10:! TECHNICAL rROPEllTlES OF WOOD. 



5. Soundness. 



The soandness of wood also considerably influences its 

 heating-power ; rotten wood has probably lost at least half of 

 its woody substance, owing to the ravages of fungi, and has a 

 light specific gravity and very little heating-power. 



Since, as a rule, young wood is sounder than old wood, fire- 

 wood from young broad-leaved trees has usually greater heating 

 power than when taken from old trees. It appears that when 

 wood rots, it first loses its hydrogen, for fallen dead wood burns 

 with a very slight flame. Even when perfectly sound, young 

 broad-leaved wood, and especially that of the beech, has a 

 greater heating-power than old wood, and especially than very 

 old wood. 



In the case of conifers, as the amount of resin they contain, 

 especially in the case of pines, varies with the age of the tree, 

 old coniferous wood generally has a greater heating-power than 

 young coniferous wood. 



0. Jh:tcn)iiiuiti(iii of Jlcdtinii-l'iuccr. 



Attempts have often been made to ascertain by experiment 

 the exact heating-power of the diflerent^woody species, and two 

 modes of measuring it have been devised, the former physical, 

 and the latter chemical. 



The physical method for measuring the heating-power of a 

 wood, consists in heating a boiler with the wood to be experi- 

 mented on, and ascertaining how many unit-weights of water at 

 0° C. can be changed into steam by a unit-weight of the 

 wood. 



The two elder Ilartigs have experimented in this manner with 

 equal volumes of wood, and have found, taking the heating 

 power of the stem of beech as 1 : — 



100 years old ashwood ..... 1*44 



120 ,, very resinous Scotch i)inc\v()t)d . 1"00 



Robinia (stem) 1*05 



100 years old hornbeam (stem) . . . . 1*05 



108 ,, sycamore (stem) . . . 1'03 



25 ,, beech-poles . . . . . 1*10 



