What is claimed is:
1. Device for measuring temperature and fugacity of a material, said device comprising a solid electrolyte sensor, which electrolyte is conductive to ions of said material, thermally stable and chemically inert to said material, and has low permeability to neutral materials and other ions, a passageway for a reference fluid in said sensor, said passageway including a capillary restriction which is of a cross-sectional area no greater than one-tenth the area of the remainder of said passageway so as to produce non-turbulent flow therein, a first metallic conductor lead on the outside of the sensor and exposed to said material, a second metallic conductor lead on the inside of the sensor in said passageway generally proximate said capillary restriction and generally opposite said first lead, said leads in contact with said solid electrolyte thereinbetween, chemically inert to, non-contaminating to and not appreciably miscible with said material and said electrolyte and having a high melting point and low vapor pressure,
electromotive force measuring means electrically connected to said leads to measure the E.M.F. therebetween, and pressure drop means to measure the pressure drop of the reference fluid when flowing through said capillary, whereby the pressure drop measurement permits determination of temperature of said material, and said E.M.F. measurement together with said determined temperature permits determination of the fugacity of said material.
2. Device of claim 1, wherein said sensor is elongated, and said passageway extends along the length thereof.
3. Device of claim 1, wherein the fluid resistance of the capillary is at least 100 times greater than the fluid resistance of the passageway upstream of the capillary.
4. Device of claim 1, wherein the passageway upstream of said capillary is at least 10 times as long as the length of said capillary.
5. Device of claim 1, wherein each of the metallic conductor leads, or fugacity sensor electrodes, are of the same metal.