64 FOREST UTILIZATION 



(d) 



Chestnut 

 Longleaf pine 

 VII. Heating power. 



Heating power or fuel value bears a direct ratio to specific 

 gravity air dry. All wood fibre having the specific gravity 

 1.56, equal air dry weights of our common species furnish 

 equal heat. On the other hand, light weight means greater 

 inflammability and a quicker heat, which naturally lasts for 

 a short time only. The heating power of hard coal is to that 

 of lignite and to that of wood as 5.2 : 4.3 : i. In other 

 words, 5.2 Ibs. of dry wood yield as much "heat as 4.3 Ibs. of 

 lignite or as I Ib. of coal. 

 Influencing factors are found in the following moments : 



(a) Presence of rosin increases the heating power by 



about 12%. 



(b) A cord of wood containing 45 % moisture has, after 



German experiments, the heating power of half a 

 cord of air .dried wood. After Sargent, the dis- 

 crepancy is not as great. One cord of green wood 

 contains 250 gallons of water, and the calories of 

 heat required to convert this large amount of 

 water into steam are lost for heating purposes. 



(c) Unsound wood has a reduced heating power, the cell 



walls being decayed. 



(d) Chestnut, and to a certain extent larch and spruce, 



are despised in open fires owing to crackling and 

 emission of sparks.. Black gum is despised be- 

 cause it is difficult to split and/ therefore difficult 

 to season. Hornbeam, birch and alder are said to- 

 furnish a particularly quiet flame. 



(e) Schedule of the heating power of wood per cord: 



IX. Miscellaneous technical qualities of wood. 



(a) Adaptability to planing and molding; varnishing 

 and polishing; painting and gluing. 



