for paper coating clays. In addition, a finer particle-size distribu- 

 tion of Si02 was generated from the commercially available Fisher No. 

 S-135 by allowing these solids to settle for 25 minutes through a 

 specified distance in a column of distilled water at 20° Celsius. The 

 solids finer by weight than 15 micrometers were calculated to be 

 remaining in suspension in this column of water from tables presented 

 by Trask (1968) and from Casagrande's nomographic solution of Stokes' 

 Law given in American Society for Testing Materials (1968). The sus- 

 pended particles were decanted, oven-dried for 24 hours at 100° 

 Celsius, ground fine with a porcelain mortar and pestle, and analyzed 

 for size distribution by the American Society for Testing Materials 

 (1968) method performed for the other mineral solids. This particular 

 size distribution of Si02 particles (median size 6.2 micrometers) is 

 referred to in this report as <15 micrometers Si02 (actual analysis 

 shows about 5 percent of the particles are >15 micrometers) (Fig. A-1, 

 Table A-1). 



The natural sediments collected from the Patuxent River were 

 analyzed by a procedure slightly modified from the above method. Pre- 

 liminary work showed that this material was approximately 75- to 80- 

 percent salt and water by weight. Appropriate triplicate) volumes of 

 this natural material were removed from the holding tanks. These 

 volumes were calculated to contain between 5- and 10-gram dry solids 

 (inorganic). Also, these volumes were corrected upward for the amount 

 (weight) of organic matter present (see method of analysis below). 

 These quantities of solids were placed into large Pyrex beakers (1-liter 

 capacity) and an appropriate amount of 30 percent hydrogen peroxide 

 (H2O2) was added to each beaker. The amount (volume) of H2O2 (30 per- 

 cent) needed to oxidize the organic matter present in the sediment was 

 found to be a volume which would produce a final concentration of H2O2 

 in the sediment volume of approximately 5 percent. The oxidation 

 reaction was quite violent initially. The reaction was allowed to pro- 

 ceed overnight in a hood with air bubbling slowly through the sediment- 

 H2O2 mixture to remove the excess H2O2. 



The next day, when gas evolution had ceased, 750 milliliters of 

 deionized glass-distilled water were added to each beaker. The sedi- 

 ment was resuspended by stirring with a glass rod, and allowed to 

 settle. The supernatant was decanted very carefully, and another 750 

 milliliters of deionized glass-distilled water rinse were added to 

 each beaker. 



A 0.2-milliliter sample of supernatant water was then taken from 

 each beaker and the dissolved ion concentration of each solution was 

 determined with the freezing point depression osmometer normally used 

 in our hematological analyses. Salt concentration was read from a 

 standard curve relating freezing point depression and osmolal concen- 

 tration to sodium chloride (NaCl) concentration in mg kg"-^ water. 

 If the salt concentration was greater than 300 milligrams NaCl kg"-^ 

 water, the suspension was allowed to settle, the clear supernatant 

 was decanted, and an additional rinse of 750-milliliter deionized 



42 



