A reusable hot pack made of a supersaturated sodium acetate solution that crystallizes spontaneously once triggered by a metal piece releases heat. A balloon filled with hydrogen gas also releases ...

In 1783, hot air balloons became the ... Beginning in the early 1930s the United States Air Force began making forays into the atmosphere using balloons, and what followed laid the foundation ...

Annual hot air balloon ... was the first to use a parachute in 1793. (That was an unplanned success — his balloon ruptured and he had to bail out.) Early on he switched to hydrogen to fill ...