n 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 smallest possible vessels, and with a pale, rather than dark, and even color on the fresh section. It should also have long fibers and a strong, fresh smell.In close, high forest, on poor soil, and in a rougher climate, it may take 300 years to reach 0·6 metre diameter, and the wood is then softer and more porous,
Fig. 39.—Three specimens of oak grown under different conditions.
beautifully speckled, and shrinking little (Fig. 39, middle). Such wood is excellent for sculpture and carving, and is very pretty; it is also well adapted for cooperage.
In deep soil of moderate quality, in hilly country, and growing as coppice under standards, we have a wood of irregular growth and not very valuable, but useful in an all-round way for sawing and splitting (Fig. 39, bottom).
Speaking generally, it is found that, other things being equal, the most resistant, closest, and toughest timber comes from isolated trees growing in the open: straight and long timber, less marked for the above qualities, comes, on the contrary, from trees grown in close, high forest. This is the conclusion arrived at by the naval authorities in France and England, and may be accepted as according with the facts of structure, etc. Some differences may be put down to the varieties, but probably Boppe is right in concluding that rate of growth, etc., due to differences in the soil and climate, are the determining causes.
The builder employs oak for sills, staircase treads,
Description of Fig. 39.—The upper one is from a rapidly-grown tree, in the open, and at a low altitude; the wood is very strong, hard, and heavy (density 0·827), because there is a preponderance of fibers in the broad rings. The middle specimen comes from a tree growing slowly in a forest at a considerable altitude; the narrow rings have too large a proportion of vessels, whence the wood is soft (density 0·691), porous, and weak. The lower section is from a tree which has grown very irregularly on poor soil, as shown by the variable rings; only the parts with broad rings are good—hence 