. Wood; a manual of the natural history and industrial applications of the timbers of commerce. Wood; Timber. 70 OF WOOD IN GENERAL to first steam the timber, wMch. reduces its hygroscopicity and, therefore, its warping. This, however, is said to reduce the strength, if not also the durability, of the wood. If not steamed, the ends of boards should be clamped before kiln-drying to prevent splitting and warping. Neither hygroscopicity nor shrinkage of wood can be altogether overcome by drying at temperatures below 200° P. ; but as a rule only the first shrinking is hkely to cause splitting, so
. Wood; a manual of the natural history and industrial applications of the timbers of commerce. Wood; Timber. 70 OF WOOD IN GENERAL to first steam the timber, wMch. reduces its hygroscopicity and, therefore, its warping. This, however, is said to reduce the strength, if not also the durability, of the wood. If not steamed, the ends of boards should be clamped before kiln-drying to prevent splitting and warping. Neither hygroscopicity nor shrinkage of wood can be altogether overcome by drying at temperatures below 200° P. ; but as a rule only the first shrinking is hkely to cause splitting, so that any timber which has had from three to six months' air-drying may be safely kiln-dried. Too rapid kiln-drying, however, is apt to produce " case-hardening " in Oak and other hard woods, the drying and shrinking, that is, of an outside sheU followed by " honey- combing," or sphtting of the interior along the pith-rays (Fig. 43). Previous air-drying or steaming will obviate this. Various tem- peratures are employed in kiln-drying; but it is stated that at 100° to 120° F., Oak, Ash, and other hardwoods can be seasoned in dry kilns without any of the loss of strength often alleged to result from artificial heat. Poplar planks are dried in kilns in America at 158° P. to 180° P.; but Oak, Ash, Maple, Birch, Sycamore, etc.,. Fig. 43-—" Honeycombed " tooard, splitting along the pith-rays. (After Roth ) are first air-seasoned for three to six months, and are then exposed to these temperatures for six to ten days for 1-inch stuff. Pine, Spruce, Cypress, and Cedar of the same dimensions are dried for four days immediately after being felled and sawn up. Such temperatures are more than sufficient to kill and prevent fungus growth, and the fact that well-ventilated seasoned wood is seldom attacked shows that the amount of moisture then left in the wood is insufficient to support fungus growth. Walnut gun-stocks are desiccated in the rough by a curre
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