142 THE OAK 



transverse to the fibres, 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 hav- 

 ing 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. Never- 

 theless, 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, &c., as we shall see in the next chapter. It 

 often presents brittle wood, red-rot (foxiness), white-rot, 



