PHILIPPINE FIREWOOD. 11 



the weight of carbonate as ash. Perhaps iron originally in the ferrous condition 

 is oxidized to the ferric. All these things make the ash content high. On the 

 other hand, there may be water which can not be expelled by drying at 105° 

 and is still not retained as ash. Wood minus water and ash may be one thing 

 for one wood and another for another. When the per cent of ash is large the 

 error may be of considerable magnitude; I can not offer a method for the calcula- 

 tion of the amount. The uniformity in the calorifie value of that part of the 

 wood remaining after deducting the water and the ash might be increased were it 

 possible to determine the extraneous mineral matter in the wood instead of that 

 remaining after combustion. 



The relation of the relative weight of wood to its everyday use is 

 extremely important. The density is at the basis of its consumption in 

 almost every enterprise. As wood for fuel is sold by measure, a knowl- 

 edge of the relative weight is especially important. 



This property is sometimes expressed in terms of cubic meters, but usually by 

 specific gravity. The weight of any quantity of wood can be computed from 

 these data. In general one thinks of the density of the wood fiber with its resin, 

 coloring material, etc., as synonymous with specific gravity, but one can see at 

 once that the wood cells sometimes contain a certain amount of air; and that 

 the amount of air or water in the interstices might have a great deal to do with 

 the latter. Bauschinger ^'' has shown the relation between the specific gravity 

 and the pei'centage of moisture. "At first the specific gravity diminishes rapidly 

 as the percentage of moisture is reduced, but when this has been reduced to 15 

 per cent the specific gravity changes very little for any further xeduction in 

 moisture. This shows that the shrinkage is insignificant until the timber becomes 

 nearly dry, when it swells and shrinks almost directly with the percentage of 

 moisture, so that the weight of a unit volume, which is a measure of the specific 

 gravity, remains nearly constant." 



Therefore it will be seen that the porosity or compactness of an air- 

 dried wood with its respective amount of resin, coloring material, etc., is 

 a direct function of its specific gravity and a variation of a few per cent 

 in the water content within the above-named limits has no influence. 

 The specific gravity of mineral matter is from 2.5 to 3.5, and therefore 

 liigh ash would exert an influence on the specific gravity, but the per- 

 centage of ash in wood is usually so small as to be in general of little 

 consequence. 



There is no entirely satisfactoiy method of determining the volume 

 of porous bodies like wood, but some means of immersion is unquestion- 

 ably the best. I at first thought of using mercury, but this was given 

 up because of the great difference in specific gravity between the mercury 

 and the wood and furthermore because the hanging bubbles of air could 

 not easily be seen. My method was as follows : 



I used a cross section of the wood of the proper length and split from 2 to 4 

 pencil-shaped pieces from dilTerent parts so large that they would just enter a 

 large-mouthed specific gravity bottle. The weight of the bottle with water at a 



"Femow, B. E., Timber Physics, Pt. 1, U. S. Dept. Agr., For. Div. Bull 6, 

 40; Report of Tests made at the Govt. Testing Laboratory at Munich 16. 



