The object of this investigation was to determine the magnitude of the catalytic effects of all the commonly used thermocouple materials in lean mixtures of hydrogen, carbon monoxide, propane, and methane in air.
Up to 1800 F, wires of platinum, palladium, iridium, platinum plus 15% iridium, and the two elements of the Platinel thermocouple were found to catalyze the combustion of mixtures of hydrogen, carbon monoxide, and propane in air. Gold, silver, Chromel, Alumel, and constantan wires showed no catalysis of any mixture. Base-metal thermocouples are therefore recommended for accurate determinations of temperatures of gaseous mixtures containing combustible materials.