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| | Helium (Site not responding. Last check: 2007-09-21) |
 | | The goal was to supply barrage balloons with the non-flammable lifting gas. |
 | | Some of this gas was used in the world's first helium-filled airship, the U.S. Navy's C-7, which flew its maiden voyage from Hampton Roads, Virginia to Boiling Field in Washington, D.C. on December 7, 1921. |
 | | However, in the Earth's atmosphere, the concentration of Helium by volume is only 5.2 parts per million at sea level and up to 15 miles (24 km), largely because most Helium in the Earth's atmosphere escapes into space due to its inertness and low mass. |
| helium.iqnaut.net (4744 words) |
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