[PLATE VII.]
Exhibits a perpendicular section of a gas-light apparatus, calculated for lighting towns, or large districts of streets and houses.
[Fig. 1.] The Retort Furnace. The retorts are placed over each other in one or more rows; so that a certain number of them may be heated by separate fire-places. A, A, shows two of the retorts placed horizontally above each other; B, the fire-place; C, the flue which causes the fire to circulate round the retorts so as to heat them equally in every part; D, the opening of the flue where the fire passes into the chimney; E, the ash-pit; F, a chamber in front of the retort furnace, into which the orifice or mouth of the retorts project; G, G, the doors of the chamber, to enable the workmen to charge and discharge the retorts; H, a funnel shaped hole at the floor of the chamber F, through which the red hot coke as it is discharged from the retorts passes into the arched vault I; K, the syphon tube; L, the horizontal condenser[41]—the action of both of these pipes have been already explained, [p. 168]; M, main pipe, which conveys the liquid substances from the condenser, to the tar cistern, [fig. 3], and which conducts also the gazeous products into the lime machine, [fig. 2]; N N, shows that part of the pipe which is interposed between the tar cistern, [fig. 3], and the condensing pipe M,—it passes in a serpentine direction along the inner sides of the gasometer cistern, and, like the so-called worm in a distillatory apparatus, condenses the products which escape in a vaporous state from the condenser L; O, shows the place where the serpentine pipe N N, passes again out of the gasometer cistern, and its communication with the lime machine, [fig. 2], and tar chamber, [fig. 3]. The action of the lime machine is as follows: The liquid products evolved from the coal, having been deposited in the tar cistern, [fig. 3], by means of the serpentine pipe N, N, the gazeous products which accompany it, are conveyed by means of the pipe P, which branches out from the pipe O, into the interior receptacle of the lime machine marked Q, which consists of a vessel open at the bottom, and closed at the top, where it communicates with the pipe O. As the gas accumulates in the interior part Q, of the lime machine, it is made to pass through the liquid which it contains, namely, slaked lime and water; and escapes through appertures made in the horizontal partitions R, R, R, R, into the outer vessel, S, of the lime machine and from thence it is conducted away by the pipe T, T, T, into the additional washing apparatus, of the gasometer; [fig. 4], the construction of this apparatus, greatly resembles the lime machine, [fig. 2], namely, V, is a water pipe, proceeding from a cistern U, placed 3 or 4 feet above the orifice of the pipe V; T, T, is the gas-pipe, covered with a hood, marked W, and immersed in a small cistern, having horizontal perforated shelves, like those in the lime machine—they fit close to the hood. The gas which enters the hood W, meets with a shower of water delivered by the pipe V. The gas, as it passes through the holes in the horizontal partitions, is, therefore, again washed and thoroughly purified from foreign gases which may have escaped the action of the lime machine; Y, is a waste pipe, the lower extremity of which is sealed by being immersed in water,—it serves to carry away the water delivered by the pipe V, as it has been acted on by the gas. The summary action of this gas apparatus is, therefore, as follows: The liquid products obtained from the coal during the distillation are first deposited in the main condenser L, by means of the pipe K, and from whence they cannot escape until a quantity of tar has accumulated in it to a certain height, and by this means, one of the extremities of the pipes K, K, becomes immersed and hermetically sealed by the liquid which the condenser L, contains. The liquid products, after having accumulated to a certain height in the condenser, overflow the perpendicular portion which it contains, and discharge themselves into the pipe M, from whence they are transported into the tar cistern, [fig. 3], by means of the system of pipes N, N, O, whilst the gazeous products are made to pass by means of the branch pipe P, into the lime machine, [fig. 2]. From this part of the apparatus the gas passes through the pipe T, T, T, into the additional or smaller washing apparatus placed upon a tressel in the cistern of the gasometer, where it is again exposed a second time to the action of a current of fresh water; and from this vessel the gas ascends into the gasometer. The gasometer is furnished with a pipe A, closed at the top, and fixed in one corner of the gasometer, but open at the bottom; it includes another pipe marked B, which communicates with the main pipe leading to the burners, or place where the gas is wanted. The pipe A, which slides over the pipe B, is perforated at the top, the gas passes through these perforations and is thus made to enter into the pipe B, and disposed of as mentioned. C, C, is a tube of safety adapted to the gasometer; its lower extremity remains sealed by the water in the cistern so long as the gasometer is not overcharged with gas; but, if more gas should be made to enter the gasometer than it is destined to receive, this pipe then delivers the gas into the funnel-shaped tube D, which reaches through the roof of the gasometer house, and thus the superfluous quantity of gas is conveyed away into the open air.
[41] The condenser in this apparatus is placed at right angles to the row, or rows of retorts. It is furnished at one extremity with a partition placed perpendicularly, and of a height equal to about one-half of the diameter of the condenser. The object of this partition is to prevent the tar, &c. deposited in it, to seal the pipes K, K, and not to discharge itself into the pipe M, till this has been effected. The partition is seen in the drawing.
The cylindrical vessel P, of [fig. 3], surrounding the orifice of the pipe O, which delivers the tar into the tar cistern, [fig. 3], serves to keep this pipe constantly immersed into a portion of tar, so that the contents of the cistern may be drawn off by the cock without admitting air into any part of the apparatus. The tar cistern has a small hole at the top, to allow the air which it encloses to escape, as it becomes filled with tar and ammoniacal liquor. The main condenser L, is placed, as shown in the drawing, higher than the level of the water in the gasometer cistern, to allow a free descent of the distillatory liquids as they pass from this vessel along into the pipes M, N, O, &c. The cistern of the gasometer, as well as the lime machine, and tar cistern, are constructed of cast iron plates, bolted and cemented together with iron cement. The gasometer is made of sheet iron plates rivetted together—E, E, are two iron stays—G, G, are friction wheels.
METHOD of correcting the relative pressure of the Gasometer, so as to cause the gas which it contains to be uniformly of an equal density.[42]
[42] For this elegant contrivance we are also indebted to Mr. Clegg.
We have mentioned already that the pressure of the gas in the gasometer should be invariable, for it is obvious that the weight of the gasometer is constantly increasing in proportion as it fills with gas, and rises out of the water—see [p. 88], and [167]. To render its pressure uniform, we first take the absolute weight of that part of the gasometer which becomes immersed in the water, and knowing the specific weight of the substance of which it is composed, we divide its absolute weight by the specific weight of the substance of which it is composed; and this being done, we make part of the chain, (measured at right angles from the axis of the wheels over which it passes downwards towards the top of the gasometer,) which is equal to the length of that part of the gasometer which becomes immersed in water, equal in weight to the specific gravity of the substance of which the gasometer is composed. For example, let us suppose that the part of the gasometer which becomes immersed in water weighs 861 lb. and that it is composed of sheet iron, the specific gravity of which, in round numbers, we will take to be 7. It is then evident, that the part of the chain of the gasometer measured downward from the axis of the wheel over which it passes, and which is equal in length to the height of the gasometer, must be loaded with a weight of, or must itself weigh, 123lb. for this would be the weight of the water displaced by the gasometer; or let us suppose the gasometer to be made of sheet copper, the specific weight of which (omitting decimals) is 8; and that the absolute weight of the gasometer is 1792lbs. then the chain of the gasometer equal in length to the height of the gasometer, immersed into the water must weigh 224lb. for this would be the weight of the quantity of water which the gasometer displaces. This being accomplished by then adding or diminishing the absolute or balance weight of the gasometer, any desired uniform pressure may be effected, and the same bulk of gas will always be of the same specific gravity.