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 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,