GAS, COAL 



579 



1038 



temperature ought to be only a few degrees higher than that of the atmosphere, 

 except in winter, when it is advisable to maintain a heat, relatively to the external 

 air, greater than in summer. The gas leaves the retort by the standpipes, A A A, 

 fig. 1038, which are of cast iron, 

 o inches in diameter at their lower 

 extremity, and slightly tapering up- 

 wards. Some of the least volatile 

 products of decomposition condense 

 in these pipes, but their proximity 

 to the furnaces, and the constant 

 rush of heated gas and vapour 

 through them prevent more than a 

 very slight amount of refrigeration. 

 They conduct to the hydraulic main, 

 which is shown at B, fig. 1038. It 

 consists of a cylinder running the 

 entire length of the retort-house, 

 and fixed at a sufficient height above 

 the mouths of the retorts to protect 

 it from the flame issuing from the 

 latter during the times of charging 

 and drawing. The diameter varies 

 from 12 to 18 inches, and the re- 

 curved extremities of the stand- 

 pipes (the dip-pipes) c c c c, pass 

 through it by gas-tight joints, and 

 dip, to the extent of 3 or 4 inches, 

 into the condensed liquids contained 

 in the hydraulic main. The use of this portion of the apparatus is to cut off the 

 communication in the reverse direction between the gas beyond the standpipes and 

 the retorts, so as to prevent the former rushing back down the standpipe during the 

 time that the lid of the retort is removed. Being maintained half full of tar it 

 effectually seals the lower ends of the dip-pipes, and prevents any return of gas towards 

 the retorts. The condensed products, consisting chiefly of tar, make their exit from 

 the hydraulic main by the pipe D, which leads them to the tar-well. From the 

 hydraulic main the gas passes to the condenser, the office of which, as its name 

 implies, is to effect the condensation of all those vapours which could not be retained 

 by the gas at the ordinary atmospheric temperature. The condenser has received 

 a variety of forms, but the one which appears to unite in the highest degree sim- 

 plicity and efficiency, is the invention of Mr. "Wright, of the Western and Great 

 Central Gas Companies. Its construction is shown \nfig. 1039. AAAA, are 5 double 

 concentric cast-iron cylinders, through which the air is made to circulate in succes- 

 sion by means of the tiepipes B B B B, whilst the inner cylinders being open above and 

 below, a current of air, set in motion by their heated walls, rushes through them, 

 thus securing both an internal and external refrigeratory action. It will be also seen 

 by a reference to the figure that the heated gas enters these cylinders at the top, 

 taking an opposite direction to that pursued by the external and internal currents of 

 air, and thus securing the most perfect refrigeration, by bringing the gas constantly 

 in proximity to air of increasing coldness. Each cylinder is furnished at bottom with 

 a tar receptacle, c, for the collection of the condensed products, which are carried to 

 the tar- well by a pipe not shown in the figure. The details of construction are suffi- 

 ciently seen from the drawing, and require no further description. 



In some country works the condenser represented at D, fig. 1026 (p. 573) is used. 

 It consists of a square chest, g, made of wrought-iron plates open at top, but having 

 its bottom pierced with a row of holes, to receive a series of tubes. To these holes 

 the upright four-inch tubes h h are secured by flanges and screws, and they are con- 

 nected in pairs at top by the curved or saddle tubes. The said bottom forms the 

 cover of the chest 1 1, which is divided by vertical iron partitions, into half as many 

 compartments as there are tubes. 



These partition plates are left open at bottom, so as to place the liquids of each com- 

 partment in communication. Thereby the gas passes up and down the series of tubes, 

 in proceeding from one compartment to another. The condensed liquids descend into 

 the box 1 t, and flow over into the tar cistern, when they rise above the level t t. The 

 tar may be drawn off' from time to time by the stopcock. Through the tube k cold 

 water flows into the condenser chest, and the warm water passes away by a pipe at its 

 upper edge. 

 , The extent of surface which the gas requires for its refrigeration before it is admitted 



