14 



TIMBliK PINES OF THE SOUTHERN UNITED STATES. 



It is clear from the above diagnosis that Longleaf IMue may be distiuguished from Cuban Pme 

 by its liner grain and small amount of sapwood ; also that both of these differ from the Shortleaf 

 and Loblolly in their gieater weight and the more resinous character of their wood, but that the 

 wood of the two last-named species is rarely distinguishable beyond doubt. 



Technically the wood of the pines differs about as follows : The wood of the Longleaf and Cuban 

 pines are about equal in strength, Longleaf excelling by its finer grain and smaller amount of 

 sapwood. The same comparison may be made with regard to Loblolly and Shortleaf Pine. Being 

 much more variable, however, in weight and grain, exceptions to the general rule here are very 

 numerous. Of the last-named species it may be said that the wood derived from more southern 

 localities is generally heavier and stronger than northern grown — a fact especially apparent in 

 the case of the Shortleaf Pine. 



The extensive investigations carried on l)y the Division of Forestry during the last three to 

 four years mainly on these pines permit us to give the following rusumc^ of their mechanical 

 properties derived from not less than 20,000 tests and as many measurements and weighings. 

 We quote this information Irom Circular 12 of the division : 



JIECHANIOAL PROl'EUTIES. 



In general the wood of all these pines is heavy for pine (31 to -10 pounds per cubic foot, when 

 dry), soft to moderately hard (hard for pine), requiring about 1,000 pounds per square inch to indent 

 one-twentieth inch; stiff', the modulus of elasticity being from 1,500,000 upward; strong, requiring 

 from 7,000 pounds per square inch and upward to break in bending and over 5,000 pounds in 

 compression when yard-dry. 



The values here given are averages based on a large number of tests fiom which only defective 

 pieces are excluded. 



In all cases where the contrary is not stated the weight of the wood refers to kiln-dried 

 material and the strength to wood containing 15 per cent moisture, which may be conceived as 

 just on the border of air-dried condition. The first table gives fairly well the range of strength of 

 commercial timber. 



Jverage sireiigih of Southern Pine. 

 [Air-dry material (about 15 per cent moisture).] 



RELATION OF STRENGTH TO WEIGHT. 



The intimate relation of strength and specific weight has been well established by the experl- 

 lents. The average results obtained in connection with the tests themselves were as follows: 



