TIMBER; PHYSICS SOUTHERN PINK. 



349 



RELATION OF STRENGTH TO WEIGHT. 



The intimate relation of strength and specific weight lias "been well established by the experiments. The aver- 

 age results obtained in connection with the tests themselves were as follows: 



Transverse strength 



Specific weight of test pieces- 



Cuban. 



100 

 100 



Longleaf. 



91 

 94 



Loblolly. 



84 



82 



Shortleaf. 



77 

 77 



Since in the determination of the specific gravity above given, wood of the same per cent of moisture (as is the 

 case of the values of strength) was not always involved, and also since the test pieces, owing to size and shape, can 

 not perfectly represent the wood of the entire stem, the following results of a special inquiry into the weight of the 

 wood represents probably more accurately the weight and with it the strength-relations of the four species. 



WEIGHT RELATIONS. 

 [These data lefer to the average specific weight for all the wood of each tree, only trees of approximately the same age being involved.] 



Average a$e of trees 



Number of trees involved . . 

 Specific gravity ot dry wood 



Weight per cubic loot 



Kelative weight 



(Transverse strength a) 



Cuban. 



171 

 6 



0.63 

 39 

 100 

 (100) 



Longleaf. 



127 



22 

 0.61 



38 



97 

 (91) 



Loblolly. 



137 

 14 

 0.53 

 33 



84 

 (84) 



Shortleaf. 



131 

 10 



0.51 

 32 



81 

 (77) 



a The values of strength refer to all tests and therefore involve trees of wide range of age and consequently of quality, especially 

 those of longleaf, involve much wood of old trees, hence the relation of weight and strength appears less distinct. 



From these results, although slightly at variance, we are justified in concluding that Cuban and longleaf pine 

 are nearly alike in strength and weight and excel loblolly and shortleaf by about 20 per cent. Of these latter, 

 contrary to common belief, the loblolly is the heavier and stronger. 



The weakest material would differ from the average material in transverse strength by about 20 per cent and 

 in compression strength by about 30 to 35 per cent, except Cuban pine, for which the difference appears greater 

 in transverse and smaller in compression strength. It must, of course, not be overlooked that these figures are 

 obtained from full-grown trees of the virgin forest, that strength varies with physical conditions of the material 

 and that, therefore, an intelligent inspection of the stick is always necessary before applying the values in practice. 

 They can only represent the average conditions for a large amount of material. 



DISTRIBUTION OF WEIGHT AND STRENGTH THROUGHOUT THE TREE. 



In any one tree the wood is lighter and weaker as we pass from the base to the top. This is true of every tree 

 and of all four species. The decrease in weight and strength is most pronounced in the first 20 feet from the stump 

 and grows smaller upward. (See fig. 91.) 



This great difference in weight and strength between butt and top finds explanation in the relative width of 

 the summerwood. Since the specific weight of the dark summerwood band iu each ring is in thrifty growth from 

 .90 to 1.00, while that of the springwood is only about .40, the relative amount of summerwood furnishes altogether 

 the most delicate and accurate measure of these differences of weight as well as strength, and hence is the surest 

 criterion for ocular inspection of quality, especially since this relation is free from the disturbing influence of both 

 resin and moisture contents of the wood, so conspicuous in weight determinations. 



The following figures show the distribution of the summerwood in a single tree of longleaf pine, as an example 

 of this relation : 



In the 10 

 rings next 

 to the bark. 



I Per cent. 



At the stump 37 



32 feet from stump I 25 



87 feet from stump >. I 15 



In the 10 

 rings, Nos. 



100 to 110 

 from hark. 



Per cent 

 52 

 38 

 37 



Average 



ior entire 



disk. 



Pit cent. 

 50 

 33 

 26 



Specific 

 weight. 



0.73 

 59 

 55 



