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14. Fill "Titration Vessel" approximately one-third full with the HCl <br /> solution. <br /> 15. Turn on oxygen. Set the pressure to 15 psi, and the flow rate to 1.0 <br /> liter per minute. NOTE: 0:)Wgen flow must be started before starch is added. <br /> 16. Raise the "Locking Mechanism Handle" WITHOUT a sample crucible on the <br /> pedestal, and lock in place. NOTE: Make sure there is an airtight contact <br /> between sample platform and combustion chamber by observing a vigorous <br /> bubbling in the "Titration Vessel" chamber. <br /> 17. Add one measure (5 ml) of starch solution. NOTE: If solution in <br /> "Titration Vessel" chamber turns turbid or yellow after starch solution is <br /> added, turn off the instrument following steps 33 through 39 and make NEW <br /> starch solution. <br /> 18. Set "Titrate-Endpoint" switch to "Endpoint. " <br /> 19. After a feu seconds when titrant level in "Iodate Buret" has stopped <br /> falling (Buret reading should be no more than 0.004) the solution in the <br /> "Titration Vessel" chamber should be a deep blue. NOTE: If the solution <br /> is a pale blue or almost black, turn off the instrument following steps 33 <br /> through 39 and make NEW starch solution. <br /> 20. Set "Titrate-Endpoint" switch to middle position and lower "Locking <br /> Mechanism Handle." <br /> 21. Refill "Iodate Buret." <br /> 22. Place sample crucible on pedestal, making sure it is centered, and <br /> carefully raise "Locking Mechanism Handle" and lock in place. <br /> NOTE: Make sure there is an airtight contact between sample platform and <br /> combustion chamber by observing a vigorous bubbling in the "Titration <br /> Vessel" chamber. <br /> 23. Set "Titrate-Endpoint" switch to Titrate, or if it is known that sample <br /> will evolve S02 slowly, set switch at Endpoint. The Endpoint setting acts <br /> as a "Fine Control" allowing buret valve to discriminate smaller increments. <br /> 24. Push RED button on timer to start analysis. <br /> 25. Plate current must go to 400-450 ma for at least 2 minutes during the <br /> analysis; if not, reweigh and rerun sample. <br />} 25. Adjust rheostat to prevent plate current from exceeding 450 ma. <br /> 3 <br /> 27. When buret reading does not change for 2 minutes, and Plate Current <br /> has achieved 400 to 450 ma, it can be assumed that all of the sulfur has <br /> been removed from the sample. If buret reading is still changing when timer <br /> shuts off instrument, set Timer Switch to OFF, which restarts furnace, leave <br /> furnace on until buret is stable for 2 minutes, then turn Timer Switch to ON. <br /> 54 <br /> A <br />