THE USES OF WOOD. 225 



In practice, several methods of sawing are used to bring 

 out the silver grain. The most common is to quarter 

 the logs, and then saw each quarter, as shown by the 

 lines in Figure 69. 



Ft'EL V.\LTTE OF AVOOPS.* 



" The Relative Fuel Values here given are obtained 

 by deducting the percentage of ash from the specific 

 gravity, and are based on the hypothesis that the real 

 value of the combustible material in all woods is the 

 same. 



"It appears from Mr. Sharpies' experiments that resin- 

 ous woods give upwards of twelve per cent, more heat 

 from equal weights burned than non-resinous woods; 

 the heat produced by burning a kilogram of dry non- 

 resinous wood being about 4,000 units, while the heat 

 produced by burning a kilogram of dry resinous wood 

 is about 4,500 units, a unit being the quantity of heat 

 required to raise one kilogram of water one degree centi- 

 grade. 



"Count Rumford first propounded the theory that the 

 value of equal weights of wood for fuel was the same, 

 without reference to specific distinctions; that is, that a 

 pound of wood, whatever the variety, would always 

 produce the same amount of heat. Marcus Bull, experi- 

 menting in 1826 upon the fuel value of different woods, 

 foimd a variation of onlyeleven per cent, between the 

 different species tested. Rumford's theory must be re- 

 garded as nearly correct, if woods are separated into 

 resinous and non-resinous classes. The specific gravity 

 gives a direct means of comparing heat values of equal 

 volumes of wood of different resinous and non-resinous 



* This .trtifle on the fuel value of woods is taken from the "Report 

 ^1 the Tenth Census," by Prof. C. S. Sargent. 



