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PROCEDURE FOR DETERh1INATION OF <br />0.3 AND 15 ATMOSPHERE PRESSURE POINT <br />1. Preparatory Steps: <br />a. Sieve soil samples through a 8 mesh screen. <br />b. Pre-soak the porous plate for 2 hours inside the <br />pressure chamber. <br />2. Proceduso for setting un the pressure chamber: <br />a. Place the sample retainer rings on the porous plate. <br />b. Pour a soil sample into each rings, level with the top. <br />c. Allow the samples to stand at least 16 hours with <br />an excess of water on the plate. <br />3. At 8:00 a.m. the following dav: <br />a. Remove excess water from the membrane with a pipet <br />or rubber syringe. <br />b. Close the pressure membrane apparatus and admit air <br />to the soil chamber at a pressure of 1/3 atmosphere <br />• (5 p.s.i.). When running 15 atmosphere pressure <br />point apply a pressure of 15 atmosphere (220 p.s.i.). <br />c. Remove the samples when the readings on an outflow <br />buret indicate equilibrium has been attained. Some <br />soils will approach equilibrium in 18 to 20 hours. <br />d. Before releasing the air pressure in the pressure <br />cooker, put a pinch clamp on the outflow tube on <br />each plate. This prevents backflow of water to the <br />samples after the pressure is released. <br />e. To avoid changes in the moiiture content of the <br />samples, transfer the samples quickly to previously <br />weighed soild moisture cans. <br />f. Determine the moisture content by drying to constant <br />weight at 105°C. Express the moisture content as <br />percent, dry weight basis. <br />4. Calculate ~ moisture remaining after 1/3 atmosphere or 15 <br />atmosphere: <br />a. Subtract oven-dry weight of soil plus can from moisture <br />weight of soil nlus can. This gives weight of water <br />remaining after 15 atmosphere pressure. <br />b. Subtract weight of can from oven-dry weight of soil <br />plus can. <br />6-114 <br />