Before we proceed to enter into any particulars relative to the practice of gas lights, we shall give a more minute description of the apparatus, in reference to the Plate. Fig. 1. Plate CCLX1V. is a plan and section of the furnace containing the retort. The latter is seen to more advan tage in the perspective view. In Fig. A, e e e are project ing pieces marked similarly in Fig. 1, for the retort to rest in a horizontal position: ji is the place where the two parts of the retort are screwed together. The front part contains two ears t t. Pig. B is the lid or cover, having a conical edge, which fits the mouth of the retort, and is forc ed into its place by a wedge Fig. C, which passes through two holes in the cars t t ; s is a pipe, with a plunge to re ceive the pipe n, (Fig. 2.) being cast with the front part of the retort. The fire-place is shewn at in (Fig. 2.), d is the door, g the grate, A the ash-pit, and f the flue. The flame first passes along the flue under the retort, where it reaches r, and rises to the upper side of the retort, and passes, in the direction of the returning darts, into the chimney C. The separation of the lower half of the flue from the upper is seen in Fig. S. at f f; bb are long fire bricks, which separate the fire place from the bottom of the retort ; this prevents the immediate action of the flame upon the retort, winch would soon destroy it. The retort, notwithstanding this apparent power, ultimately receives the whole of the heat without being liable to oxidation. When the retort is charged, and the lid secured, the gas and the other volatile products rise through the pipes s and n, and enter the large pipe c, which is called the conden se•; see Fig. 7. A portion of the tar, &c. condenses in this vessel, till it rises to the level of the pipe i, along which the gas and tar descend through a succession of pipes, pass ing round the inside of the vessel AB, which is filled with cold water. This vessel is square, so that the pipes pass ing along its sides are of equal length. They are so in cdned to the horizon, as to come to the point v when they have passed quite round the vessel. The pipe v x now brings it out at the point x. This pipe continues its direc tion into the vessel, Fig. 6. which cannot be seen in the profile, Fig. 7. The gaseous products rise up the pipe h, Fig. 7. and then descending, terminates in the vessel L; the plan of which is Fig. 5. The tar and ammoniacal li quor condense in the vessel, Fig. 6. which is called the tar vessel. It is made perfectly air tight, and its contents are drawn off at an aperture on a level with the bottom, so that no air can escape till the whole of the liquid is dis charged. We now return to the gaseous products, which enter the vessel L ; and in order the better to see how they are disposed of, it will first be necessary to describe its office. The vessel in Fig. 7. is a reservoir to contain a mixture of lime and water, for the purpose of supplying the vessel L. The vessel in is of a limited depth, in order just to supply the vessel L to a certain height. The trans fer from in to L is made by means of the pipe p, by draw ing out the plug 8. As soon as the vessel L has received its proper quantity, the plug is replaced. The gas enters at o. The lime water, which now stands at the level of the top of the vessel in, is pressed down to the point d. The same quantity, rising along the passage d reaches to the point g. The gas now enters at d, and passes to e, then returning, ascends to f, from whence it rises up tog, where it enters the pipe b c, and the larger pipe 1, which surrounds b c. The pipe / is closed at the top, but below the height lit is perforated with a number of holes. The vessel AB is filled with water up to the lower extremity of the vessel D. When the gas has passed out at the top of b c, it displaces the water in /, which is on a level with that in AB, till it sinks to 1. It now escapes at the holes above mentioned, and bubbles through the water. In this state it is preserved in the gazometer, and is fit for burning. The gazometer we shall now explain more particularly. It may be first proper to return to the lime vessel L. The cavity d efg is formed by six plates of iron, lead, or wood, of the width of the vessel L, arranged in pairs parallel to each other, forming cells, which contain a stratum of fluid three inches thick, fifteen inches wide, and of a length equal to d e added to e f added tof g. This cavity, and the space L, constitute the whole of the capacity of this vessel, which is employed for the liquid, the rest being shut out by the partition S d, and the plates forming the zig-zag cavity. The gazometer, which receives the gas after it has been purified by the lime water, consists of an outer vessel AB filled with water. It is made of cast iron plates screwed together by flanges. D is a vessel made of plate iron, the plates being united by rivets. This vessel, in an inverted position, falls and rises in the outer vessel as more or less gas is contained in it. For this purpose it is suspended by chains, which pass over the pullies 1, 2. The ends of both these chains arc fastened in separate grooves in the edge of the pulley 11I, which is of such a diameter that the ves sel I) rises to its full height before the pulley makes one revolution. In another groove in the edge of the pulley AI,
is fastened the end of a second chain, to which the weight W is suspended. This weight is nearly equal to the weight of the vessel D, and assists it in rising as the gas comes under it. It will be evident, that when the whole or the vessel D is immersed in the water, it will become as much lighter as is equal to its own bulk of water. The vessel will therefore require a greater counterpoise as it rises higher, and will be the heaviest when it is at the top. 'ibis is compensated by forming the groove in the pulley 1\1, which contains the weight chain, so as to make the radii of the wheel change reciprocally with the relative weight of the vessel D, by which the pressure of this vessel, which is always a little heavier than the weight, will be uniform in every part of its ascent and descent. Before the gas can be admitted, the vessel D is allowed to descend to the bot tom of the vessel AB, which is effected by opening the stop cock y in the pipe z q y, which opens into the gazometer above the water. The common air is expelled, and its place occupied by water. The cock y is now shut, and the gazometer is ready to receive the gas.
