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• <br />Determination of Total Sulfur - Continued <br />4. Turn on oxygen; set pressure at 15 psi, flow rate <br />to 0.5 liter/min. <br />5. Fill iodate buret. <br />6. Fill titrating chamber to just above oxygen inlet <br />port on side of chamber and add one measure of starch <br />solution. <br />7. Adjust to proper endpoint with endpoint controls <br />(refill iodate buret after endpoint adjustment). <br />8. Place sample crucible on pedestal, making sure it is <br />centered; carefully raise sample into uppermost <br />position and close switching lever. Make certain <br />sample platform seals when closed. <br />9. Push red button on timer to start analysis. <br />• <br />10. Plate current must reach 350-400 ma for at least 15 <br />seconds during the analysis; if not, rerun sample. <br />11. If buret is still changing when timer approaches zero <br />position or combustion has not taken place, set timer <br />switch to off position, which keeps furnace operating, <br />and maintain in this position until buret reading <br />is stable for 2 minutes. <br />12. Lower sample platform and remove crucible with tongs. <br />13. Refill iodate buret. <br />14. Return to step 6 and proceed. (Drain titration vessel <br />after every third sample, refill and adjust endpoint). <br />15. After shutdown, drain titration vessel, rinse with <br />water, refill with weak ammonium hydroxide solution, and <br />let air flow bubble through for several minutes (removes <br />precipatate buildup from titration vessel). Drain and <br />flush with water several times. Refill with water <br />until next group of samples are analyzed. <br />• <br />Refer to Leco instruction manual for any deviation to the above <br />instructions and any maintenance of the furnance or titration <br />apparatus. <br />6-58 <br />