The Winkler method for dissolved oxygen in water is based on the rapid oxidation of solid Mn(OH)2 to Mn(OH)3 in alkaline medium. When acidified, the Mn(III) readily releases iodine from iodide. A 250-mL water sample, in a stoppered vessel, was treated with 1.00 mL of a concentrated solution of NaI and NaOH and 1.00 mL of a manganese(II) solution. Oxidation of the Mn(OH)2 was complete in about 1 min. The precipitates were then dissolved by addition of 2.00 mL of concentrated H2SO4, whereupon an amount of iodine equivalent to the Mn(OH)3 (and hence to the dissolved O2) was liberated. A 25.0-mL aliquot (of the 254 mL) was titrated with 14.6 mL of 0.00897 M thiosulfate. Calculate the mass in milligrams of O2 per milliliter sample. Assume that the concentrated reagents are O2 free and take their dilutions of the sample into account.