Cores 11 through 26 by Gary B. Dr - University of Illinois at Urbana ...

plastic, wide-mouth, screw-cap bottle. Ten mL of a 10% solution of sodium hexametaphosphate (NaPO 3) 6was added to the bottle followed by 140 mL of deionized water. The blank contained (NaPO 3) 6anddeionized water only. All bottles were sealed and placed on an oscillating shaker and shaken at 120 strokesper minute overnight. After shaking, 250 mL of deionized water was added to each bottle. The bottleswere then shaken end-to-end by hand for 25 seconds to dislodge settled sand and silt, then end-over-endfor 15 seconds. At the end of the 15-second period, the bottles were immediately placed in a covered,static water bath at 25C for 3 hours and 36 minutes to allow particles larger than 2 µm to settle from thetop 5 cm of the suspension. The shaken samples were placed in the water bath at two-minute intervals toprovide ample time between samples to withdraw aliquots for further processing. At the end of the settlingperiod, the bottles were removed from the water bath at two-minute intervals in the same sequence inwhich they were placed into it. The tip of an Oxford® Macro-Set adjustable pipet was carefully insertedinto the suspension to a depth of 5 cm, and exactly 10 mL of the suspension was withdrawn during a 15-to 20-second period. The pipet had been previously calibrated by weighing and averaging 10 replicatevolumes of deionized water at the desired volume. The suspension was delivered to a numbered, weighedaluminum weighing pan. When aliquots of all the samples and the blank had been delivered to theirrespective weighing pans, the pans were placed in an oven to dry overnight at 110C.After the aliquots of suspended clay fraction had been withdrawn, the contents of each bottle were pouredthrough a 3.5-inch diameter, 62 m (No. 230) stainless steel sieve to separate the sand-size particlesfrom the silt- and clay-size particles. Each bottle was thoroughly rinsed with deionized water. Successiverinsates were poured through the sieve until no particulate matter could be observed in the bottle. The sandwas rinsed several times to remove all silt-size and smaller particles.The sand was then backwashed from the sieve with deionized water into a beaker, and the sand wasquantitatively filtered through a numbered and weighed circle of Whatman No. 41 filter paper. The filterpaper was rinsed three times with deionized water, folded, and dried overnight in an oven at 110C.After drying, both the aluminum weighing pans and the filter papers were weighed. The weight of clay inthe weighing pans was corrected for the weight of (NaPO 3) 6in the blank. The clay and sand contents werecalculated for each sample. Silt content was calculated by subtracting the percentages of clay and sandfrom 100%.Organic matter in the sample has been found to distort the determination of clay-size content. Therefore,the samples that contained more than 1% organic carbon were treated with 30% hydrogen peroxide (H 2O 2) .We also found it necessary to treat the upper two samples from each core with H 2O 2. Approximately 12grams of