Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

4 ANALYSIS 103IFig. 72. Quartz fibre manometer. From ref. 22c.fringes. For gases of different refractive index the band system is displaced sideways.The displacement can be compensated for by changing the inclination ofone of the glass plates, which is attached to a micrometer screw with a measuringdrum. The principles of operation of the interferometer have been described inrefs. 22c and 335. A calibration curve has to be constructed. In the range of0-15 % germane, the precision is 0.059 mole %. The method has also been usedto analyse mixtures of acetylene and dimethyl ether in a flow system336.A photoelectric recording interferometer has been designed by Burnett et al. 337.In this particular case, the temperature rise during a liquid-phase polymerisationcaused a change in refractive index which could be related to the rate of the reaction.It was possible to measure a temperature change of degrees at roomtemperature. This technique might well be adapted to study adiabatic reactionsin the gas phase. Both refractive index measurement and interferometry are usedextensively in combustion studies to determine temperature gradients and finaltemperatures3 38.4.5.10 Dielectric constantDielectric constants of substances vary widely and can be measured with considerableaccuracy. Despite the potentialities of this technique for kinetic studies,it has been little used. (As an example, see Melville et a1.339, who followed vinylpolymerisation in the initial stages in this way.)References pp. 104-1 11