Are you hot enough to make water bubble with just the heat from your touch?

What would you say if we told you that you could make water boil with nothing more than your touch? Impossible, right? There is no way that the human body (≈98.6ºF) could make water boil (≈212ºF). It just can’t happen. Well, you’re right, but the Homemade Hand Boiler is a fun trick that you can play on an unsuspecting friend or family member. You’ll even teach them a little bit about the properties of air, water, and molecules while you’re at it.

## Experiment

### 1

Fill a small, clear drinking glass nearly full with water.

### 2

Cover the top of the glass with a white handkerchief, or similar piece of cloth, and fix it in place with a rubber band.

### 3

Place your hand over the cloth and quickly turn the glass over so that the cloth is facing down and remove your hand. No water will come out! (For an entire experiment on why this works, see the Mysterious Water Suspension experiment.)

### 4

With the cloth still facing down, ask a friend to take two fingers and warm them up by rubbing them on their sleeve.

### 5

Ask your friend to hold their fingers beneath the cloth (they don’t even need to touch it).

### 6

While your friend’s fingers are below the cloth, push down on the glass with one hand while pulling up on the cloth with the other. The water inside of the cup will begin to boil!

## How Does It Work

When you first turn the glass upside down, you might expect the water to come flowing out, but surprisingly that isn’t the case. Although handkerchiefs and pieces of cloth are not waterproof, they seem to do the trick here. Handkerchiefs and pieces of cloth have tiny holes in them that should let the water through, but because of the molecular bonds of water, this doesn’t happen. The bound molecules of water create what is referred to as surface tension. If holes are small enough, the surface tension of the water is able to span the tiny holes, making the cloth nearly waterproof.

So what is making that water bubble? Bubbles are trapped air within a liquid, so that means that there is air entering the cup and the water. Although the surface tension of the water isn’t letting any water out,  air is getting in when you stretch the cloth. This is because molecules of air do not share the molecular bonds of water. Stretching the cloth pulls the holes in the cloth wider than normal and allows the air molecules to fill the little bit of space in the cup.

## Take It Further

Want to take the visual effects of the Homemade Hand Boiler even further? Put a few drops of food coloring in the water! Just make sure that you are using a piece of cloth that you don’t mind staining, as food coloring stains fabrics.