Lifting gas

It can be easily produced in large quantities, for example with the water-gas shift reaction or electrolysis, but hydrogen has several disadvantages: Helium is the second lightest gas (0.1786 g/L at STP).

But the use of helium has some disadvantages, too: In the past, coal gas, a mixture of hydrogen, carbon monoxide, and other gases, was also used in balloons.

Disadvantages include a higher density (reducing lift), its flammability[6] and the high toxicity[7] of the carbon monoxide content.

Ammonia has been used as a lifting gas in balloons,[8] but while inexpensive, it is relatively heavy (density 0.769 g/L at STP, average molecular mass 17.03 g/mol), poisonous, an irritant, and can damage some metals and plastics.

[citation needed] It has the advantage of not leaking through balloon walls as rapidly as the smaller molecules of hydrogen and helium.

A well-known example is the Rozière balloon which combines a core of helium with an outer shell of hot air.

The gaseous state of water is lighter than air (density 0.804 g/L at STP, average molecular mass 18.015 g/mol) due to water's low molar mass when compared with typical atmospheric gases such as nitrogen gas (N2).

In 2003, a university team in Berlin, Germany, has successfully made a 150 °C steam lifted balloon.

However, it is extremely corrosive, highly toxic, expensive, is heavier than other lifting gases, and has a low boiling point of 19.5 °C.

Its extreme flammability and low lifting power make it an unattractive choice.

Hydrogen cyanide, which is 7% lighter than air, is technically capable of being used as a lifting gas at temperatures above its boiling point of 25.6 °C.

Neon is lighter than air (density 0.900 g/L at STP, average atomic mass 20.17 g/mol) and could slowly lift a balloon.

As early as 1670, over a century before the first manned hot-air balloon flight,[11] the Italian monk Francesco Lana de Terzi envisioned a ship with four vacuum spheres.

A balloon that is designed to lift to extreme heights (stratosphere), must be able to expand enormously in order to displace the required amount of air.

The air is either supplied from diving cylinders or pumped through a hose from the diver's ship on the surface.

The lightness and low density is due primarily to the large proportion of air within the solid and not the silicon construction materials.