CHARCOAL-KILNS. 6U5 



of carbon and hydrogen with oxygen within the chamber. As 

 the construction of the chambers and the transport of the wood 

 are very costly, and the yield of charcoal is not always greater 

 than in kiln-burning, the method is only exceptionally employed, 

 and then chiefly to obtain secondary products, acetic wood, tar, 

 &c. Where wood-gas is used for illumination, charcoal is a bye- 

 product. 



Section II. — Charcoal-Kilns. 



A charcoal-kiln is a heap of firewood of a regular shape, and 

 with a covering, as eifective as possible for keeping the fire 

 inside the kiln and excluding atmospheric air. 



The shape is generally that of a paraboloid, and only in 

 certain cases that of a horizontal prism. Wood may be piled 

 in kilns either vertically or horizontally, and as these methods 

 of piling the wood, as well as the external form of the kiln, 

 give rise to considerable ditferenccs in the process of charcoal- 

 making, vertical and horizontal kilns will be separately described. 



In vertical kilns, the wood is piled nearly vertically around 

 stakes in the middle of the kiln, so that the latter assumes 

 the shape of a paraboloid. Horizontal kilns are distinguished 

 from the former kind by their prismatic shape and by the fact 

 that the charcoal is removed Irom them gradually as the wood 

 becomes carbonised. 



Although the comparison between these methods will follow 

 at the end of the chapter, it may here be mentioned that the 

 vertical arrangement of the wood is that usually followed as 

 experience shows that it gives the best results. A further dis- 

 tinction depends on whether the kilns are made in the forest, 

 and consequently in different places every year as the felling- 

 areas change, near iron-furnaces and other works using charcoal, 

 or in large kilns away from the forests. 



It is evident that in the last case greater care can be taken 

 and better results will follow than when kilns are burned in the 

 forest, frequently under very unfavourable conditions. In spite 

 of this disadvantage, however, forest charcoal-kilns are more 

 economical, as will be seen hereafter. 



