Sulphur hexafluoride as a gas-air tracer.

Give method for collecting and analysing sulphur hexafluoride used as a tracer gas. The gas is separated by gas chromatography from other components of moist air on columns of silica gel and activated carbon in series and is detected by electron-capture analysis in concentrations near 1 p.p.b. states that sensitivity can be enhanced at least 2000-fold by freeze-out concentration. States that SF6 backgrounds in air are undetectable except near leakage sources such as transformers. Describes test using SF6 to measure chimney effluent dilution and shows that results were close to calculated values.