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Science Concepts

Types of Gases for Balloons

Hydrogen balloon-filling apparatus
Courtesy of the Library of Congress

Hot air
Hot air was the first gas used for balloons and is also the gas most people associate with passenger balloons. Brothers Joseph and Etienne Montgolfier built and launched what they called “smoke balloons.”

They believed that a special gas released from burning things made their balloons float, but today we know that the hot air, not the smoke particles, made the balloon float. Particles in the smoke may have helped seal the surface of the balloon, which would have made the balloon more efficient at holding in the hot air.

The buoyancy of modern hot air balloons is controlled with a burner. As the burner heats the air inside the balloon, it expands and becomes less dense, which makes it lighter than the cooler air around the balloon, and it floats.

Hydrogen
Hydrogen is the lightest and most buoyant of all gases: it weighs about seven percent of what air weighs at the same temperature and pressure. It was first used by French physicist Jacques Charles in a passenger balloon in 1783, the same year that the first passenger hot air balloon was launched by the Montgolfier brothers. Charles and other balloonists after him made hydrogen from sulfuric acid and iron filings mixed in a wooden barrel.

Hydrogen also has the distinction of being the simplest and most common element in the universe. If you weighed the universe and divided it into elements, about 75 percent would be hydrogen.

Want to learn more about hydrogen?
Elementary level:
http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html
http://www.chem4kids.com/files/elements/001_speak.html

Middle School level:
http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html
http://www.historyforkids.org/scienceforkids/chemistry/atoms/hydrogen.htm
http://education.jlab.org/itselemental/ele001.html

High School/Adult level:
http://education.jlab.org/itselemental/ele001.html

Helium
Helium is the second-lightest gas in the universe—only hydrogen is lighter—and weighs about 14 percent of what air weighs at the same temperature and pressure.

Many modern gas balloons are filled with helium, including the Conner Prairie balloon, because it won’t burn or explode, unlike hydrogen and coal gas. However, helium is much more difficult to acquire than hydrogen. In 1859, hydrogen was known and could be produced by mixing iron and sulfuric acid. Helium wouldn’t be discovered for another nine years, and then it was only known to exist on the sun! Its name is derived from the Greek word helios, meaning sun. It wouldn’t be found on earth for another 27 years after that.

Today’s helium is tapped from underground wells, where it’s usually mixed with natural gas. Despite its rarity on earth, however, helium is the second most common element in the universe. If you weighed the universe and divided it into elements, about 23 percent would be helium.

Coal Gas
Coal gas was used in 1859 to fill gas balloons because it was lighter than air—it weighs about 33 percent of what air weighs at the same temperature and pressure—though it was made for another purpose. Coal gas burns well and was mass-produced in large factories (gas plants) for light, heat and cooking. It was used in many balloons because it was cheaper than hydrogen, another buoyant gas, and available in many cities.

To make coal gas, gas plants heated coal and caught the gas that came out. Coal gas is actually a complex mixture of many gases, including hydrogen, methane and carbon monoxide. Gas plants also purified the gas by cooling it and bubbling it though containers of water. Coal tar and ammonia were “impurities” in the coal gas, but were useful for other things and were sold by the gas plants.

Both hydrogen and coal gas were used in balloons in 1859, but were both dangerous because they can burn or explode. Modern gas balloons, including Conner Prairie’s balloon, use helium, which does not burn or explode.

Middle School level:
http://fossil.energy.gov/education/energylessons/coal/index.html

High School/Adult:
http://www.fossil.energy.gov/programs/powersystems/gasification/howgasificationworks.html

Coal Tar
Purifying coal gas leads to several by-products, including coal tar. Coal tar was used until recently in road paving products and wood preservatives. Later (1850s and beyond) scientists discovered that the many complex chemicals in coal tar were useful in making medicines, perfumes, artificial flavorings and the first chemical dyes. These dyes were used to make bright colors for clothing and paints, but also affected medical science. Stains derived from coal tar were used by microbiologists to color germs, which led to a better understanding of the types of germs, how they worked and how some caused diseases.

Middle School level:
http://www.atsdr.cdc.gov/tfacts85.html#bookmark02
http://www.eia.doe.gov/kids/energyfacts/sources/non-renewable/coal.html http://www.sciencenewsforkids.org/articles/20031126/Note3.asp

High School/Adult level:
http://www.atsdr.cdc.gov/tfacts85.html#bookmark02

What makes a balloon float?
It’s pushed up by the air around it. Air pressure is higher closer to the earth, because of all the weight of the atmosphere pressing down. We don’t feel it because we’re used to it, but you may have felt the same effect when swimming underwater. As you swim deeper you can feel the water pressing harder on you. It’s the same with air.

Pressure from the air presses on the balloon from all around it, but the pressure is higher at the bottom of the balloon than at the top.

A balloon is pressed upward by the pressure underneath it. If that difference in pressure is enough to overcome the weight of the balloon, it goes up.

The point at which a balloon floats is when it weighs less than a balloon-sized volume of air.

Want to learn more about how buoyancy works?

High school/adult level:
http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy.html#buoy

Controlling Gas Balloons in 1859 Most balloons in 1859 weren’t hot air balloons—they were gas balloons. That means they were filled with a gas that was lighter than air, even at the same temperature. Balloonists like John Wise used gases like hydrogen or coal gas to fill their balloons, as helium hadn’t been discovered yet.

• Filling the Balloon In a typical 1859 gas balloon flight, a balloonist filled up the balloon with gas and sealed it. It was tied down until the launch to keep it from floating away. At that moment, the balloon had as much lift as it was going to have for the whole flight. Gas would slowly leak out bit by bit, and the balloon would gradually sink.
• Going Up Balloonists compensated for the balloon’s tendency to sink over time by initially adding a lot of extra weight, or ballast, to the balloon. Ballast—often sand kept in sacks—could be dumped overboard to keep the balloon from sinking as the gas leaked out, or to make the balloon go higher.
• Going Down Letting gas out of the balloon made it go lower. There was a valve in the top of the balloon that the balloonist could pull open with an attached rope. Balloonists would most often do this if they wanted to land, but also if they were going too high to be safe or if the balloon expanded and was in danger of popping.
• Going Sideways Balloonists could make a balloon go up or down, but they had to ride the winds to go sideways. There were many experiments that tried to control a balloon’s direction, but none were very successful in 1859. Instead, balloonists tried to get into a wind going in the direction they wanted to go. They discovered that winds move in different directions at different altitudes.
• Rivers of Wind John Wise discovered that there was a wind at a certain height that was always blowing from west to east. He called this the “River of Wind” and thought it could be used to make balloon travel predictable and practical. We call this the Jet Stream today.

Want to learn more about the science of ballooning?

High School/Adult level: A free online version of John Wise’s book describing ballooning methods he used and his adventures. http://books.google.com/books?id=udwpAAAAYAAJ&pg=PA23&dq=%22john+wise%22+through+the+air&as_brr=1&ei=HuGeSYWRKI6yMISnzMEL&client=firefox-a#PPP6,M1