114 OF WOOD m GENERAL 



volume wiU= ~ cubic feet ; and if W= its weight in pounds, the 

 1728 



1728W , 

 heaviness of the wood per cubic foot mll= ~^^ ^^s- 



In the second method, if W=the weight of the block in pounds, 

 W'=the weight in pounds of the water it displaces, and G=the 

 weight of a cubic foot of water, Le, 62-4 lbs. at the normal tempera- 



ture, then ^=the volume of the block in cubic feet, and the 



heaviness of the wood per cubic foot will be -^. 



Mr. Stephen P. Sharpies, who made the examinations of North 

 American timbers incorporated by Professor Sargent in the Ninth 

 Census of the United States, vol. ix. (1880), making at least two 

 determinations for each species, calculated the specific gravity by 

 measurement with micrometer cahpers and weighing. The specie 

 mens tested were 100 millimetres long and about 35 millimetres 

 square, and were dried at 100" C. until they ceased to lose in weight. 

 Of the 429 species experimented upon the specific gravity ranged 

 from 0-2616 in the Small-fruited Fig {Ficus aurea) to 1-3020 in 

 Black Ironwood {Gonddlia ferrea), 



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, the strength falling very 



rapidly in any one quality of timber as the percentage of moisture 



increases. To determine the percentage of moisture Professor 



TJnwin 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° P. 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 



, lOO(W-D) , , . 



they contain, and ^r =the percentage of moisture. 



The maximum of strength is reached, not when the timber is 

 perfectly dry, but when there is from 3 to 4 per cent, of moisture 

 in it. 



Bauschinger decided on 15 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 



