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Have you ever played the fountain game of Coke + Mentos? When you put a mint like Mentos into a bottle of Coke, a lot of bubbles will be emitted instantly, creating a scene like a fountain.

In the 1910's, the game was already a performance project. After a hundred years, people still enjoy it, and some senior players have even done a lot of experiments to find the secret that this bubble fountain can spray higher.

How can you spray so high? | | piyochan2001 / youtube |

The reason why Coke forms a fountain is actually very simple. For Coke soda to have enough gas, you need to dissolve as much carbon dioxide as possible into the water, which requires cooling or pressurization. In bottling plants, soda is usually carbonated under four times the pressure.

When a bottle of Coke is not opened, the pressure in the bottle is higher and there is more gas dissolved in the water. So when you open the bottle, the internal air pressure suddenly drops, and you will hear a "whoosh" sound, which is the sound of gas overflowing.

And Mentos let Coke form a "fountain", in fact, let carbon dioxide form bubbles, a large number of spills. But it's not easy to get carbon dioxide in soda to form bubbles. Because the formation of bubbles requires condensation of nodules, and in uniform water molecules, bubbles "squeeze" not out, need to overcome a lot of pressure to nucleate.

Bubbles also need to take the "elevator" to rise more easily. | | reference [2] |

But when you encounter some uneven materials, bubbles are easy to produce. For example, when you shake the cola and mix the gas in the water. Or insert a chopstick into the water, the uneven surface of the chopsticks is also easy to form bubbles.

Mentos has an uneven surface, with millions of cavities, so it also provides millions of nucleation sites for the gas, and the bubbles are like riding on an elevator and begin to rise and eject in droves. Based on this principle, scientists have explored several secrets to make the "Coke Fountain" spray higher:

An electron microscope photograph of Mentos's surface shows that the surface is uneven. | | Wiki |

1. Can you spray higher when you stand high? Standing in different places on the earth, the height of the Coke Fountain may be different.

In order to verify this problem, a group of coke fountain enthusiasts began to experiment, taking Coke and Mentos to different places to do experiments.

One group of researchers climbed Pike Peak in the United States with Coke, while the other group drove to California, Nevada and other places. All in all, the researchers visited the Coke fountain below sea level and more than 4000 meters above sea level, and recorded the height of the fountain.

Visible to the naked eye, the higher the altitude, the higher the spray. | | reference [1] |

And as they calculated, the higher the altitude, the higher the fountain.

This is because in the drink, only bubbles of a certain size can nucleate, and its minimum radius is r. The higher the atmospheric pressure, the greater the minimum radius r required for nucleation. The higher the altitude is and the smaller the air pressure is, the smaller the minimum radius r for nucleation is, and more bubbles will meet the nucleation requirements.

two。 Why does it have to be Coke and Mentos? With the development of this experiment, it is hard not to believe that this is the marketing method of Coke or Mentos. After all, according to the principle, any bubble water and uneven material on the surface can cause the bubble to spill out.

You can try making fountains with soda, Sprite or other drinks, or you can try putting other sweets, balls, or even sand in the soda. This could trigger a fountain. However, after repeated attempts, it is found that if you want to reach the highest level of the Coke fountain, then the best choice must be Diet Coke and Mentos.

The fountain height of some sparkling drinks is compared. It has to be Diet Coke! | | Wiki |

Diet Coke is also known as 0 Sugar Coke. There will be more aspartame in this Coke. The researchers believe that substances such as aspartame and benzoate may reduce the surface tension in water to a lesser extent, making bubbles easier to form. Other studies have shown that citric acid, sugar and other spices can also change the height of the fountain. It has been found that strawberry-flavored Mentos (containing citric acid) tend to produce higher fountains than mint-flavored Mentos (no citric acid).

All in all, the researchers found that 0 sugar drinks were sprayed higher than sugar. Due to the different additives between different beverages, there are also some slight differences in height.

As you can see, 0 sugar drinks are really sprayed higher. | | reference [2] |

People also made a comparison between Mentos and other sweets. According to some formulas, the average radius of the diameter of these nucleation sites is 5 microns, and the stomata above Mentos are just between this range. If the pores are smaller, bubbles also need some pressure to form.

Both the bubble size and the density of nucleation affect the height of the fountain, and Mentos coincidentally achieved the balance of these two requirements.

3. If you add more ingredients, you can spray higher? Since aspartame and benzoates can raise the height of the fountain, some people may think that aspartame drinks must be sprayed higher. But this is not the case, and the study observed that when aspartame dissolves to a mass ratio of 0.03%, the height of the fountain does not change.

The researchers also observed that a very small amount of artificial spices can significantly increase the height of the fountain, but the effect is also limited.

Look again, the fountain of the first item (pure soda) is the lowest. | | reference [2] |

To sum up, the various additives in the beverage seem to increase the height of the fountain to a certain extent, and no matter what is added, the foaming effect is better than pure soda. This simple experiment also has something to do with life: for example, there are complex solutes in sea water, so it is more likely to produce white foam than fresh water.

This could also explain why waves are more likely to produce white foam, the researchers said. | | Pixabay |

"this is so much fun." The researchers say. After all, who doesn't like the research that can strike a balance between games and academia, and drink cola casually?

When doing experiments, you should pay attention to safety and not face to face.

Image source: GIPHY

This article is from the official Wechat account: bring Science Home (ID:steamforkids), written by: Skin, revised by Shen Mengxi

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