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GAS, MANUFACTURE OF. 



GAS, MANUFACTURE OF. 



3oa 



it is bolted on to a species of saddle formed to receive it ; the diameter 

 at the bottom, in ordinary retorts, being generally about 6 inches, 



-. 



J 



and at the top 4 inches. In such cases the length of the stand-pipe ia 

 about 10 feet ; but the number of retorts in a bed muat naturally 

 affect this dimension. At the top of it there is fitted one end of a 

 short bent pipe, known as the If-pipe, or the bridge-piece, which by its 

 other end is connected with the descending pipe, and by it with the 

 hydraulic main ; the lower end of the descending pipe being carried 

 about two or three inches below the surface of the water and tar of the 

 main, and thus converted into a species of hydraulic seal, to prevent 

 the return of the gas to the retort after it has once risen through the 

 water. The H-pipes bear at the top a moveable cup. 



The hydraulic main is a species of iron trough, rather more than 

 half filled with water, which is sometimes carried on columns in front 

 of the mouthpieces of the retorts, but is, generally speaking, placed a 

 little within the line of the retort setting, so as to allow of its being 

 supported from the same. Whether the hydraulic main be within or 

 without the front line of the retort beds, it must run from one end of 

 the retort house to the other ; and under any circumstances it must be 

 kept sufficiently high to allow good head-room beneath it, and to 

 remove it from the direct action of the flames which escape when the 

 retorts are being charged. The dimensions of the main must be suffi- 

 cient to contain the quantity of tar and water which should be able to 

 close the immersed ends of the H-pieces when the mouthpieces of the 

 retorts are opened ; for at that period the pressure of the gas into the 

 main will cause the tar to rise in the pipe to a point depending upon 

 the pressure itself. Another condition to be observed in the con- 

 struction of an hydraulic main is, that the exit pipe should be placed 

 above the surface of the tar, in order to prevent any interference with 

 the passage of the gas to the condensers. A small outlet pipe is 

 inserted at the ends of the main, through which the surplus tar flows 

 into the tar cistern ; the lower end of this overflow pipe must be care- 

 fully sealed, in order to avoid any escape of gas through it. 



It would perhaps be dangerous in a general description of the process 

 of gas-making, to attempt to lay down the laws for the construction 

 afld dimensions of the furnaces and flues required for the purpose of 

 heating the retorts to the requisite temperature for the distillation of 

 the coal ; because the varieties in the dimensions of the retorts and of 

 the materials employed in their construction, as well as of the fuel 

 used for heating the retorts, render it necessary to introduce many 

 modification!) in the furnaces. The object to be attained is, to heat 

 cast-iron retorts to a uniform cherry-red heat, in the interior ; or to 

 heat clay retorts to a white heat, with the smallest possible expendi- 

 ture of fuel ; and, after all, much must be left in these matters to the 

 tact and skill of the operative engineer who fixes the work. It is 



AliTS ASD SCI. LIV. VOL. IV. 



usual, it may be here added, to calculate that, when retorts are heated 

 by the waste coke of the gas factory itself, about from 25 to 35 



per cent, of the coke made ia burnt under the retorts. Sometimes tar 

 is burnt in the furnaces ; but as the local markets for the residual pro- 

 ducts of gas-making constantly vary, it is not advisable to attempt to 

 discover any general law in respect of the nature of the fuel, any more 

 than it was in the case of the size and details of the furnaces and flues. 

 The mode of charging the retorts is another detail of the service of a 

 retort house in which many differences prevail ; for in small country 

 works, where it is important to keep down the outlay for labour, the 

 stoker is made to charge the-retorts by means of a shovel ; whereas, in 

 large works, the whole of the charge is frequently placed in a scoop, 

 and is inserted in the retort at once : the object to be attained in 

 either case being to distribute the coal for distillation in a uniform, 

 coat of about 5 inches in thickness all over the bottom of the retort, 

 and to leave the mouth open for the shortest possible time, in order to 

 avoid any unnecessary lowering of the temperature. There are, in 

 fact, few details in the process of gas-making of equal importance to 

 the regulation of the temperature of the retorts, and it is impossible to 

 call the attention of the workmen too forcibly to the subject. If, for 

 instance, the heat be maintained for any length of time at a very high 

 point, the retorts will be burnt out rapidly, and the proper quantity of 

 gas per ton of coal will not be obtained. If, on the other hand, the 

 heat of the retorts be too low, a large quantity of tar will be formed, 

 the quality of the gas will be inferior, and the rate of distillation will 

 be protracted. When the temperature of the retorts is properly regu- 

 lated, and the quality of the coals used is of an ordinarily good descrip- 

 tion, it may generally be calculated that a ton of coals will yield 

 between 8700 to 9300 cubic feet, measured by the station-meter before 

 being passed into the gas-holder. 



2. From the hydraulic main the gas passes at an average temperature 

 of 120" Fahr. into the condenser!. The condensers in the best modern 

 works are formed by means of a series of vertical pipes, whose lower 

 ends dip in water for the purpose of arresting the passage of the tar 

 can-led over, and which are connected by a second series of inclined 

 pipes passing from the bottom of the first vertical pipe to the top of 

 the second pipe. In its passage through these pipes the gas parts with 

 some portion of its heat by radiation (and therefore the diameter of the 

 vertical pipes should be made as large as possible) until at last, at the 

 final exit pipe, the gas is lowered in temperature to about 60" (but 



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