UNIV. OF MICH. Issued July 2, 1907. U. S. DEPARTMENT OF AGRICULTURE, FOREST SERVICE-Circular 101. GIFFORD PINCHOT, Forester. THE OPEN-TANK METHOD FOR THE By CARL G. CRAWFORD, CHIEF, OFFICE OF WOOD PRESERVATION. GOVERNMENT PRINTING OFFICE: WASHINGTON: 1907 species this method is practicable in cases where no other process could be employed, and that its general application will make possible the treatment of much larger quantities of timber in the future than in the past. For those cases to which it is properly applicable, the saving effected by the open-tank method is readily apparent. Not only is the cost of operation and maintenance comparatively slight, but the cost of installation is probably less than one-fourth of that of a pressure-cylinder plant of the same daily capacity. Moreover, the open-tank apparatus may be moved with comparative ease, so that it may more nearly follow the base of supply, with a consequent saving of freight charges. It should be distinctly borne in mind that it is not a universal substitute for the pressure processes, and its future usefulness will largely depend upon the care and foresight which are exercised in its application. NECESSARY APPARATUS. The simplest type of open-tank apparatus consists of a vat to be partly filled with a preservative, in which the timber is submerged, and under which a fire can be built. An apparatus of this kind may be placed on wheels and drawn from one place to another. However, where the saving of time is essential and the treatment is conducted on a larger scale, additional apparatus is necessary for the most economical and convenient treatment. If the timbers are of such size and form that it is practicable to change them from the hot to the cold bath, two tanks are necessary, one to contain the hot preservative-preferably equipped with steam coils-and the other to contain the cold preservative. For timbers too large to be transferred during treatment, the plant should consist of a treating tank, a supply tank, and a receiving tank. This equipment will make it possible to shorten the treatment by running out the hot liquid into the receiving tank and admitting the cold liquid simultaneously. The preservative can later be pumped back into the supply tank. In most cases a tank built from three-sixteenths or one-fourth inch iron or steel will give the best results. Where steam can be supplied at a nominal cost, steam coils are preferable for heating. Approved: JAMES WILSON, Secretary. WASHINGTON, D. C., April 30, 1907. [Cir. 101] |