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O%'~ANIC MATTER <br />(Modified USDA Handbook 60) ' <br />• Sol'n A - Potassium dichromate, 1.00 N. Dissolve 49.090 gm of potassium <br />dichormate in 1 litre of deionized water. (Use analytical balance.) <br />Sol'n B - Sulfuric acid silver sulfate, dissolve 30 gm of silver sulfate in a <br />5 pt. bottle of concentrated sulfuric acid. <br />Sol'n C - Fermin Indicator <br />Sol'n D - Ferrous sulfate, 1 N. Dissolve 280 gm of FeSO •7H2O in 800 cols of <br />deio~nized H 0, add 30 ml of concentrated sulfu~ic acid, dilute to a <br />litre and s~daxtiize daily. <br />Procedure <br />1. Weigh 1 gm of soil into a 250 ml Erlenmeyer flask. <br />2. Add 10 ml of Sol'n A to each flask including your standards and <br />blank. <br />3. In the hood, add 20 cols of Sol'n B to every flask, if the sol'n <br />turns green, add additional Sol'n A and record amount cf excess <br />Sol'n A that is required. <br />• 4. Preheat hot plate on High for 10 minutes. <br />5. Heat samples and blanks on hot plate to 150°C in a heating period <br />of 1 minute (keep the solution moving while heating). <br />6. Allan to cool in hood, then add deionized H2O to attain a wlume <br />of 150 cols. <br />7. Add one squirt or 10 drop of Fermin indicator to every flask. <br />8. Titrate with Sol'n D until color changes from green to red, and <br />reooxd wlume of Sol'n D used to two decimal places. <br />Calculations <br />N FL=SO4 = 1.00 N K2Cr2O7 x 10 ml <br />D <br />Where D is nunber of cols of Sol'n D required for color change in <br />gtant3arr~e, <br />8 OM = [(cols of sol'n A x 1.00 N IC2Cr2O7) - (cols of sol'n D x N FeSO4)] x .578 <br />• 1 gr sample <br />Calculate 9 OM of BK before calculating samples. <br />Diy Basis $ OM = Qy <br />Dry Weight of Sample <br />6-50 <br />