. Bulletin. Forests and forestry -- United States. SEASONING WOOD. 31 and if left many months all pieces sink. Yet even after a year's immer- sion a piece of oak 2 by 2 inches and only C inches long still contains air, i. e., it has not taken up all the water it can. By rafting, or pro- longed immersion, wood loses some of its weight, soluble materials being leached out, but it is not impaired either as fuel or as building material. Immersion and, still more, boiling and steaming reduce the hygroscopicity of wood and, therefore, also the troublesome "working" or shrinking and swellin
. Bulletin. Forests and forestry -- United States. SEASONING WOOD. 31 and if left many months all pieces sink. Yet even after a year's immer- sion a piece of oak 2 by 2 inches and only C inches long still contains air, i. e., it has not taken up all the water it can. By rafting, or pro- longed immersion, wood loses some of its weight, soluble materials being leached out, but it is not impaired either as fuel or as building material. Immersion and, still more, boiling and steaming reduce the hygroscopicity of wood and, therefore, also the troublesome "working" or shrinking and swelling. Exposure in dry air to a temperature of 300° F. for a short time reduces, but does not destroy, the hygroscopicity and with it the tend- ency to shrink and swell. A piece of red oak, which has been sub- jected to a temperature of over 300° F., still swells in hot water and shrinks in the kiln. In artificial drying, temperatures of from 158° F. to 180° F. are usually employed. Pine, spruce, cypress, cedar, etc., are dried fresh from the saw, allowing four days for 1-inch boards; hard woods, espe- cially oak, ash, maple, birch, sycamore, etc., are air-seasoned for three to six months, to allow the first shrinkage to take place more gradually, and are then exposed to the above temperatures in the kiln for about six to ten days for 1-inch lumber. Freshly cut poplar and cotton wood are often dried directly in kilns. By employing lower temperatures, 100° to 120° F., green oak, ash, etc., can be seasoned in dry kilns without danger to the material. Steaming the lumber is commonly resorted to in order to prevent check- ing and "casehardeuing," but not, as has frequently been asserted, to enable the board to dry. Yard-dried lumber is not dry, and its moist- ure is too unevenly distributed to insure good behavior after manufac- ture. Careful piling of the lumber, both in the yard and kiln, is essen- tial to good drying. Piling boards on edge or standing them on end is
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