Forest Mensuration 13 



water. In the metric system, it equals weight in kilograms over cube- 

 decimeters of volume. The specific gravity is found by weighing a given 

 body, and then weighing it again immersed in water. It equals weight 

 outside water over loss of weight submerged in water. The division of 

 the metric weight of a large body by the specfic gravity of a sample piece 

 yields the volume of the body in cubic decimeters. 



Since wood is lighter than water, usually, a piece of lead must be 

 attached to the wood in order to submerge it. There must be ascer- 

 tained : 



1. The absolute weight of the piece of lead, H; 



2. The weight of the same piece submerged in water, h; 



3. The absolute weight of the wood and of the lead, G; 



4. The weight of wood and lead submerged in water, g. 



The weight of the wood alone is, consequently, (G H). 

 The specific gravity of the wood is 



G H 



The volume, in cubic feet, of a quantity of wood weighing n pounds, 

 and having the specific gravity s, is 



n 1 16n 



volume = X = 



s 63 1000s 



The figure 63 represents the weight in pounds of one cubic foot of 

 water. 



The specific gravity of wood is greatest close to the stump and in the 

 branches. For some species the outer layers show the greatest specific 

 gravity; for others the inner layers. 



Rules to convert specific gravity into weight per 1,000 feet board 

 measure or into weight per cord read as follows : 



1. Multiply specific gravity by 5,200. The result is the weight of 

 lumber per 1,000 feet board measure in pounds. 



2. Multiply specific gravity by percentage of solid wood contained in 

 a stacked pile; then multiply the product by 8,050. The result gives the 

 weight per cord in pounds. 



