202 CAEBONISATION IN EETOKTS AND CLOSE OVENS. 



two English forms described above, but their object is principally 

 to obtain a good yield of pyroligneous acid. 



Apparatus have also been invented for distilling sawdust. Ow- 

 ing to its finely divided state, sawdust cannot be distilled in the 

 ordinary retorts, as it forms a dead mass and becomes carbonised 

 only superficially. For this reason, the sawdust is fed into the 

 retorts very gradually, and is constantly moved on, on an endless 

 iron band, until it finally leaves the retort at the other end in a 

 fully carbonised condition. The charcoal is comparatively useless, 

 but it may be made up into patent fuel. 



Very successful carbonization may be effected in ovens built 

 entirely of brick masonry and ending in a narrow chimney. Such 

 ovens may be made large enough to take up to 6,000 cubic feet of 

 wood. The wood is carefully packed inside, several vertical flues, 

 filled loosely with the smaller pieces, being formed, in order to 

 secure a free through-draTight and to distribute it uniformly. Just 

 enough air is admitted through the sole of the furnace to carbonize 

 the wood. The products of distillation pass out into convenient 

 receptacles through openings at the sole of the furnace. The car- 

 bonization is complete when the smoke issuing from the chimney 

 turns from black to a bluish white. . ' 



The great disadvantage attacliing to all fixed works is that the 

 wood to be carbonized has to be carried to them, often at prohibi- 

 tive expense. Hence their general inapplicability, except when the 

 products of distillation obtained serve to cover the increased ex- 

 penditure. 



To overcome this drawback various portable apparatus have 

 been devised, two of which are described below. One of these, 

 designed with the double purpose of effecting carbonization and 

 securing the products of distillation, is M. Moreau's patent. It 

 consists of a cast-iron furnace, having the shape of an octagonal 

 prism and capable of containing about 400 stacked cubic feet of 

 wood (roughly about 120 maunds). Tubes fixed at the top carry 

 off the products of distillation, while ingeniously designed self- 

 acting valves at the bottom allow of the wood inside being lighted, 

 as well as regulate the entry of air to keep up the combustion, the 

 valves completely closing of themselves when this becomes too 

 active. The whole apparatus can be quickly taken to pieces, and 

 transported and set up again with ease. The carbonization is com- 

 pleted in 30 hours, and the yield, by weight, of charcoal is said to 

 reach 23 to 24 per cent. 



Another apparatus, the invention of M. Dromart, consists of a 

 beehive-shaped oven, capable of containing about 800 stacked cubic 



