SECT. X.]
NATURE AND PROPERTIES OF TIMBER.
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of vessels. For joiners’ work it is also much used, both for external and internal work, asit is more easily wrought, stands better, is nearly if not quite as durable, and is muchcheaper than oak.
The colour of the wood of the different varieties of Scotch fir differs considerably • itis generally of a reddish yellow, or a honey yellow, of various degrees of brightness. Itconsists in the section of alternate hard and soft circles; the one part of each annual ringbeing soft and light coloured, the other harder and dark coloured. It has no larger trans-verse septa, and it has a strong resinous odour and taste. It works easily when it does notabound in resin; and the foreign wood shrinks about one-thirtieth part of its width in sea-soning from the log.
In the best timber the annual rings are thin, not exceeding one-tenth of an inch inthickness; the dark parts of the rings of a bright and reddish colour; the wood hard anddry to the feel, neither leaving a woolly surface after the saw, nor filling its teeth with resin.The best Norway is the finest of this kind, and the best Riga is of similar quality, andmuch used for masts. Memel is stiffer, and in other respects not much inferior.
The inferior kinds have thick annual rings; in some kinds the dark parts of the ringsare of a honey yellow, the wood heavy, and filled with soft resinous matter, feels clammy,and chokes the saw. Timber of this kind is not durable, nor fit for bearing strains. MarForest timber is often of this kind. In other inferior kinds the wood is spongy, containsless resinous matter, and presents a woolly surface after the saw. Swedish timber is oftenof this kind, and is then inferior in strength and stiffness.
The cohesive force of a square inch of foreign timber varies from 7000 to 14000 pounds.
of Mar Forest . 7000 to 10000
• of English growth . 5000 to 7000
The weight of a cubic foot of foreign fir seasoned, varies from 29 to 40 lbs.
of English growth, seasoned.28 to 33
pf Mar Forest..38
The mean weight of the modulus of elasticity for a square inch
of the foreign varieties of Scotch fir of a good quality is 1,687,000 pounds.
The mean strength, stiffness, and toughness of oak, being each represented by KK’bthose of the different varieties of Scotch fir will be represented by the numbersbelow:
Strength of foreign timber 80, of Mar Forest ditto 61, of English grown ditto 60
Stiffness.114,.49,. .. 55
Toughness. 56,. 76,. 65
Mr. John White favoured the author with a specimen of Norway yellow fir much supe-