FTP, name this pressure and temperature at which one may isolate all of a substance's three phases.
Many of these exist for substances with multiple polymorphs, such as silver iodide and aluminum silicate, and helium-4 has two of them, called "lambda" ones, because of superfluidity. If a substance has n solid phases, it will have n choose three of these. Gibbs's phase rule states that there exist one fewer degrees of freedom under this condition than the number of components in the mixture. One aspect of it for water is the second reference point of the Kelvin scale. FTP, name this pressure and temperature at which one may isolate all of a substance's three phases.
Many of these exist for substances with multiple polymorphs, such as silver iodide and aluminum silicate, and helium-4 has two of them, called "lambda" ones, because of superfluidity.
{triple} point