132 OF WOOD IN GENERAL. 



in weight. Of the 429 species experimented upon the specific 

 gravity ranged from O2616 in the Small-fruited Fig (Ficus aurea) 

 to 1-3020 in Black Ironwood (Conddlia f fared). 



Bauschinger found, by experiments made at Munich in 1883 

 and 1887, that the density and strength of timber is greatly 

 affected by the amount of moisture it contains. To determine 

 the percentage of moisture Prof. Unwin gives this method. Drill 

 a hole through the test block and weigh the shavings at once. 

 Dry them in an oven at a temperature of from 200 to 212 F. for 

 8 or 10 hours, and, when they cease to lose weight, re-weigh 

 them. If then W = their first or wet weight, and D = their second 

 or dry weight, W - D = the weight of moisture they contain, and 



lOO(W-D) 



-^yr = the percentage of moisture. 



Bauschinger decided on 1 5 per cent, of moisture as the standard 

 dryness of air-dried wood. 



Ash percentage and fuel value. From the specific gravity 

 Mr. Sharpies deducted the percentage of ash (determined by 

 burning small dried blocks at a low temperature .in a muffle 

 furnace), in order to obtain the relative approximate fuel value. 

 This calculation is based on the assumption that the real value of 

 the combustible or volatile substance of all woods is the same. 

 Though resinous woods give off more than 1 2 per cent, more heat 

 on burning than do non-resinous woods, at least this amount is 

 lost in the case of the former in the form of uncorisumed carbon 

 in the smoke. The amount of heat obtained is, in fact, very 

 nearly in direct proportion to the specific gravity, i.e. the heavier 

 the wood the greater the amount of heat obtained. Taking as 

 the unit of fuel value an imaginary wood with no ash and a 

 specific gravity of 1, the relative fuel value of 430 woods examined 

 varied from 0-248 in Yucca to 1-194 in Black Ironwood (Conddlia 

 f fared). Taking as a unit of heat the amount necessary to raise 

 1 cubic decimetre or 1 kilogram of water 1 C., 4000 units will be 

 produced by burning a kilogram of dry wood, i.e. the relative fuel 

 value of any wood multiplied by 4000 will give approximately 

 the amount of heat obtained by burning a cubic decimetre of it. 



