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ELECTRICAL CONDUCTIVITY <br />Using Wheatstone Bridge <br />(Modified USDA Handbook 60) <br />STD Solution <br />Potassium Chloride O.O1N: <br />I, <br />Dry 1 $m of KC1 for one hour in oven <br />at 105 C, then weigh 0.7456 gm of dry <br />RC1 and dilute to 1 liter of deionized. <br />water. <br />Procedure for Analyzing Soil Samples <br />1. Fill centrifuge tube half full with O.O1N KC1 solution, <br />then record conductance of the solution with the cell <br />in open position and record temperature in °C to nearest <br />0.1°C. <br />2. Close the cell and fill with the same O.O1N KC1 solution <br />from centrifuge tube in step 1 and read conductance. <br />3. Rinse the cell with deionized water and shake water off <br />till dry. <br />4. Fill closed cell with sample and record the conductance. <br />Calculations <br />K = Cell Constant <br />K = Closed Cell Constant <br />c <br />ECt = Conductivity at the temperature of measurement <br />u mhos/cm <br />ECo = Conductivity of KC1 in Open Cell N mhos/cm <br />ECc = Conductivity of KC1 of Closed Cell u mhos/cm <br />ft = Temperature Factor from Table 15 of USDA <br />Handbook 60 <br />t = Temperature at Measurements <br />EC25 = Conductivity Corrected to 25°C <br />Kc = (ECo -ECc)K +K <br />(ECc)K <br />EC m mhos/cm = EC x f x l m mhos/cm <br />25 t t 1000 u mhos/cm x Kc <br />1, <br />1/ <br />6-43 <br />