HEATING-POWER. 107 



As fungi do not occur below one or two feet from the surface 



of the ground, and bacteria that assist greatly in destroying 



wood in contact with the soil are found only in its superficial 



layers and not in peat, deep immersion in the soil, or in peat, 



rves wood, as has been stated already. Tr.] 



0. Huat'uuj-poiccr ami Combustibility <>l' 



There are various methods for determining the heating- 

 power of wood. As burning wood takes oxygen from the air 

 and gives out carbon-dioxide and water-vapour, the mass 

 of oxygen requisite to burn a given mass of wood can be 

 measured : the more oxygen is needed for the combustion of 

 the wood, the more carbon the wood contains and consequently 

 the greater is its heating-power. The amount of oxygen may 

 be determined by burning the wood in a closed retort with a 

 metallic oxide (red lead). This chemical method does not 

 give the utilizable heating-power of the wood but only the 

 percentage of carbon it contains; the variations in the mass 

 of carbon in wood when measured by weight are small, 

 though if measured in volume, the results exhibit a steady 

 relation liet\yeen the heatin^-poNYer and specific weight of 

 wood. The average volumes of carbon, hydrogen, oxygen and 

 nitrogen in wood and other combustibles are given below : 



H. o. N. 



Wood ... 50 C 413-7 1*3 



Peat ... 59 C 34'5 0'5 



Lignite ... 68 5 26'6 0'4 



Coal ... 80 5 14'0 I'O 



Anthracite... 95 '2T> 2'0 0*5 



In physical methods for determining heating-power, the 

 wood is burned with free admission of unlimited oxygen ; 

 the mass of ice that is melted, or the quantity of water 

 that is converted into steam, by burning equal volumes of 

 different kinds 'of wood, is then ascertained. Also the rise in 

 temperature of a certain volume of water by the burning of 

 the wood may be measured. 



* Fritz, "Die Heizmaterlalen u. deren Ausiiut/mig." 1X77. Fuchaschmid, 



vri>clui<M|ener Hol/arteii." 



