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r s APPENDIX Le 2X,,GEN D,ss (cont'd) Pag_-e� 22 o 6. Measure 200 mL of the prepared solution by filling a clean 2550-mL graduated cylinder to the 200 mL mark.Pour the solution into a clean 250-ML erlenmeyer flaskAS . T. if performing a hand-held titration,* itration,attach a clean,straight-stem delivery tube to a 0.2000N Sodium Thiosulfate Titration CaMdge.Twist the cartridge onto the titrator body.If the Digital Titrator!s to be attached to a laboratory stand,use a:Jean 40°delivery tube. $. Plush the delivery tube by turning the delivery knob to eject a few drops of titrant.Reset the counter to zero and wipe the tip. g. Titrate the prepared solution Sodium Thiosulfate,0.2000N, to a pale yellow color. on and swirl to mix.A dark blue color will develop. 10. Add two droppersful of Starch Indicator Soluti 11, Continue the titration until Che solution changes from dark b',ue to colorless. 12. head the number of digits from the digital counter window.Divide the reading by 100 to determine the coneenuation of dissolved oxygen(in mg/L). Procedure for Digits!Titrator Method(DRBLIS) 1. Collect a water sample in a clean 60-mL glass-stoppered BOD bottle by allowing the sample to overflow the bottle for two ar three minutes.This ensures there are no air bubbles.trapped in the bottle 2. Add the contents of one Dissolved O 2 Res- xygen 1 Reagent Powder Pillow and one Dissolved oxygen gent PowderPillow. to the bottle and invert several times to rnix.A 3, Immediately insert the(topper so that no air is trapped a if dissolved ox en is resent or white if flocculent precipitate will form.It will be brownish-prang oxygen 1? oxygen is absent. i 4. Allow the sample to stand u;-,tilr.See Note C. the floc has settled and leaves the top half of the solution clear.Again C. vert the bottle several times to mix and let stand until the upper half of the solution is clea nt 5, Remove the stopper and add the contents ra teanpe nts$r bu bubbles ne Dissolved n the bottle,and in 3 nvert se eralei Pillow. to mix.The the stopper,being careful not to p y flat will dissolve and leave a yellow color if dissolved oxygen is present. 6. Accurately measure 20 mL of the prepared solution and transfer it 10 a titration flask, ery tube to a 7. if performing a hdium 0 and-held �ti'i wise the cartridge a on,attach a clean, tthe titter deli, y.If the Digiti T�or its to be Thiosulfate Titration Cartridge. attached to a laboratory stand,use a clean 90'delivery tube. $, Flush the delivery tube by turning the delivery knob to eject a few drops of titrant.Reset the counter to zero and wipc the tip: 4. Titrate the prepared solution with Sodium Thiosulfate,0.2000N. until the sample changes from yellow 4 to colorless. 10. digital counter window.Fdultiply the reading by 0.1 to determi Read the number of digit-from thene the re ,h k concentration of dissolved oxygen(in mg1L). Notes sresults ce, A. Sampling and sample handling we important considerations it_obtaining meaningful tarbuientem- e t solved oxygen content of the water being tested can be expected to change with depth, pemture,sludgf deposits,light,microbial the curatrs.A single dis- ¢over-all condition condition oixing,travel rt a body or wame and other teraSe eml samples solved oxygen test rarely reflects taken at different times,locations and depths are recommended for most reliable results.Samples must be immediately on collection..--------------------- -------- ------ --- ------- --— - 1 given in Pan 1. ( ter The solubility of oxygen in pure water at various temperatures and pressures is g E = Conversions. F _ c � 1