Chlorinated hydrocarbons are widely used as industrial solvents. Their concentrations in air, therefore, should be often checked for health supervision in the factories where those solvents are used. So-called detector tubes may be used, but these are not applicable for every chlorinated hydrocarbons. In this study, the determination method of chlorinated hydrocarbons in air, particularly that of 1, 1, 1-trichloroethane in air was examined in some points. 1) Principle of the determination. Vapor of 1, 1, 1-trichloroethane is collected by adsorption on silica gel in U-tube. Then, extraction of the vapor from silica gel is made by isopropyl alcohol at 52°C, followed by filtration. Afterwards, hydrolysis of the above filtrate is made at 52°C by dissolving some pellets of potassium hydroxide. Then, neutralizing with 5% acetic acid and adding 1 ml of 5% potassium chromate as an indicator, determination is made for hydrolyzed chlorine ion by titration with 0.1N silver nitrate. 2) Rate of hydrolysis for various periods. Four or ten pellets of potassium hydroxide were dissolved in 20 ml of test solution of 1, 1, 1-trichloroethane (3.360 grams per liter of isopropyl alcohol) to observe the rate of hydrolysis for various lengths of time at 52°C. It was found that 10 pellets of potassium hydroxide were more effective to hydrolysis than 4 pellets. The hydrolysis with 10 pellets of potassium hydroxide reached an equilibrium by 72 hours, and the rate of hydrolysis was 75%. The rate of hydrolysis of carbon tetrachloride and 1, 1, 2, 2-tetrachloroethane was also examined. Their rates of hydrolysis reached an equilibrium by 24 hours at 52°C, with the rates 96% and 66% respectively. 3) Rate of extraction for various periods. The apparatus for vaporizing 1, 1, 1-trichloroethane was designed as shown in Figure 2. Two U-tubes containing silica gel were connected with the above apparatus in series. Silica gel adsorbing 1, 1, 1-trichloroethane vapor was extracted by 50 ml of isopropyl alcohol to examine the rate of extraction for various periods at 52°C. It was found that 2 hours were sufficient to extract 1, 1, 1-trichloroethane and the rate of extraction was 96%. In any extraction periods, 1, 1, 1-trichloroethane was not detectable in the second U-tube revealing that one U-tube is enough to sample. 4) A formula for calculation of 1, 1, 1-trichloroethane concentration in air is given in Table 6. 5) The determination methods of the other chlorinated hydrocarbons in air may be established in the similar procedures as examined in 1, 1, 1-trichloroethane of this study.
