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Make fascinating bubbles which rather than floating on water actually sink.
Useful information
Kit List: 

A small transparent tank or a large clear bowl
Some washing up liquid
A wash bottle or a washing up liquid bottle


Description taken from Dave's Naked Scientist write-up:

What to Do

Add 3-4 tsp of salt into the wash bottle, or rather more into a washing up liquid bottle and then top it up with water.

Add some washing up liquid into the tank of water - probably 2-3 times stronger than normal washing up water.

Clear any bubbles from the top of the tank.

Drip the saltwater from the wash bottle onto the top of the tank from 5-10cm above and look at the bubbles being formed on the surface. Are they all the same?

Now do the same thing looking into the side of the tank, for a couple of hundred drops, does anything interesting appear?

What may Happen

On the top mostly you will produce normal drops, but sometimes you will see what look like bubbles but if you look closer they reflect light much better and they have far more momentum skittering across the surface.
If you look from the side you sometimes see bubbles which actually sink rather than float.

What is going on?

You are creating what are known as antibubbles. A conventional bubble is air surrounded by a thin film of water in air, an antibubble is the other way around, water surrounded by a thin film of air in water.
Both types of bubble are highly unstable in pure water because water molecules attract one another very strongly and try to minimise the surface area of the liquid. Detergent molecules have one end which is very attracted to water and a long oily tail which is repelled by it. so they cover the surface of the bubble stabilising it.

The air in an antibubble will cause it to float gently so they would be hard to tell from conventional bubbles. The salt weighs them down so they sink and you can tell the difference.

The antibubbles seem to form best when they are dropped onto water that is falling so the impact is less violent.

Risk Assessment
Date risk assesment last checked: 
Mon, 03/02/2020
Risk assesment checked by: 
Date risk assesment double checked: 
Mon, 03/02/2020
Risk assesment double-checked by: 
Beatrix Huissoon
Risk Assessment: 
Hazard Risk Affected Person(s) Likelihood Severity Overall Mitigation Likelihood Severity Overall
Liquids Slips and falls as a result of spillages. Electrical risks if the liquid spills on nearby electrical equipment. All 4 3 12 Clear up any spillage immediately. Ensure there are no electric components on ground near the experiment. Call first aider in case of injury. 2 3 6
Bubble mixture Damage to eyes as a result of contact with the mixture. Ingestion of the bubble mixture resulting in illness or allergic reaction. Public 4 3 12 Try to keep children under control. Demonstrator should show effect unless group are very calm and should take bottle away if child shows signs of getting excitable. Do not allow very young children to hold the bottle. Call a first aider in the event of an accident. If the salt mixture from the dropping bottle, or washing up water from tank, gets into an eye, demonstrator must call a first aider and may perform an eye wash if trained and confident to do so. If ingestion occurs, get victim to drink a glass of water. If liquid gets on skin, check about allergies. 2 3 6