Fountain in a flask

Use a candle to power a fountain!

5 minutes



  • Put on protective gloves and eyewear.
  • Remove protective gloves before lighting the candle (step 2).
  • Conduct the experiment on the plastic tray.
  • Keep a bowl of water nearby while working with fire.
  • Keep flammable materials and hair away from the setup.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

I added more than two drops of chlorophyllin. What should I do?

Don't worry — just continue the experiment!

The candle goes out when I put the flask on the stopper.

This step should be done very quickly and carefully. If you touch the candle or spend a long time fixing the flask, the candle can go out. Try again – you can do it!

And remember, you can always ask an adult for help.

I’m having little to no success making the “fountain.” What should I do?

Make sure that the stopper is inserted deep enough into the flask. Also, check that the candle is lit. Repeat the experiment, paying particular attention to these details.

If I want to repeat the experiment, do I really have to rinse the flask with the solution?

Any remaining combustion products will keep your candle from burning. If you try to repeat the experiment immediately, it’s very unlikely you’ll get the result you want. That's why we advise that you first rinse the flask with the solution or water.

I want to repeat the experiment, but the candle isn’t lighting!

This can happen if some of the solution got on the candle. Use a napkin to pat the candle dry. Or take another candle from the set.

Step-by-step instructions

Dye some water.


Light a candle. The candle is made of paraffin. Paraffins are long chains molecules made of carbon atoms with some hydrogen atom attached. Paraffins are good at reacting with oxygen with a release of heat and light. In other words, they are good at burning. When they burn, their carbon and hydrogen atoms combine with oxygen and turn into water and carbon dioxide gas.


Watch the dyed water rush into the flask. Why does this happen?


To repeat the experiment, you need to remove the carbon dioxide gas from the flask and fill it with fresh air. The easiest way to do it is to fill the flask with water and then empty it.



Dispose of solid waste together with household garbage. Pour solutions down the sink and wash with an excess of water.

Scientific description

One interesting side effect of the reaction between paraffin  and oxygen is that for every two molecules of oxygen gas  ↑, only one molecule of carbon dioxide gas  ↑ is produced. As a result, the total amount of gas and thus pressure are decreased. Usually you don't notice this change when you burn a candle. However, when you do it in a flask, the pressure only drops inside the flask, making the flask draw water from the beaker. The water passing through the thin tube makes a nice fountain.

What other factors contribute to the fountain phenomenon?

While this fountain is mostly caused by the combustion of oxygen, a few other factors also contribute to the cool phenomenon you just witnessed. In addition to the reduction in gas volume during the combustion process, the resulting carbon dioxide CO2 also partially dissolves in the water, and almost all of the water vapor condenses. This adds to a general decrease in the volume of gas inside the flask.

The heat that is released as the candle burns also contributes to the fountain’s formation. When the candle burns, the air in the flask heats up and expands. After the candle goes out, the gases cool and contract. Thus, the number of gas molecules decreases, the temperature decreases, and consequently the pressure inside the flask decreases. And as a result, water is pulled into the flask to make a fountain! This fountain will continue until the gas pressure inside the flask is balanced.

How is a candle flame structured?

Usually, a candle flame is divided into three zones:

  1. The inner zone is the coldest and least luminous. This zone is mainly comprised of unburnt paraffin vapors.

  2. The middle zone consists of incandescent fuel particles. This part has a higher temperature and it is yellow and orange in color.

  3. The blue outer zone is where complete combustion takes place. It is the hottest section of the flame.

That’s interesting!

Geysers in nature

Have you ever heard of a phenomenon where boiling water and steam burst out of the earth in violent eruptions? Scientists suggest that the vents where this occurs, known as geysers, stem from underground channels and caves filled with groundwater. Molten rock or magma heats the water from underneath, and the water gradually boils, but not evenly — at its deepest point, it becomes quite overheated. As the pressure increases, some of the water is pushed violently to the surface. Some eruptions last only a few minutes, while others can last hours or even days! This process will continue until all the water is forced out or until the temperature inside the geyser decreases.

The name of this phenomenon comes from the famous Great Geysir in southwestern Iceland. Its name is derived from the Icelandic verb meaning ‘to gush.’

Most active geysers are found in one of five countries: Iceland, Chile, New Zealand, Russia, and the US. But half of all known geysers are located in Yellowstone National Park in the US. One of the most famous is “Old Faithful,” which erupts approximately every 90 minutes with a jet of water up to 30–55 meters high!