“…We tried sulfur hexafluoride, used to prevent dielectric breakdown in high-voltage equipment, but the pump cycle took too long. Thus, we continued with the gases that others had used, including carbon dioxide, ,, helium, ,, and argon. ,− We did not use neon because of its high cost. Unfortunately, we were unable to examine 1 because we could not accomplish the crystallization step, but previous workers have done so…”