We have already traced the progress of the gas to the lime vessel, where it is purified. It now rises through the pipe b c, as has been already described. When the cock y is opened, the preponderating weight of the vessel D forces the gas along the pipe z q y, from which it is con veyed by other branches into situations where the light is required. The pipes T and t are firmly inserted into the top of the vessel D, and in their motion up and down con stantly envelope the tubes b c and q z. They are for no other purpose than keeping the vessel D steady in its as cent and descent. That part of each projecting above the vessel forms a recess for the reception of the ends of the pipes b c and z q, in order that the mouths of the latter may be above the water, when the roof of the vessel D comes to the surface. 'Without this contrivance, the whole of the common air at the commencement could not he expelled. It will be easy to sec, that, from improper management, the gas may, under some circumstances, come over so ra pidly as to raise the vessel D quite to the top, and, still ac cumulating, would bubble out at the lower edge of the ves sel. Such gas mixing with the common air of the room, would be liable to explode by the light of a candle ; indeed, several serious accidents have already happened from this cause. There are several ways of avoiding the danger at tendant on this circumstance, but the most effectual we have yet seen, we shall explain by Fig. 8. AB is a sec tion of the outer vessel of the gazometer, D the inner ves sel, p a pipe inserted in the top of the latter, open at both ends ; the lower end being above the surface of the water, while the vessel D remains a little immersed. The part b c is a portion of a larger tube, with a bottom which is perforated to receive the pipe fi, to which it is soldered, so as to form a recess capable of holding water, and hence has been called a water-lute. When another pipe, such as j; has been placed in the recess filled with water, a gase ous fluid passing up jr, would be induced to pass through f, if not resisted by a force less than the column of water at the recess b c. It will now be evident, that if the tubef be fixed in the roof of the building, and open at both ends, when the vessel D rises till the recess b c receives the end of the pipe f, that the lower end of It will be' above the water. The gasshill therefore rise through fi, and pass forward through /into the open air, and thus prevent its escape into the room.
In carrying on the process, the water in the vessel AB will frequently require to be changed, as well from being contaminated with the remaining impurities of the gas, as from becoming warm by the pipes from the retort passing through it. Where water is very plentiful, it would be ad visable to have a constant current of warm water from the top of the vessel, and a cold current in at the bottom. The lime-water in the lime-vessel L, Fig. 7, will require chang ing much oftener than in the vessel AB. The sulphure ous acid, carbonic acid, and sulphurctted hydrogen, which come with the carburetted hydrogen, are all taken up by the lime, forming sulphate, carbonate, and hydrosulphuret of lime. From this it will be obvious, that the lime will ultimately be all consumed ; but it should be removed long before it arrives at complete saturation. The mixture of lime and water in the vessel 7/2 should be about the thick ness of cream, and hence has been called the cream of lime. When the liquid in the vessel L requires to he changed, the plug k is taken out, while the plug s is kept secure. When the vessel L is emptied, the plug k is replaced, and the plug s taken out. The fresh lime and water in /72 is now transferred to L; the proper quantity being as much as will run in till 772 remains full. It must be here observed, that the vessel in is rather a measure with which to fill the 'vessel L to a proper height, than a reservoir. It is hence supposed to be supplied from a large cistern, in which the cream of lime is prepared in considerable quantity.