PHILIPPINE FIREWOOD. 



13 



It will be seen that the calorific values of Philippine woods vary but 

 little, not so much as would be anticipated from the presence of varying 

 quantities of complex gums, resins and color substances. I have given 

 the average heating value of the combustible matter of wood, wood — 

 (water-f-ash), as 4,418 calories. The available heating value of any wood 

 can be calculated approximately by first reducing the above value in 

 proportion to the diluents, water and ash, and then subtracting a number 

 of calories equal to 6 times the per cent of water in the sample, i. e.. 



Calories = 4418 X (— 



(per cent water + per cent ash)\ 

 100 ' 



■6X per cent water. 



Aside from the percentage of water and ash, the chief factors controll- 

 ing the selection of a firewood are physical, i. e., compactness or weight, 

 as indicated by the specific gravity. 



The fiber of all woods when finely powdered and completely dried has 

 approximately a constant specific gravity of about 1.5. This shows that 

 the weight of ordinary wood depends mairdy upon two things — its com- 

 pactness and its moisture, that the amoimt of woody fiber in woods con- 

 taining the same amount of moisture is approximately proportional to 

 the specific gravity, and that usually the best firewoods are those with 

 very dense cell walls. Therefore, the fuel value of wood may be roughly 

 classified on this basis as shown by the following tables of common North 

 American woods ^'' and of some of the Philippine firewoods. 



Table VIII. — Approximate fuel value of North American woods. 



Fuel value. 



Kind of wood. 



Specific 

 gravity. 



Reference. 



Poor (sp. gr., 0.25 

 to 0.45). 



Cypress: 



Bald cypress {Taxodiuin distichum Rich.), 

 Fir: 



Balsam fir (Abies balsamea Mill.) 



0.454 



0.382 

 0.354 

 0.423 

 0.456 

 0.470 

 0.424 

 0.518 



0.316 

 0.379 



0.332 

 0.462 

 0.402 

 0.421 

 0.288 

 Boston 



Penhallow, «p. 217. 



Penhallow, p. 258. 

 Penhallow, p. 261. 

 Penhallow, p. 260. 

 Penhallow, p. 262. 

 Penhallow, p. 259. 

 Penhallow, p. 266. 

 Penhallow, p. 270. 



Penhallow, p. 221. 

 Penhallow, p. 221. 



Penhallow, p. 231. 

 Penhallow, p. 232. 

 Penhallow, p. 219. 

 Penhallow, p. 224. 

 Penhallow, p. 225. 

 (1907). 



White fir [A. grandis Lindl.) 



White fir (A. amabilis Forbes) 



Red fir {A. nobilis Lindl.) 



Red fir {A. magnijica A. IMurr.) _ 



Hemlock (Tsuga canadensis Cslvt.) 



Hemlock ( T. mertensiana Carr.) _ 



White cedar: 



White cedar {Thuya occidentalis Linn.).__ 

 Canoe cedar (T. gigantea Nutt.) 



White cedar ( Chamaecyparis tliyoid.es 

 (Linn.) B. S. P.) .- . ... 



White cedar (C. lawsoniana A. Murr.) 



White cedar (Libocedrus decurrens Torr.). 

 Redwood (Sequoia sempervirens Endl.) ... 

 Big tree (S. (72(7an(ea Decne.). 



« Penhal 



ow, D. P., North American Gymnosperms 



"The list of common woods was largely taken from U. S. Dept. Agr., Biv. For. 

 Bull. (1895), No. 10, 72. 



