110 



PROPERTIES OF WOOD. 



growth of fungi, which destroy the cell-contents and the walls 

 of the woody tissues. Decaying wood has little heating-power, 

 while rotten wood merely glows without any flame. 



Ethereal oils rich in carbon, such as turpentine, increase 

 the heating-power of wood. In the case of pieces of wood that 

 have nearly equal specific weights, their possible contents in 

 resin is decisive as to their greater or less heating-power. 

 The excellent book by Hempel and Wilhelm * gives the 

 following heating-powers for conifers, that of beech being 

 100, and confirms this statement for spruce and silver-fir : 



Abnormal contents of resin, as at wounds and in the stump- 

 wood of pines, increases the heating-power. Such wood is 

 used for torches. [Stump-wood of the longleaved pine, in 

 the Himalayas, also used for torches, is sometimes resinous 

 enough to be translucent. Tr.] 



Betulin increases the heating-power of the wood and bark 

 of the birch. When birch is cut into small pieces it gives 

 out heat rapidly, but the heat is not durable. Split birch wood 

 is much used by bakers. 



In utilizing the heat from wood there is much difference 

 in the various species. Woods which crackle and emit sparks 

 when burning, and most soft woods, rapidly develop an intense 

 heat of short duration. Such are larch, spruce, silver-fir, 

 peeled coppice oak, sweet-chestnut [also young pinewood 

 and broad leaved softwoods ; these woods are used in bakers' 

 ovens and for pottery and glass-making. Tr.] Woods which 

 burn slowly and quietly with glowing embers produce event u- 



* G. Hempel u. It. Wilhdni, "Die r>:iiime u. Straiicher des Waldes." Wien, 

 1900. 



t " Das Harz der Nadclljitev' Jiurlin, IS'.M. 



