Observations of Hydrogen at Room Temperature (25{degrees}C) and High Pressure (to 500 Kilobars).

Hydrogen becomes a solid at 25 degrees C when subjected to a pressure of 57 kilobars. The high-pressure phase appears as a transparent crystalline mass. The refractive index of the high-pressure phase increases sharply with pressure, indicating a density increase of similar magnitude. At 360 kilobars the calculated density of the high-pressure phase is 0.6 to 0.7 grams per cubic centimeter.