C. Determination
Place sample, contg ≥45 mg SO2, in distg flask, using H2O for transferring, if necessary. Dil. To ca 400 ml with H2O. Add 90 ml HCL (1+2) to separator and force HCL into flask with gentle pressure. Start N Flow steady stream of bubbles. Heat flask to cause refluxing in 20-25 min (ca 80 volts on 7 amp transformer). When steady refluxing is reached, apply line voltage and reflux 1.75 hr. Turn off H2O in condenser and continue heating until inlet joint of first U-tube shows condensation and slight warning. Remove separator, and turn off heat. When joint at top of condenser cools, remove connecting assembly and rinse into second U-tube. Attach crossover tube to exit joint of frist U-tube, rotate until open ends touch, add drop Me red, and titr. With 0.1 N NaOH just to clear yellow , mixing with gentle rocking. 1 ml 0.1 N NaOH = 3.203 mg SO2. Titr second U-tube similarly. If alternative app. Is used, disconnect, and rinse buld D and tube A with few ml H2O into Kuderna-Danish app. B, C. Add 2 drops Me red and titr. With 0.1 N NaOh.