CARBONISATION IN RETORTS AND CLOSE OVENS; 201 



fire, the products of combustion, witli the heated air, are made to 

 circulate in an enclosed space, between the oven and the floor of 

 a drying room above, before passing up the shaft of the chimney. 

 In this drying room is stacked the wood to be carbonized after- 

 wards. Any number of ovens may be set up side by side in the 

 same building. The condensed products of the distillation are 

 delivered into a tank, where the tar settles down to the bottom 

 and is drawn off, while the supernatant liquid, after the lighter 

 tarry and carbonaceous matters which rise to the top have been 

 skimmed off, is pumped up into a reservoir containing a solution 

 of lime or soda to form the acetates, from which the pure acetic 

 acid of commerce may then, if required, be distilled after admixture 

 with sulphuric or hydrochloric acid. When the run of liquid from 

 the condenser ceases and the exit pipe from the cylinder becomes 

 cool, it is known that the distillation, in other words, the carboniza- 

 tion, is complete. The fires are allowed to die down, the door is 

 opened, and the charcoal raked out into a deep iron waggon with 

 a close iron cover, which is luted down with clay to prevent the 

 charcoal from taking fire in contact with air. 



In some other works in England, instead of the cast-iron cylin- 

 ders, they use more or less square ovens, into which the charge is 

 introduced in sheet-iron waggons. The waggons are filled up to 

 about 18 inches above the sides ; with the progress of carbonization 

 the contents ultimately subside below the sides. In this method 

 the charcoal is at once withdrawn in the waggons and thus runs 

 no risk of breaking. 



The disadvantages of the cast-iron cylinders are a liability to 

 crack, and a larger consumption of fuel owing to the thickness of 

 the plate. On the other hand, the wrought-iron ovens are apt to 

 leak at the joints and doors, to warp with the heat, and to be more 

 quickly corroded by the acid products of the distillation. The 

 yield of charcoal in both kinds of apparatus slightly exceeds 25 

 per cent, of the weigbt of well-seasoned wood ; but this of course 

 leaves out of account the fuel consumed below the cylinder to 

 effect carbonization. 



A form of apparatus much used in France consists of a cylindri- 

 cal cast-iron retort, which, after being charged and closed, is hoist- 

 ed into a close-fitting brick furnace or jacket with a fire-place at 

 the bottom, A strong air-tight cover is put over the furnace. 

 As soon as the distillation is finished, the retort is hauled out and 

 a fresh one put in. In another very convenient form of apparatus, 

 M. Kestner's patteirn, the retort is fixed and built round with 

 masonry. Both patterns are very simple and less costly than the 



2 B 



