74 CONSTRUCTION OF RETORTS. 



The FUEL used for heating the retorts may be either coal or coke, according 

 to the relative value of each in the district. If coal is used, a well-regulated 

 bench will require about 18 to 20 per cent, of the coal distilled ; that is to say, 

 to heat the retorts for the production of 12,000 cubic feet of gas, from 5 to 5^ 

 cwt. of coal will be necessary. The use of coke as fuel is more general, par- 

 ticularly in those places where coal is valuable, as in the neighbourhood of 

 London, and where coke is less in requisition as fuel for manufacturers. The 

 quantity of coke for heating the retorts will vary from 40 to 45 per cent, of 

 the quantity produced; that is to say, from 16 to 18 bushels of coke are 

 requisite to distil one chaldron of coal, or 5 cwt. will distil one ton. 



Mr. Croll, the superintendent of the Chartered Gas Company's works 

 (Brick Lane station), has introduced a system of using the coke as fuel while 

 red-hot. The charge from the retorts is drawn into a wrought-iron carriage, 

 and immediately taken to those furnaces which require feeding. He informs 

 me, that the saving effected by this simple process is equal to 10 or 12 per 

 cent. : I should conceive it to be fully that. The reason is evident ; because 

 when a quantity of black coke is thrown on the previously-heated mass of fuel, 

 the flues will to a certain extent become cool, since the heated air is absorbed. 

 When hot coke is thrown on, no absorption takes place, and the flues are 

 kept up at a uniform temperature. 



The use of tar as fuel has of late become frequent, and is the most cecono- 

 mical, as far as it is available. In almost every instance it is worth more to 

 burn than to sell, viz. 3d. per gallon. The quantity required for carbonizing 

 a chaldron of coal varies from 24 to 27 gallons. At the Pancras station of 

 the Imperial Gas Company each bench of retorts will carbonize about 60 

 bushels of coal in 24 hours, with from 40 to 45 gallons of tar as fuel. 



The furnace used for burning tar is the same as that used for other fuel, 

 and is fed by a small continuous stream, conducted by a wrought-iron service- 

 pipe, from a tank placed on the top of the retort-benches, on to a sheet-iron 

 spout projecting a few inches outside the furnace-plate, and into the furnace 

 itself, as shown in Fig. 18, where it spreads over a "breeze-bottom," pre- 

 viously brought to a red heat. At Galashiels Mr. Kemp uses a small force- 

 pump for supplying the furnaces with tar, by which means the heat is kept 

 up with great regularity. 



