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This 1 page Class Notes was uploaded by Rita Feil II on Tuesday September 8, 2015. The Class Notes belongs to SSC 220 at University of California - Davis taught by Randal Southard in Fall. Since its upload, it has received 43 views. For similar materials see /class/191781/ssc-220-university-of-california-davis in Soil Science at University of California - Davis.
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Date Created: 09/08/15
UCDavis SSC 220 Pedology CEC of the Clay and Fine Silt Fractions by Excess Salt Method Background Read Chapter 5 in Jackson and this procedure Objectives Measure CEC of the clay and fine silt fractions by the excess salt method Assess effects of pH on CEC Materials Airdry Nasaturated clay Airdry Nasaturated fine silt 220 pm 100 ml centrifuge tubes 100 ml volumetric asks with funnels Plastic bottles with screw top lids for displaced solutions 10 M CaClz 10 M MgClz 0005 M CaClz l M NaOAc pH 4 l M NaOAc pH 7 Ethanol EXCESS SALT METHOD 1 Preweigh centrifuge tubes to 00001 g labeled with a Sharpie directly on the tube no tape Weigh about 02000 g of clay or fine silt into tubes Prepare four samples of each clay and fine silt total eight tubes Weigh and record the weights of empty tubes and tubes plus clay or silt 2 To two tubes of each clay or silt add 20 ml pH 4 l MNaOAc and to the other two tubes of clay or silt add 20 ml pH 7 l M NaOAc Sonicate in ultrasonic bath for 2 minutes to mix Centrifuge at 2000 RPM for 10 minutes Decant supernatant into clear beakers to insure that no sample is lost Discard supernatant 3 Repeat washing with 20 ml lM NaOAc solutions disperse ultrasonic bath for 2 min stirring with glass rod but rinse stirring rod completely to avoid losing any sample centrifuge decant into beaker and measure pH with a pH meter until supernatant pH is that of the added buffer minimum of two washings but this may be all that is needed 4 Add 20 ml 10 M CaClz to each tube disperse with ultrasonic bath for 3 min stirring with glass rod Centrifuge at 2000 RPM for 10 min Discard supernatant 5 Wash disperse and centrifuge three times with 20 ml 0005 M CaClz Record the pH of the third wash We assume this brings the sample into equilibrium with the 0005 M CaClz Be careful that no sample is lost 6 Blot any large drops of solution in the tubes with KimWipes and immediately weigh tubes plus wet samples 00001 g Record weights 7 Add 20 ml 10 M MgClz to each tube Disperse carefully and thoroughly ultrasonic bath 3 min Centrifuge at 2000 RPM for 10 min
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