When the gas has been carried through the pipe z q y, and its different ramifications, to the places where it is to be burnt, the passage terminates in a small apparatus, called a burner, perforated with one or more small holes, about one-thirtieth of an inch in diameter. The most sim ple of these terminates in a spherical surface, as seen in Fig. 9. There is one hole in the centre, and several others around it. The surrounding holes, if it were not for the upward current of air, would give flames, radiating in straight lines from the centre of the spherical burner ; but the upward motion of the heated air causes the flame to curve upwards, like the spur of a game-cock, and hence they have been technically called cackspur burners. Fig. 10. is a bracket, at the end of which is a burner, terminat ing in the face of a cylinder, near the outer edge of which is a circular series of holes, from which the flame rises per pendicularly. These are surrounded by a glass like the Argand lamp. In its general appearance it is so like this lamp, as to have acquired the name of the ilrgand burner. Figs. 11. and 12. are a plan and section of this burner upon a larger scale. The holes in the inner circle, Fig. 11. are supplied with gas front the cavity C, Fig. 12 : The same holes appear in section at a b, Fig. 12. The holes in the outer circle, Fig. 11. communicate with the cavity c f, Fig. 12. which also communicates with the atmosphere by the openings i k ; gh is an ornamented rim for the reception of the glass. The air from the glass becoming heated by the flame, rises, and at current takes place from i k, through the cavity c f, and between the burner and the glass. This current in the Argand lamp is both within and without the circular flame, and serves to supply the lamp with oxygen for burning the smoke, as well as to keep the flame steady. In the gas lights there is no smoke to burn : the current of air, therefore, is not so essential. It has the good effect, however, of keeping the flame steady, which otherwise would be agitated by the slightest motion of the surround ing air. Fig. 10. spews the manner of bringing the gas to supply a bracket-lamp fixed to the wall : The stop-cock a is connected with the pipe behind the board c d, which also communicates with the pipe b leading to the burner. Fig. 9. is provided with a similar plate to screw to the wall. These brackets are capable of moving in a horizontal direc tion. The end of the tube b is ground into the little globe 8, so that it will turn round without allowing the air to escape. Fig. 9. is similarly constructed. A great variety of these ornamental brackets, chandeliers, candelabras, &c. will be found in Mr Accum's work upon gaslights.
The apparatus above described is upon a small scale, compared with what would be required for lighting a large manufactory, or upon the scale practised for lighting the streets and shops in the metropolis. The gazometer, lime vessel, and tar vessel, are all made of cast and wrought iron, precisely in the same way that would be recommend ed upon the largest scale. It would be found impractica ble to increase the fire and the retort to the same extent to which the other apparatus may be increased. It would be improper to make a fire to heat a greater length than from six to eight feet. And if the cavity of the retort were more more than 12 inches wide, the coal would not be com pletely decomposed in the centre. It is found, therefore, more advantageous when a greater supply of gas is want ed, than would be afforded by a vessel of the above dimen sions, to use additional retorts and fires, all communica ting with the same gazometer, lime-vessel, &c. In Fig. 7.
there is but one furnace, but it may easily be supposed that a series of furnaces may join this on the left hand.
Each retort having a tube n, they may all be connected with one common pipe c, which is the condenser : to show this, the pipe c in this figure is broken off on the left hand.
When the vessel D is made very large, it requires to be first formed in a skeleton of wrought or cast iron, and af terwards covered with iron plate.
It is strongly advised, where it is practicable, that the retorts should be kept in constant action night and day for the season, or at least never allowed to go below a red heat. The first portion of oxide which forms upon the surface, when allowed to cool, cracks and falls off, leaving a new surface to be acted upon the next time it is heated. By thus being every clay heated and cooled, a retort will be destroyed in a few months. When they are kept continual ly red hot, they ft equently last three winters. The writer of this article is indebted to Mr Lee of Manchester for this fact.
In discharging the retort at a red heat, the coak may drop through an opening into a cellar below, the hole being afterwards closed ; without this contrivance, the operation would be much annoyed. In applying the gas lights to the streets and shops, pipes of cast iron are employed running along each side of the street, of different sizes, from two to four inches in diameter, according to the supply. The main streets have larger pipes, called mains, from which smaller pipes proceed, to light the cross streets, alleys, and courts. T! ‘e pipes are perforated opposite to the shop to be lighten, and an iron pipe ground air tight into the hole. With this other iron pipes are connected, to convey the gas to the place where it communicates with the burner. The pipes in the streets are laid so near the surface, as not to be disturbed by the carriages, or interfere with the pay ing. They are joined together by slipping one end of one into a widened part in the end of another. The cavity be tween the inside of one, and the outside of the other, which is nearly one inch, is filled with melted lead, which when set, is afterwards hammered in by the end of a punch.
Having generally described the apparatus used in light ing by gas, we shall give some statements respecting its economy compared with other means of lighting.
Mr Murdoch, of whom we have before spoken, has pub lished a statement of the expence of gas lighting, compared with candles, in the Philosophical Transactions of London, for the year l808. He begins by ascertaining that a tallow candle, of six in the pound, is consumed at the rate of 175 grains, or 1.4 of an ounce in one hour ; and that half a cubic foot of carburetted hydrogen, such as comes from cannel coal, burnt the same time, producing a light of the same intensity.
In the calculation of the expence of lighting by gas, he takes his estimate from the manufactory of Messrs Lee and Philips of Manchester, the apparatus being put up by him self. He employed 271 Argand burners, each being equal to four candles of the size abovementioned, and 633 cock spur burners, each being equal to 2+ candles, the whole amount being equal to 2500 candles of the same size. From what has been stated, it will appear, that to keep so many lights up, will require an hourly consumption of 1200 cubic feet of gas.