Page:The Oak.djvu/158

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140
THE OAK.

how far the difference would hold if sufficiently numerous comparisons were made.

(5) Swelling may be regarded as complementary to shrinkage. It has been found that if oak wood is allowed to absorb water until thoroughly saturated it will increase from 0·13 to 0·4 per cent in length, and be distended radially from 2·66 to 3·9 per cent, or tangentially 5·59 to 7·55 per cent, according to age and condition, young wood swelling more than old. It has also been found that the total volume increased from 5·5 to 7·9 per cent, and the weight from 60 to 91 per cent, on complete saturation.

(6) Elasticity and Tenacity.—Oak is very elastic, and easily bent if steamed, and it does not readily splinter. When pulled in a direction parallel to the length of the structure the absolute tenacity = 2·23 to 14·51 kgr.—i.e., it took a pull equal to this weight per 1 sq. mm. of section to pull the wood asunder.

The limit of elasticity corresponds to a load of 2·72 to 3·5 kgr., according to various authorities, the specimen lengthening th in the former case.

The modulus of elasticity is given as 826 to 1,030 kgr., and the breaking limit as 4·66 to 6·85.

When the pull is in a direction across the length of the fibers, the results differ according as the load is applied so as to act radially or tangentially.

When acting radially the modulus of elasticity is given as 188·7 kgr., and the breaking limit as 0·582 kgr.

When acting parallel to a tangent the modulus of