The Isotech Mercury Cell Model is constructed in a rugged, sealed stainless steel enclosure allowing the triple point of -38.8344°C to be realized both easily and safely. Total Confidence The embodiment of the Mercury Triple Point Cell was originally developed in the US with a very close cooperation between Henry Sostmann and Dr. Furukawa of N. B. S. (now NIST) over twenty years ago. The physical size, materials and metal purity are identical to this original design. The Mercury is distilled four times leaving impurities of 10 to 15 parts per billion. The cells made by Isotech still use the original design, purity and supplier of Mercury. In international intercomparisons the cells made by Isotech have always been within the National Laboratories uncertainty of calibration and with over 20 years of successful use throughout the world the cell embodies the finest traditions of production and use. After more than 20 years Dr. Furukawa opened some of the original cells and the Mercury was still above 99.99995% pure. A reflection of the long term performance of the design.