Note 2 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE
George Kamensky translation
To obtain so high a temperature (at which the best kinds of porcelain soften) Langer and Meyer employed the dense graphitoidal carbon from gas retorts, and a powerful blast. They determined the temperature by the alteration of the volume of nitrogen in the platinum vessel, for this gas does not permeate through platinum, and is unaltered by heat.