CONSTRUCTION OF RETORTS. 



75 



Fig, 18. 



When retorts have been at work for some months, their interior surfaces 

 become incrusted with a hard carbonaceous deposit, approaching, in some of 

 its properties, to plumbago ; in process of time carburet of iron and the more 

 infusible parts of the coke form a thicker crust, which it becomes necessary 

 to remove, both to prevent the destruction of the retort, and to allow the fuel 

 to have full effect upon the coal contained within. This was formerly effected 

 with great difficulty by crow-bars, the force required often increasing the evil 

 it was intended to remedy. 



It was afterwards found, that leaving the retort open, and allowing cold air 

 to come in contact with the heated interior, the deposit contracted, and could 

 be broken away in about twelve hours without danger to the retort. 



Mr. Kirkham, the engineer to the Imperial Gas Company, in order to take 

 off this crust without endangering the retorts, employs an air-blast, which is 

 both speedy and efficacious in its operation. His method of conducting the 

 process is as follows : A cast-iron pipe, about three inches in diameter, is 

 carried along the front of the benches, at a little distance above the upper 

 retorts ; at points in this pipe, directly over every retort, a screw and plug is 

 attached, into which screw, when the plug is removed, a wrought -iron service, 



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