100 TECHNiuAi. 1'i;oi'ERtif:.s of wood. 



coniferous wood, and are therefore in great demand for liakinjj;, 

 tilc-maldn<];, and other trades where a quick heat is required. 



Nordhngor states that when wood contains 45 per cent, of 

 moisture, it loses half its utilizable heating-power ; many 

 woods in winter contain up to GO per cent, of moisture, and 

 when burned green, only exert one-fifth of their heating-power. 

 The difference between combustibility and heating-power in 

 the green or dry state is not the same for all woods ; conifers, 

 when burned in the green state, give out relatively more heat 

 than green broad-leaved wood, chiefly owing to the resin they 

 contain, and among broad-leaved trees, alder and birch give out 

 most heat when burned green. [Silver-fir branches with the 

 needles on contain so much turpentine that a tire can be made 

 from them when freshly cut from the tree. — Tr.] It has often 

 been imagined that wood which has been floated for some time 

 loses a considerable degree of its heating-power, because it leaves 

 somewhat less ashes than unfloated wood. This circumstance, 

 however, can have no influence on its heating-power, and recent 

 investigations have proved that floatage is not appreciably 

 prejudicial to the heating-power of wood, provided it is 

 thoroughly and rapidly dried when landed. This latter condition 

 is frequently not secured, but the wood is often piled together in 

 heaps at the wood-depots, which are not so arranged as to aflbrd 

 thorough ventilation, and therefore the wood does not dry 

 quickly enough. It is owing to this fact that firewood brought 

 from the forest by land-transport is often preferred for heating 

 purposes to floated wood.* 



Steaming and boiling wood does not impair its heating-power, 

 provided the Avood 1)C thoroughly dried before being burned. 



3. A)iai()inical Stnicfiirc. 



The effect of the anatomical structure of the wood, indepen- 

 dently of its influence on the drying and density of the wood, is 

 also important, owing to the fact that the substance of porous 

 woods is more in contact with the oxygen of the air than that of 



* Brix fo\ind tliat 1 lb. lloatcd l.cctliwood lieatiil l-C lbs. of water from 32° into 

 steam, and lliat 1 lb. of imlloated bfechwood licatud 4-4 lbs. of water to the Siiiiu; 

 extent. 



