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~~ ~r <br />Hot-Water Soluble <br />(ASA Agrcna~y No. 9, Methods of Soil Analysis) <br />Reagents <br />1. Ethyl Alcohol, 95$. <br />2. Curc:miin - Oral:ic acid reagent: <br />Dissolve 0.04 g curcaanin and 5 g oxilic acid in 100 ml of 95$ ethyl <br />alcokwl. Stable for 3 days when stored in refrigerator. <br />3. Calcium Hydroxide Suspension: <br />0.4 g Ca(OH)2 in 100 ml water. <br />4. Hydrochloric Acid: 2.5 N <br />5. Phenolphthalein: <br />.OS g phenolphthalein in 50 ml of 958 ethyl alcrohol and 50 ml of <br />water. <br />6. Barium Chloride (BaC12), 108 solution. <br />7. Stock Boron Solution: , <br />0.5716 boric acid diluted to 1 liter with water. 1 ml = 0.1 mg boron. <br />8. Standard Boron Solution: <br />10.0 ml of stock boron solution diluted to 1 liter with water. <br />1 ml = 1 ug boron. <br />9. All references to water in distiflled - deionized water. <br />Procedure <br />1. Place S..Og of soil in a 125 ml Erlenmeyer reflux flask and add 20 ml <br />water and 0.5 ml of 108 barium chloride solution. Prepare a blank in <br />the same manner, but delete sample. <br />2. Attach to reflux ocndensor. Heat to just sign of boiling and then reflux <br />for exactly 5 minutes. Allay to cool without removing the condensor.. <br />3. Decant the suspension into a 50 ml centrifuge tube and cPSitrifuge the <br />sUSpensiOn until clear. (Filtration may be necessary if samples remain <br />cloudy.) <br />4. 7Yansfer a 1 ml aliquot (or suitable aliquot to stay within the working <br />curve) into a 100 ml plastic beaker. ', <br />5. Prepare a calibration curve by pipeting .25 m1,..50 ml and .75 ml of <br />1 ug/ml standard solution into 100 ml beakers. Prepare a blank solution <br />ug/ml sra.+~ar.a solution into 100 ml beakers. Prepare a blank solution <br />for the standais7s. If sample contains < 40 ppm - NJ3, omit steps 6 S 7~ and <br />add 4.2 mis. of` Canc. HC1 to Curc~miin - Oxalic Acid reagent. <br />6-55 <br />