In the manufacture of glass bottles accurate control of temperature is necessary, and it is usual to check the temperature of the flowing glass in the channel and again in the feeder and to apply automatic corrections to the fuel supply. Continuous measurement with platinum: rhodium-platinum thermocouples is generally employed.

The thermocouple assemblies installed for this purpose by Honeywell Controls Ltd. at the works of Rockware Glass Ltd. are specially designed for instantaneous temperature measurement under severe conditions. They are fitted with platinum: 13 per cent rhodium-platinum couples in twin-bore refractory insulators and are housed in composite all-metal sheaths. These have a nickel stem passing through the tank wall, welded to a platinum or rhodium-platinum tip 0.2 inch thick, the tip projecting into the flowing glass.

A secondary sheath of impervious mullite protects the assembly for most of its length, but leaves the platinum tip uncovered. To provide the necessary sensitivity for rapid temperature control, the hot junction of the couple is held in contact with the inside of the sheath.