GAS LIGHTING. The art of procuring and applying to the purpose of illumination the inflammable gases evolved by animal and vegetable matter when exposed in close vessels to a high temperature. This important and highly beneficial invention originated in the researches of modern chemists; but a long period elapsed between the scientific discovery of the facts upon which the process is founded, and their successful application to practical pur poses. The fact that a permanently elastic and inflammable teriform fluid is evolved from pit coal during its destructive distillation, appears to have been first ascertained experimentally by the Rev. Dr. Clayton, whose account of his dis covery was published in the Transactions of the Royal Society, Vol. XLI., for the year 1739. Dr. Hales subsequently made experiments on pit coal, and found that, when distilled in close vessels, nearly one-third of the weight of coal passed off in inflammable vapour. Further experiments were made by Dr Watson, Bishop of Llandaff, in 1767; but no practical application appears to have been made of these discoveries for a long period. The merit of such application appears to belong to Mr. Murdock, who, in 1792, commenced a series of experiments at Redruth, in Cornwall, upon the quantity and quality of the gases contained in different substances, as coal, peat, and wood ; in the course of which experiments it occurred to him, that, by confining and con ducting the gas in tubes, it might be employed as an economical substitute for lamps and candles. The distillation was performed in iron retorts, and the gas conducted through tinned iron and copper tubes to the distance of seventy feet. At this termination, as well as at the intermediate points, the gas was set fire to as it issued through apertures of different diameters and forms, purposely varied to ascertain which would answer best ; amongst these forms were the argand burner and the cockspur burner, which are the two most generally employed at the present day. Bags of leather and of varnished silk, and vessels of tinned iron, were also filled with the gas, which was set fire to and carried from room to room, in order to ascertain its applicability as a movable light. Mr. Murdock's constant occupations prevented his pursuing the subject further until 1797, when he renewed his experiments upon coal andpeat, at Old Cum nock, in Ayrshire. In 1798 he constructed an apparatus for lighting the works of Messrs. Bolton and Watt, at Soho; and in 1802, on the occasion of the re joicings for the peace, the whole of the works were illuminated with gas. In 1803 and 1804 Mr. Winsor made public exhibitions of the general nature of gas lighting at the Lyceum Theatre, and proposed to light the public streets by means of gas ; but the extravagance of his statements respecting the advan tages of the scheme were prejudicial to the plan ; and although an experiment was made by lighting up a portion of Pall Mall, it was soon abandoned, and the practice did not come into successful operation until the year 1813, when the Chartered Gas Company erected their works at Peter-street, Westminster. Since this period the practice of gas lighting has come into general use with astonishing rapidity; important improvements have been made in the various processes connected with it, and gas is now extensively procured from numerous substances beside pit coal, such as oil, tar, resin, &c. We shall now proceed to give a general view of the subject, by describing the process of gas making as usually conducted at the Coal Gas Works.
'A number of cast-iron vessels, called retorts, generally of a cylindrical or of an oval shape, and set in a brick furnace, are heated to redness, and then about half filled with coal, and the mouths of the retorts closed and carefully luted. In a short time the decomposition of the coal commences, and the volatile parts separating from the fixed parts, are conducted by bent tubes called dip pipes, into a large horizontal cast-iron tube called the hydraulic main, from its being half full of water, into which the ends of the dip pipes are immersed, so that the gas and vapours may be forced to pass through the water, which condenses a portion of the tar and ammonia, whilst the gas ascends to the upper part of the hydraulic main ; from this it passes by a pipe to the condenser, which consists of a number of metallic pipes or compartments, surrounded by cold water. In its passage through this vessel the gas becomes so much cooled as to occasion the remaining portion of the tar and ammonia to be condensed, which latter products pass into the tar cistern, whilst the gas passes into the purifier, where it undergoes a process by which the carburetted hydrogen, which is the gas employed for illumination, is freed from the sulphuretted hydrogen, and carbonic acid evolved with it ; it then passes through the gas meter, in order that the quantity may be registered on its way to the gas holder (or gasometer, as it is improperly called), in which it is stirred up till wanted for use, being conveyed in any required direction by pipes connected with ;the gasometer. For the further elucidation of the subject, a general view of the
