OBTAINING THE CONSTITUENTS OF WOOD. 525 



shavings and resin, or coal-tar. Artificial wood is made of 

 peat mixed with lime and sulphate of alumina in solution. 



C. CHANGES IN THE SUBSTANCE OP THE WOOD 

 IN ORDER TO OBTAIN ITS CONSTITUENTS. 



SECTION I. BY HEAT. 



The first chapter on the properties of wood explains the 

 action of heat on wood. Where wood is burned and oxygen 

 admitted freely, light, heat and gases (CO^ and H 2 0) are 

 produced ; combustion is maintained by the hydrocarbon 

 gases, light by the glowing of the charcoal, and ashes form 

 the residue. If the wood is burned without free admission of 

 oxygen, it is said to be roasted with dry distillation, under 

 which are preserved gases and carbon, with numerous other 

 products of incomplete combustion, all empyreumatic sub- 

 stances of great economic value. 



Although properly an account of these substances does not 

 come under the direct activity of a forester, yet he should 

 possess a general knowledge of the products of distillation of 

 wood, as well as of all matters which bear on the sale and 

 value of wood, the chief product of his calling. 



1. Distillation of Wood* 



The apparatus for distilling wood varies with the products 

 to be obtained from it. If gas and volatile products are 

 required, the wood should be roasted in vessels with open 

 tubing from which those products can escape, in order to be 

 received in a refrigerator, or to pass through it purified. 

 Such apparatus consists of boilers, retorts and stoves. If 

 heavy liquids and solids are the chief desiderata, the wood is 

 usually piled in large covered heaps, charcoal-kilns or pits. 



When wood is distilled in retorts or vessels, according to 

 Violette, the decomposition of the wood begins at a tempera- 

 ture of 160 C. ; the condensed vapours yield a yellowish, 

 aromatic, bitter liquid. At 280 the weight of this liquid is 

 64% of the weight of the original wood; products that are 



* J. Bersch " Die Verwertung des Holzes auf chem. Wege,'' '2nd ed. 1893. 



