibly injure the metal of which the con- whole expense may be materially lessened by veyance pipes are made. The oil-gas, contain- their use. ing no unmixed hydrogen, which occasions the In the course of their first experiments, great heat of coal-gas, there is no greater heat Messrs. John and Philip Taylor were surprised in proportion from the flame of oil-gas than to find that the apparatus they employed grafrom burning oil in lamps, wax-candles, &c. dually lost its power of decomposing oil, and

The apparatus for the production of oil-gas is generating gas. On investigation, they discomuch less expensive than that necessary to make vered that the metallic retorts, which had origicoal.gas; it occupies much less space; it re- nally decomposed oil and produced gas in quires much less labor and skill to manage it; abundance, ceased in a very great degree to posit is not so liable to wear and tear, and not so sess this power, although no visible change bad costly to repair as a coal-gas apparatus; there taken place in them. The most perfect cleaning are no offensive products to remove; and, on its of the interior of the retort did not restore the present improved construction, it may be intro- effect, and some alteration appears to be produced into any dwelling-house without nuisance. duced on the iron by the action of the oil, at a The economy of light from oil-gas may be judged high temperature. of from the following data :-One gallon of com Fortunately the experiments on this subject mon whale-oil will produce about ninety cubic led to a most favorable result, for it was found feet of gas, and an Argand burner will require a that, by introducing fragments of brick into the cubic foot and a half per hour to maintain a per- retort, a great increase of the decomposing power fect light; consequently, a gallon of oil, made was obtained, and the apparatus has been much into gas, will afford such a light for sixty hours, improved by a circumstance, which, at one and the expense, at a moderate price of oil, will time, appeared to threaten its success. A small be, allowing for coals, labor, &c., not more for portion of the oil introduced into the retort, still one burner than three farthings per hour. passed off undecomposed; and, being changed

Such a burner will be equal in intensity of into a volatile oil, it carried with it a great porlight to two Argand oil-lamps, or to ten mould tion of caloric, which rendered the construction candles. The expense of Argand oil-lamps is of the apparatus more difficult than was at first usually admitted to be about 14d. per hour each. anticipated ; but, by the present arrangement of Supposing ten mould candles to be burning, at its parts, this difficulty is fully provided for, and four to the 1b., will be 2} lbs., costing 2s. 11d., the volatilised oil is made to return into the oilone-tenth part will be consumed in each hour, receiver, whence it again passes into the retort; and the cost of the light is then 3 d. per hour. so that a total conversion of the whole into If wax-candles be employed, the expense of a gas is accomplished without trouble, or the quantity of light equal to a gas-burner, for one escape of any unpleasant smell. hour, by the same mode of reckoning allowing The only residuum in the retort is a small a candle to burn ten hours, and taking the price quantity of carbon, and the only products beof wax-candles at 4s. 6d. per 1b., will cost about sides the gas are a minute quantity of sebacic 14d.

and acetic acids, and a portion of water, all The account will, therefore, stand thus : which are easily separated by passing the gas

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through a vessel containing water. Argand burner, oil-gas, per hour

The superiority of the light from oil-gas over Argand lamps, spermaceti oil . 3

other artificial lights, is fully shown by its renMould-candles

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dering the delicate shades of yellow and green Wax-candles

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nearly as distinct as when viewed by solar light.

Mr. De Ville of the Strand, who has made In many cases it may be desirable to use a many important experiments and observations much smaller quantity of light, than such a on gas illumination, with a view of applying it burner, as the one above calculated upon, might to light-houses, is inclined to estimate the aveproduce; and, instead of the light of ten can- rage produce in gas of a gallon of oil, at eighty dles, that of one or more may be given, by using cubical feet. A single jet burner, giving the burners of a different description; and the ex- light of two candles and a half, consumes half a penditure of gas and the cost will be reduced in cubical foot of gas per hour. A double jet conproportion.

sumes three quarters of a foot to give twice the The 'oil-gas has a material advantage over above light, and a treble jet requires one foot. coal-gas, from its peculiar richness in olefiant The light of an Argand burner of coal-gas, com

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