H. Allen Smith, "The Achievement of H.T. Wensel," in Clifton Fadiman, ed., The Mathematical Magpie
(New York: Simon and Schuster, 1962), pp. 141-142 (at 142):
The exact temperature of hell cannot be computed, but it must be less than 444.6° C., the temperature at which brimstone or sulphur changes from a liquid to a gas. Revelations [sic] 21:8: "But the fearful, and unbelieving ... shall have their part in the lake which burneth with fire and brimstone." A lake of molten brimstone means that its temperature must be below the boiling point, which is 444.6° C. If it were above this point it would be a vapor and not a lake.
As the article points out, hell (below 445° C. = 833° F.) is actually cooler than heaven (525° C. = 977° F., computed from Isaiah 30:26).