How Can You Make Water Invisible?

posted: 04/11/12
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Is invisible water for real? Well, yes and no.
Charles C. Place/Photographer's Choice/Getty Images

The myth concerning invisible water might be proven true if you took it at face value but changed it to: "Can you make a boat look like it's floating on invisible water?" The answer to that question would be a resounding yes.

The Tide Is High

The trick is that instead of water -- invisible or otherwise -- the myth capitalizes on the properties of sulfur hexafluoride. The molecules of that particular gas are comprised of one sulfur atom surrounded by six fluorine atoms. Much denser and heavier than other molecules in the air, sulfur hexafluoride will not only rest easy in an open-topped container like an aquarium, it can also support the weight of very light solid items like tinfoil boats.

But I'm Holding On

Now, invisible water is cool and all, but how about upside down water? HowStuffWorks staff writers took care of confirming this myth, but feel free to test it out on your own -- preferably over a sink until you get the hang of it. Take a cup and fill it to the brim with water, then place an index card over the top. Slowly tilt the cup until it's upside down (don't worry if a little water falls out while you're turning it) and then very gently take your hand away from the piece of paper. If everything went as planned, the piece of paper should remain in place -- along with all the water.

Sound strange? The reason this experiment works is because of air pressure. At sea level, the air in the atmosphere exerts roughly 14.7 pounds per square inch of pressure; the number gradually decreasing towards higher altitudes. People don't normally take much notice of that force because the air in our bodies is naturally pressurized to the same level -- but the phenomenon can become more noticeable when you're riding in an elevator or flying in an airplane. Getting back to the experiment, however, the water in the cup exerted only a small amount of pressure on the index card, especially in comparison to the atmosphere of the room. With its nearly 15 psi, air pressure was easily sufficient to keep the setup intact.

If you're still a little confused, picture the Earth's atmosphere (the gases, water vapor and such that surround us) as an ocean of little molecules. We're way down on the ocean floor, so if we weren't acclimatized to the pressure, we wouldn't be able to survive. And similar to how oceanic life is shaped by marine elements like waves and currents, depth, and temperature, so, too, are our lives affected by changes in the atmosphere -- only we tend to call this weather. Many analogous factors come into play; high and low pressure fronts sweep across continents and temperature changes stir the air. Our atmosphere is an intricate, and weighty, collection of gases, vapors and particles which are constantly shifting every day.

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