Sulfur dioxide in sulfite cooking liquor - T 604 cm-22

This method is for the volumetric analysis of sulfite liquors used in the manufacture of sulfite pulp.  The method is basically that developed by G. V. Palmrose (1) and is based on titration with potassium iodate for the total SO2 and titration with sodium hydroxide for the free SO2.  Liquor containing lignin derivatives requires corrective procedures which are given. 

Sulfur dioxide in cooking liquor can be present as one or two of the following three forms:  (1) dissolved sulfur dioxide and sulfurous acid; (2) ammonium, calcium, magnesium, or sodium bisulfite; or (3) ammonium or sodium sulfite (monosulfite).  Four bases, ammonium, calcium, magnesium, and sodium have been commercially utilized; limited solubility problems with calcium and magnesium monosulfites restrict these liquors to combinations of (1) and (2), whereas sodium and ammonium monosulfites are soluble in the upper ranges of pH and allow combinations of (2) and (3) to be utilized.