apparatus, with explanatory remarks, will be found on the following page. a Ft g 1. in the following engraving, represents a portion of a bench of retorts, in which five elliptical retorts b b are exhibited, set in an oven, the mouth of which is covered by the cast-iron plate c, having apertures for the introduction of the retorts, which are secured to the oven plate by flanges at their mouths, and the other extremity is supported by a cast-iron stud projecting from it and resting in a cast-iron socket at the back of the oven. This plan of setting retorts, which affords great facilities in their removal when burnt out, and in replacing them with others, was first employed at the Westminster Gas Works, and is the invention of Mr. Malam, of that establishment. The fires for heating the retorts are not seen, being situated at the back of the oven, by which arrange ment the annoyance of the heat to the men who charge the retorts from the elevated platform d, is considerably diminished; the coke, as it is raked from the retorts, falls through apertures e e in the platform, to which apertures are fitted trap doors, or movable gratings ; f f are the dip pipes, by which the gas enters the hydraulic main g, a transverse section of which, upon a larger scale, is shown in Fig. 2 ; h is the pipe by which the gas is conveyed from the hydraulic main to the condenser, to be divested of the tar and ammoniacal liquor. Various arrangements have been employed for this purpose ; that shown in the engraving, and which we believe to be generally preferred, is the invention of Mr. Perks, and consists of a close vessel k divided into compart ments 14 each communicating with the adjacent one by parallel rows of bent pipes m tn, which are surrounded by water contained in the tank n, erected upon the top of k. The gas entering the condenser by the pipe h passes succes sively through the several rows of bent pipes until it arrives at the exit pipe o, which conveys it to the purifier; by which prolonged contact with a great extent of cooling surface, the tar and ammoniacal liquor become condensed, and fall to the bottom of the compartments 14 and from them are conveyed to the tar vessel p, in which the tar, from its greater specific gravity, occupies the lower portion, and is drawn off by the lower cock, whilst the ammonia, which lies above it, is drawn off by the upper cock ; q represents the most approved con struction for a purifier when cream of lime is the material by which the car buretted hydrogen is freed from the sulphuretted hydrogen and carbonic acid, with which it is still contaminated after leaving the condenser. In this arrange ment of the purifying vessels, three cylindrical vessels r r r are placed one over another, and from the top of each descends a smaller cylinder a as, which does not reach the bottom of the larger cylinder, and which has attached to its lower end a broad flange or shelf. The larger cylinders are filled with cream of lime to about one-half their depth, which is kept in constant agitation by broad vanes 11 attached to the spindle u, passing through stuffing boxes in the several cylinders. The gas entering the lower small cylinder by the pipe o depresses the liquid therein below the shelf, and then rises up through the fluid into the upper part of the outer cylinder; from whence it is conveyed by the bent pipe v to the second interior cylinder, and from it, in a similar manner, to the third, from which it escapes, as before described, to the outer cylinder, and from thence passes by the pipe Iv to the gasholder, or gasometer z, as it is commonly termed. The gasholder consists of a large outer cylindrical cast-iron vessel or trunk y, nearly filled with water, in which is inverted another cylinder z of sheet iron, a few inches less in diameter, and open at the bottom ; the inner is usually suspended by a chain passing over pulleys, and having counterbalance weights attached to them, so as to allow the vessel to rise easily by the upward pressure of the gas upon its entering. For the purpose of suspending the inner vessel, a heavy frame, or bridge, was formerly erected over the whole ; but a much superior method is now generally employed ; in the centre of the vessel z is a tube of about three feet diameter, through which rises a cast-iron pillar 2 to a plate, on the to of which are fixed the balance wheels, the weights 3 3 rising and falling within the pillar. From the gasholder the gas is conveyed by the eduction pipe to the street mains, and from there, or from the various service pipes branching from them, it is conveyed, by small wrought pipes, to the street or private lamps. In order to regulate the flow of gas into the main, at the junction of it with the eduction pipe is placed a regulating valve, and from the main is supplied a lamp kept constantly burning, whilst an attendant, by partially opening or closing the valve, maintains the flame of the lamp at the proper height.