摘要：Nitrogen trichloride (NCl3) is considered as a material with unpleasant odor and causing eye irritation in swimming pool. The formation of NCl3 depends on pH and molecular ratio of chlorine to ammonia. When NCl3 was measured by Palin's neutral ortho-tolidine method with oxalic acid, false NCl3 not extracted with CCl4 was observed in the determination of chlorine solution containing a certain organic nitrogen compound such as isocyanuric acid (ICA), hypoxanthine, and dimethyl urea. The false NCl3 disappeared by lengthening the contact time with oxalic acid. In order to measure NCl3 without influence of coexistence of these compounds, NCl3 was extracted with CCl4, and the chlorine of NCl3 in CCl4 layer was mesured by iodometric method. By use of this CCl4-extraction method, the effect of ICA on the formation of NCl3 from ammonia and chlorine was studied. The quantity of NCl3 formed decreased by the addition of ICA. Isocyanuric acid had the same effect even when ammonia in solution was in the chemical form of monochloramine (NH2Cl), and dichloramine (NHCl2). When the dose of chlorine was less than that of breakpoint, ammonia in solution was decomposed without producing NCl3. Thus the separate addition of chlorine gave a practical effect on the decrease of NCl3 in the procedure of breakpoint chlorination.
