EXPERIMENTAL PROCEDURES 65 end of the operation, a small amount of trichlorofluoromethane can be distilled from the excess carbon tetrachloride. The utilization of the antimony fluoride is complete. l,2-Dichloro-l,l,2,2-tetrafruoroethane (CC1F 2 CC1F 2 ). 6° A known quantity of SbF 3 Cl 2 is prepared as described on p. 61. When this iscomplete the reaction vessel is evacuated, and an equimolecular quan- tity of CC1F 2 CC1 2 F is drawn in. The needle valve is closed, and the mixture is heated gradually to 140°, then to 1^0°. The pressure rises. The temperature and pressure readings at the top of the equipment are referred to the vapor-tension diagram, Fig. 1. The needle valve is opened in such way as to permit the passage of CC1F 2 CC1F 2 vapors. These vapors (b.p. 3.6°) are condensed in Dry Ice. When the tetra r fluoride vapors are withdrawn, the trifluoride (b.p. 47°) starts to distil, the temperature rises, and the pressure falls. The valve is closed until
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