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Magical expanding soap – the funny microwave and soap experiment inspired by Jacques Charles.

Ivory Soap circa 1800s

This experiment will make you bend over laughing!

Ivory soap differs from most other brands in that it floats in the water. The reason – there is air whipped into the soap which makes it lighter than water. The small air pockets in the soap make for a very interesting effect when the soap bar is heated up.

  1. Take a bar of ivory soap and place it on a paper towel
  2. Place the bar in the microwave and microwave for 2 minutes
  3. If your microwave has a window, watch the soap bar as it microwaves.
  4. Allow the bar to cool for 1 minute before taking it out of the microwave

Weird huh? The bar of soap will expand into a huge, billowy, puffy mass of white stuff – looks like clouds! The effect you see is similar to the effect popcorn produces when it is cooked. Soap contains water molecules and in the case of Ivory soap, which has air pockets whipped into it, when the water turns to vapor during heating, the vapor is trapped in these little air pockets. This causes the soap, which becomes soft and pliable when heated up, to expand.

About Charles’ Law

French physicist scientist Jacques-Alexandre-César Charles

When heated, the water molecules begin moving very fast and away from each other and hence, the expanding soap effect we see in this experiment. This is a demonstration of Charles’ Law (named after the guy with the glassy looking eyes pictured here) which states that as the temperature of a gas increases, so does its volume. Similarly, if you decrease the temperature of a gas, its volume will decrease proportionally. This law is named after the French physicist Jacques Charles who discovered it in the late 18th century. It is represented mathematically as:

V1/T1 = V2/T2

Where V1 and T1 are the initial volume and temperature of the gas, and V2 and T2 are the final volume and temperature of the gas, respectively.

It is important to note that Charles’ Law only applies to ideal gases, which are gases that follow a set of idealized assumptions. Real gases may deviate from this law at high pressures and low temperatures.

Interesting fact

For more than 75 years, Ivory’s most famous feature – its ability to float – grew to legendary proportions.  But Ivory’s unique characteristic was actually the result of a mistake! The story begins with an employee who forgot to shut off the soap-making machine when he went to lunch. He returned to find the soap mixture puffed-up and frothy. However, because the longer mixing time had not changed the ingredients in any way, the soap was finished and shipped as usual.

About a month later, when P&G started receiving requests for more of the “floating soap,” the accident was discovered. The forgotten lunch-time mistake had produced a unique floating soap!

Experiment Supplies

Supplies: Soap

Image Credits

In-Article Image Credits

French physicist scientist Jacques-Alexandre-César Charles via Britannica Encyclopedia by Library of Congress, Washington, D.C. (Digital File Number: LC-DIG-ppmsca-02185) with usage type - Public Domain
Ivory Soap circa 1800s via Wikimedia Commons by Procter and Gamble Heritage Center with usage type - Creative Commons License. July 22, 2016

Featured Image Credit

Ivory Soap circa 1800s via Wikimedia Commons by Procter and Gamble Heritage Center with usage type - Creative Commons License. July 22, 2016


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