694 WOOD-CAHBONISATIOX. 



7,440 heat-units, ami wood 4,182. Its comparative facility of 

 transport is proved by the fiict, that the weight of charcoal is 

 only 25% of that of the same volume of wood. Owing to these 

 advantages, large quantities of timber in remote forests, which 

 were formerly not otherwise utilizable, were converted into 

 charcoal. Forests formerly existed in which the whole annual 

 yield of wood was converted into charcoal and used for smelting 

 iron, or in glass- or salt-works. In Europe at present, charcoal- 

 making has lost much of its former importance, as nearly all 

 heating and smelting processes are effected by means of coal 

 an<l coke. A considerable quantity of charcoal is, however, still 

 prepared, as the following figures show : — 



Imiiorts in cu)>. meters (1893). 



France 44,300,000 



Italy 10,600,000 



Spain 30,000,000 



Austria-Hungary and Germany each exported in the same 

 year 20,000,000 cubic meters of charcoal. 



Charcoal-dust is used in the manufacture of the well-known 

 briquets for fuel. 



There are three modes of charcoal-making, in pits, retorts 

 and kilns. Charcoal is usually made in kilns, so that only a few 

 remarks will be made about the other methods. 



The most wasteful way of making charcoal is in pits. A 

 circular hole is dug in fairly stiff soil, with inclined walls and a 

 depth of about a yard, it is then filled Avith dry branches. 

 These are fired and remain burning uncovered until they have 

 ceased to smoke and the wood has been converted into charcoal, 

 which is then pressed down and dry wood placed upon it. 

 The operation is repeated until the pit is full of glowing 

 charcoal. It is then covered with sods and earth, and the 

 charcoal allowed to cool ; in 1 or 2 days the pit may be opened 

 and the charcoal removed. This method which admits air 

 almost freely, is only justifiable where wood has scarcely any 

 value. 



Charcoal-making in retorts is jjiactised when wood is placed in 

 completely air-tight masonry, or iron, chambers and heated, 

 partly from outside by a furnace, and partly by the combination 



