A technique for in situ measurement of the conductivity of water in 'triple point of water' cells

Sealed glass ampoules made for the realization of the triple point of water as a thermometric reference point, 0.01 degrees C, must be filled with wat er of the highest possible purity. This paper discusses a simple electrical technique for measurement of the conductivity of high-purity water within such cells, and presents calculations of the calibration factor in this geo metry. The technique is then applied to a large set of cells, some dating b ack up to 40 years, and the results are compared with measurements of the c ells' triple point temperature. The measurements indicate that the effectiv e ionic conductivity of the impurities in the cells is as low as 2 mS m(2) mol(-1).