7.166
7,813
7,575



The amount of resin in the wood varies greatly, and trees growing side by side differ within very wide limits.
Sapwood contains but little resin (1 to 4 per cent), even in those trees in which the heartwood contains abundance.
In the heartwood the resin forms from 5 to 24 i>er cent of the dry weight (of which about one-sixth is turpentine and
can not be removed by bleeding), so that its (]uantity remains unaffected by the process. Bled timber, then, is as
useful for all purposes as unblod.
To give au idea how necessary it is that a large series of material be tested before making
statements of the strength of wood of any species, we reproduce one of the many tables contained
in Bulletin 8, which at the same time exhibits the variation of strength throughout the tree aud
from tree to tree.
TTMBKK PHYSICS SOUTHERN PINE.
357





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