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. 524 AIR-TO-WATER PERMEABILITY RATIO i 41-3 PERMEABILITY OF SOIL TO AIR 525 <br /> the concentration and composition of salts in the water greatly influence in length to the air outflow tube. This apparatus is shown diagram- <br /> the water permeability. The concentration effect alone has been observed matically in Fig.41-1. <br /> to cause changes in permeability as great as several hundredfold. This is 3. Soil container: Punch a hole of diameter >_ 5/32 inch in the bottom of <br /> particularly true where soils having high exchangeable sodium are involvedY. I a 13/4-inch-diameter tinned-iron can (size designation = 3 ounce) with <br /> The quality of the water to be used will depend upon the purpose of the s the flare of the hole outward. In the bottom of the can, place first a <br /> test.In general,it may be stated that the quality of the water should coincide disc of brass screen, with 20 to 40 meshes per inch, and then one or <br /> with that of the water to which the soil is subjected in the field. If the sta- ; more layers of fiberglass sheet as a support and filter. In the center of <br /> bility of soil structure under rainfall conditions is being investigated, then i the lid that fits the can, bore a hole of diameter > 1/2 inch. Solder a <br /> demineralized or distilled water would be appropriate. If the effect of irri- r short length of brass or copper tubing (diameter > 1/2 inch) into the <br /> gation on the physical condition of soils is being studied, then a water of the central hole in the lid. Make a top extension for the can from a 4-cm. <br /> composition and concentration of the irrigation water should be used. In section of brass tubing 2i/4-inch in diameter by 0.042-inch wall thick- <br /> any case,the concentration and composition of the water are very important ness, counterbored on the lower inside to allow it to fit snugly on the <br /> considerations and should be reported along with the water permeability top of the can. <br /> data. <br /> For additional information, the papers of Reeve (1953), Reeve and <br /> Brooks (1953), U. S. Salinity Laboratory Staff (Handbook 60) (1954), 41-3.2 Procedure <br /> Kirkham (1947), and Brooks and Reeve (1959) should be consulted. <br /> Pass air-dried soil through awire-mesh sieve with 1-mm. openings. Ob- <br /> tain a representative sample by quartering or by taking at random a large <br /> 41-3 METHOD FOR PERMEABILITY OF SOIL TO AIR 2 number of small scoopsful from the soil pile. As indicated in Fig. 41-2, <br /> part 1, place brass cylinder extension B on top of can A, and fill the con- <br /> tainer thus formed about three-fourths full of soil. To reduce segregation, <br /> dump in the soil rather than pouring it in or scooping it in. Pack the soil <br /> 1. Compressed-air source. in the container by dropping the soil-filled container from a height of 2.5 <br /> 2. Air-storage tank: Fit a 213-liter air tank (55-gallon drum) with a valve cm. 200 times on a solid wooden block. Remove the brass cylinder exten- <br /> and inlet tube from a compressed-air supply and with an outflow tube sion from the can, and use a spatula to strike the soil off level with the top <br /> with a full opening control valve (diameter >_ t/2 inch) for discharging of the can. As indicated in Fig. 41-2, part 2, cover the soil with a disk of <br /> air through the soil sample. Connect a water manometer about 100 cm. filter paper, place the lid with the metal-tubing air connection C on the can, <br /> 'Reeve (1953),after Kirkham (1947). complete the seal of the lid to the can with a tight, broad rubber band or <br /> with a mixture of 50% paraffin and 50% beeswax. <br /> COMPRESSED AIR STORAGE WATER SOIL Admit compressed air to the tank until a manometer displacement y„ is <br /> AIR SUPPLY TANK MANOMETER SAMPLE attained (y„ = 30 cm. is a convenient value). Record the temperature of <br /> the air in the tank and the barometric pressure of the atmosphere. Open <br /> the outflow valve to allow air to flow from the tank through the soil sample, <br /> —' and record the time in seconds and the manometer level in centimeters at <br /> approximately 2-cm.intervals from about yl = 20 to y:, = 10. <br /> CONSTANT <br /> i <br /> y2 <br /> VOLUME -- <br /> 41-3.3 Calculations <br /> Calculate the permeability of the soil using air by the equation <br /> U-- k,a _ 2.30LVS,1 [12] <br /> Fig.41-1. Non-steady-state method for air permeability (After Kirkham, 1947). AP„ <br />