Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

34 EXPERIMENTAL METHODS FOR SLOW REACTIONSFig. 25. LeRoy still. From ref. 113.The different fractions obtained in this way may be analysed later by variousmethods. Liquids, sealed in sample tubes, and gases may be analysed by GLC orGSC; gases such as halogens, hydrogen halides or CO, may be absorbed on varioussolids and subsequently analysed quantitatively by potentiometric titration techniques.Alternatively, analysis may be carried out in situ or small samples withdrawnfor direct GLC or GSC analysis. These techniques will be discussed in detaillater.3.3 PHOTOCHEMICAL SYSTEMS (see also Volume 3, Chapter I)3.3.1 IntroductionMost of the experimental techniques for thermal systems apply here. One importantexception is that for experiments using Hg 2537A radiation, the vacuumsystem must be completely free from mercury, i.e. no mercury diffusion pumps orMcLeod gauges should be used, unless mercury-sensitised reactions are being studied.Even the use of iodine, gold or similar amalgamating metals does not completelyfree a particular section of the vacuum system from mercury. There is anexcellent treatise on photochemical reactions by Calvert and Pitts’.