Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

8EXPERIMENTAL METHODS FOR SLOW REACTIONSiTo H.V.To$asstorage manifold (GSM.)1-Gas inletL.V. = Low VacuumH.V. =High VacuumTo LYTo MC Leodgauge etc.H.V. 4To GSM.I?ig. 4. High-vacuum system for kinetic studies.been constructed by Judge and Luckey2*. All-metal taps are available commerciallywhich are bakeable, have rapid operation and provide good sealing; onedraw-back is their price, and once again chemical reaction may occur.Details of a typical vacuum line for a gas phase kinetic study are given by MaccollZ3.A useful set-up is to have a manifold of large-diameter glass tubing leadingfrom the pumping system, to which the different sections, storage and introduction,mixing and reaction vessels and analytical section, are connected (Fig. 4).This manifold system has the advantage that each section may be evacuated independentlyof the others.3.1.2 Temperature controlThere are three general methods for maintaining a RV at a particular temperature:thermostats, furnaces and vapour baths29.At temperatures close to 20+20", water is a suitable liquid for a thermostat.At higher temperatures it is more convenient to use a fluid such as silicone oil,or above 2W, molten metals. A typical furnace is shown in Fig. 5. A silica formeris wound with nichrome wire such that the pitch decreases from one end to the centreand then increases again to the other end. Since heat losses are greatest at theends this provides a rough correction. An inconel tube also evens out the tempera-