a. PHYSICAL DESCRIPTION. The heart of the Equiphase Triple Point of Water Cell is
a cylindrical glass container or inner cell having a re-entrant tube which serves as a
thermometer well. The inner glass cell is nearly filled with high-purity, gas-free water,
and is evacuated to the required low pressure and sealed. Insulating material cradles the
glass cell in a stainless steel jacket, providing both thermal insulation and mechanical
protection. A removable cover protects and insulates the top part of the glass cell. The
thermometer well is 10 mm in diameter and 35 cm in length and is designed to receive
platinum resistance standard thermometers commonly in use. Partial freezing of the
sealed-in water, following by partial melting, establishes the triple point temperature
(0.0100C) which is transferred through the well to an inserted thermometer. The
Equiphase Cell is made from the best commercial glass available - if scratch marks
appear on its surface, however, there will be no effect on its operation or reproducibility.
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