Engineering and Contracting . easily transported and at a freight cost far less thanthat of the heavy horizontal-cylinder equipment. THE DAVIS SPOT TEST IN THE PRELIMINARYEXAMINATION OF CREOSOTE OILS. The presence of tar, free carbon or dirt in creosote oilis indicated in very minute quantities in the by the use of the Davis spot test. This test,while very simple, has proved certain and unfailing. Itis as follows: Allow six drops of a sample of creosote oil to fall uponthe surface of clean, white blotting paper. If tar, freecarbon or dirt is present it will be readily*
Engineering and Contracting . easily transported and at a freight cost far less thanthat of the heavy horizontal-cylinder equipment. THE DAVIS SPOT TEST IN THE PRELIMINARYEXAMINATION OF CREOSOTE OILS. The presence of tar, free carbon or dirt in creosote oilis indicated in very minute quantities in the by the use of the Davis spot test. This test,while very simple, has proved certain and unfailing. Itis as follows: Allow six drops of a sample of creosote oil to fall uponthe surface of clean, white blotting paper. If tar, freecarbon or dirt is present it will be readily* observed, asit quickly segregates at the center. The paper shouldbe laid away in a flat position for a few hours in a placewhere there is no dust. If then examined, foreign matterwill be observed in a distinct zone in the center of thespot, the outer zone very readily indicating the characterof the oil. The various types of wood-preserving oils can be easilydistinguished from each other by this test when they aretrue View of Vertical Tank Creosoting Plant at Orrville, O. shown is at Orrville, Ohio, where the Shipley process ofcreosoting is used. The cylinders are made in two sizes,one designed for containing .300 yd. of paving blocks andthe other for 200 yd. Each is fitted on the inside with ahydraulic plunger and platform, so that when empty andabout to be charged with wood blocks, the platform isat the top. As the blocks are delivered into the tank,the platform lowers gradually, thus preventing the cylinder is full, the cover is put on and theusual treatment administered. Then the cover is taken In order to determine the sensitiveness of the spot ordiscoloration test and to make it fairly quantitative, aseries of spots was made by the Forest Products Labora-tory at Madison, Wis., from a carbon-free creosote oil towhich carbon in the form of lampblack had been addedin graduated amounts. The results obtained disclosed anincreasing gradation of the free c
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