GAS, COAL 



573 



near the bottom of tlio cylindrical vessel, which sits on the solo of the tar-cistern. 

 From the other side of the vertical branch/, the main pipe proceeds to the condenser 

 D, and thence by the pipe /, into the purifier E ; from which the gas is immediately 

 transmitted by the pipo p into the gasometer F. 



The operation proceeds in the 

 following way : As soon as gas 

 begims to be disengaged from the 

 ignited retort, tar and ammo- 

 niacal liquor are deposited in the 

 cylindrical receiver B, and fill it 

 up till the superfluity runs over 

 by the pipe d, the level being 

 constantly preserved at the litio 

 shown in the figure. By the 

 same tarry liquid, the orifices of 

 the several pipes b, issuing from 

 the retorts are closed ; whereby 

 the gas in the pipe d has its 

 communication cut off from the 

 gas in the retorts. Hence, if one 

 of the retorts be opened and 

 emptied, it remains shut off from 

 the rest of the apparatus. This 

 insulation of the several retorts 

 is the function of the pipe under 

 B, and therefore the recurved 

 tube 6, must be dipped as far 

 under the surface of the tarry 

 liquid as to be in equilibrio with 

 the pressure of the gas upon the 

 water in the purifier. The tube 

 b is closed at top with a screw 

 cap, which can be taken off at 

 pleasure, to permit the interior 

 to be cleansed. 



Both by the overflow from the 

 receiver B, and by subsequent 

 condensation in the tube d, tar 

 and ammoniacal liquor collect 

 progressively in the cistern or 

 pit under c, by which mingled 

 liquids the lower orifice of the 

 vertical tube/ is closed, so that 

 the gas cannot escape into the 

 empty space of this cistern. 

 These liquids flow over the edges 

 of the inner vessel when it is 

 full, and may, from time to time, 

 be drawn off by the stopcock at 

 the bottom of the cistern. 



Though the gas has, in its 

 progress hitherto, deposited a 

 good deal of its tarry and ammo- 

 niacal vapours, yet, in conse- 

 quence of its^ high temperature, 

 it still retains a considerable 

 portion of them, which must be 

 immediately abstracted, as other- 

 wise the tar would pollute the 



lime in the vessel E, and interfere with its purification. On this account the gas 

 should, at this period of the process, be cooled as much as possible, in order to con- 

 dense these vapours, and to favour the action of the lime in the purifier E, upon the 

 sulphuretted hydrogen, which is more energetic the lower the temperature of the gas. 

 The coal-gas passes, therefore, from the tube / into the tube k of the condenser D, 

 which is placed in an iron chest g, filled with water, and it deposits more tar and 

 ammoniacal liquor in the under part of the cistern at t, t t When these liquids havo 



