9·8 kgr., and the breaking limit 0·406 kgr.
The absolute tenacity in the transverse direction is given as 0·44 to 0·61 kgr.
In the case where pressures are applied in the direction of the length of the fibers the limit of elasticity = 2·09 to 2·22 kgr.; the modulus of elasticity, 933 to 1,250 kgr.; and the absolute resistance, 2·58 to 3·64 kgr.
Flexibility.—The limit of elasticity = 1·77 to 2·71 kgr.; modulus of elasticity, 620 to 735 kgr.; resistance to bending, 4·53 to 6·18 kgr.
Torsion.—Oak warps considerably unless carefully seasoned. Limit of elasticity = 0·4 to 0·54 kgr.; modulus of elasticity, 612·5 to 785 kgr.; resistance to torsion, 0·75 to 0·97 kgr.
Resistance to shearing-stress, in the direction of the fibers = 0·61 to 0·97 kgr.; perpendicular to them, 1·9 to 3·49 kgr.
(7) Resistance to Splitting.—Oak is easily split into tolerably smooth and even staves, and is much employed for this purpose.
(8) Hardness.—Oak is neither the hardest and heaviest nor the most supple and toughest of woods, but it combines in a useful manner the average of these qualities. Good oak is hard, firm, and compact, and with a glossy surface, and varies much; young oak is often tougher, more cross-grained, and harder to work than older wood. According to Gayer, if we call the resistance which the beech offers to the saw, applied transverse to the fibers, 1, then that of freshly felled oak = 1·09.
(9) Durability.—A mild climate and open situation produces the most durable oak, and it is extraordinarily durable under water, in the earth, or exposed to wind and weather, or under shelter; in the latter case it becomes more and more brittle as years roll by.
The alburnum becomes rotten usually in a few years if exposed, and is the prey of insects if under cover. The heart, if sound, may last for centuries under cover and well ventilated, and even in earth or water will endure for several generations. There are, for instance, in the museum at Kew, a portion of a pile from old London Bridge which was taken up in 1827, after having been in use for about 650 years, and a piece of a beam from the Tower of London, of which it is stated that it was "probably coeval with the building of the Tower by William Rufus"; and many other specimens of very old oak are known.
(10) Burning Properties.—The calorific power of oak wood is high, in accordance with its density, but it splutters and crackles and blackens too much. Nevertheless, it produces a valuable charcoal. Hartig says that if we call the cooking-power of a given volume of beech 1, that of an equal volume of oak = 0·92 to 0·96.
(11) Peculiarities.—Oak timber is apt to suffer from various diseases, and from frost-cracks and star-shakes, cup-shakes, etc., as we shall see in the next chapter. It often presents brittle wood, red-rot (foxiness), white-rot, spottiness of various kinds, and is sometimes twisted. At the roots it is very often affected with burrs. It contains gallic acid, and so corrodes iron nails, clamps, etc.
(13) Uses.—Owing to its high price and great specific weight, oak has suffered in competition with spruce, larch, and pine so far as building is concerned; but its uses are very various and widespread nevertheless, and it is invaluable to the engineer and builder wherever strength and durability are aimed at.
As already said, its great value depends on its marvelous combinations of several average properties; and considerable variations in the density, durability, ease of working, and beauty when worked, and so forth, are met with according to the situation and climate in which the oak grows. Generally speaking, it is found that when the oak grows isolated in plains, in rich soil and a mild climate (habitat of Q. pedunculata), it grows rapidly, and produces a wood of very tough and horny consistency, which is regarded as the best for naval and hydraulic work, cartwrights, etc., and wherever strength, tenacity, and solidity are required in high degree (Fig. 39, top). The best should have broad and equal rings, but not broader than 7 to 8 mm., with narrow vascular zone and the smal