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I was recently looking at a Wurlitzer juke box, and noticed something strange. It's decorated with liquid-filled tubes. Gas bubbles are injected at the bottoms of the tubes, and the bubbles naturally rise.

What was strange was that, as the bubbles rise, they shrink! Not just a little bit, but very noticeably. At first I assumed it was some kind of optical illusion, but actually many bubbles shrink down to nothing and disappear. How can this be? Where does the gas go? Surely it can't be dissolving into the liquid. It can't happen that fast, and the liquid would be saturated by now.

Wurlitzer bubbles disappearing

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I don't know the physics, but the tube is heated not by a light bulb as stated above, but by a resistor at the base of the tube that transfers heat to a small copper tube holder that the bottom of the glass tube fits into. It doesn't take a lot of heat to get the tubes to bubble. If you place your hand around the bottom of the tube, it will start bubbling. –  user60577 Oct 6 '14 at 18:37

3 Answers 3

up vote 15 down vote accepted

Here is an explanation by Bo Danforth:

Shown in the picture above is a segment of a Wurlitzer jukebox bubble tube. In the tube, the bubbles rise as expected, but as they approach the top, odd things begin to occur. Instead of remaining the same size as one might think, or increasing slightly from a minute reduction in pressure, they instead decrease in size, in some cases disappearing entirely. The reason for this bewildering sight is that the bubbles do not actually contain air, but are pockets of heated vapor. The bubble tube is a sealed system where the air has been completely removed by a pump, creating a partial vacuum, which causes the liquid to fill the remaining space with vapor. The system is at a pressure where it will change states near room temperature. When this sealed tube is placed next to a heat source at the bottom (the light bulb) the liquid near it reaches a boiling point, according to the equation of PV=NRT. As the bubbles of vapor float upwards along the exposed glass and away from the heat source, they slowly shrink as the gas cools down, condensing back into a liquid state.

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A great explanation. How did you find it? I spend ages Googling before I came here. –  Rocketmagnet Dec 29 '11 at 21:41
I think I used the following Google search: "Wurlitzer jukebox" bubbles liquid. –  Qmechanic Dec 29 '11 at 22:03
The liquid used is Dichloromethane (a.k.a Methylene chloride) because it is very volatile, non-flammable and relatively harmless if accidentally released. –  Philip Gibbs - inactive Oct 6 '14 at 20:37

Either this gas is dissolved, or it is a vapour of that liquid that condenses gradually.

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+1 for vapor... –  Vineet Menon Dec 28 '11 at 10:46

The fluid in the tube is not water as some might think but an organic solvent called Dichloromethane. The reason the bubbles form is due to the fact that the fluid is heated at the base of the tube to it's boiling point which is a low 103.3 F degrees. You can almost get it boiling by holding it in your hand. The bubble is actually the vapor form of the liquid, as the liquid travels up the tube it cools and returns to the liquid state.

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protected by Qmechanic Jul 31 at 18:41

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