CONSTRUCTION OF RETORTS. 91 



Manchester, one of the most enlightened towns in the kingdom for mechanical 

 and chemical science, this valuable instrument was for a long time expressly 

 forbidden to be used, although five years afterwards the Directors were com- 

 pelled to acknowledge that the great success of the Manchester works was 

 chiefly attributable to the Meter. 



In England and Scotland the fire-clay retort has superseded the use of 

 metal in no less than forty towns ; in some instances it has lasted for the 

 extraordinary period of twelve years ; while, during this time, at all other 

 works where the invention is not yet used, it may be asserted that iron retorts 

 have been renewed as many times. The oven or D-shaped retorts are found 

 to be the most advantageous, being made with a capacity to carbonize one 

 cwt. of coal every hour. They can be constructed either to be heated by 

 coke ovens, or coke furnaces, or by the burning of tar : with coke ovens they 

 are more durable. It appears that clay retorts, when constructed upon such 

 a scale as that given in the Plate, have great power to retain their heat 

 when brought to the proper temperature for decomposing the coal, viz. 27 

 of Wedgewood, and the introduction of a fresh charge is not nearly so much 

 felt by them as by metal ; this is a practical point one which I have been 

 at much pains to ascertain, and which I would not state were I not con- 

 vinced of its correctness by personal observation. Mr. Grafton afforded me 

 every facility for experiments, and is willing to do so to all who have a desire 

 to test his retorts. This power of retaining heat is proved by constant practice 

 to produce 1000 cubic feet of gas per ton from the same coal more than the 

 average of the London produce, and the consumption of fuel is not more 

 than 22 or 23 Ibs. of coke to carbonize 100 Ibs. of Newcastle coal, taking 

 the average of six months' working: it is even less with the Staffordshire or 

 Lancashire coal. 



When properly constructed, these retorts are not in any degree liable to 

 fracture or to the escape of gas, but are of such strength as to resist the 

 greatest pressure which is likely to be put upon them. The coke also made 

 by them is invariably of better quality, and produces less breeze or waste. 



The advantages of the fire-clay retorts, combined with their great durability, 

 will ere long be generally acknowledged, and their use will consequently be 

 more extensive. At the gas-works in Cambridge, where from the beginning 

 this kind of retort has been adopted in every variety of form, no retort has 

 been changed nor any new one erected for four years. The oldest in that 



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