Bill Gurstelle on Dippy Bird science

As a little kid, maybe five or six, one of my first remembered moments of heightened mechanical curiosity was over a Dippy Bird that somebody gave us. I have this very vivid memory of being utterly fascinated by it and wondering how it worked. The answer has been decades in coming. Here, MAKE Contributing Editor Bill Gurstelle, talks about Methylene Chloride, a plastic weld, and its use in powering Dippy Birds.

Methylene Chloride is the bonding agent I used to attach one piece of polycarbonate plastic to another piece when I was constructing the firepiston (see Feb 13 post in this blog.) MC works well because it’s thin and penetrates into seams well and does a good job of dissolving the plastic so it solvent welds together.

Coincidentally, I found out, while researching that methylene chloride is the same stuff used in the Dippy Birds to make them go up and down. The science of Dippy Birds, according to the How Stuff Works website, are this:

1. When water evaporates from the fuzz on the Dippy Bird’s head, the head is cooled.
2. The temperature decrease in the head condenses the methylene chloride vapor, decreasing the vapor pressure in the head relative to the vapor pressure in the abdomen.
3. The greater vapor pressure in the abdomen forces fluid up through the neck and into the head.
4. As fluid enters the head, it makes the Dippy Bird top-heavy.
5. The bird tips. Liquid travels to the head. The bottom of the tube is no longer submerged in liquid.
6. Vapor bubbles travel through the tube and into the head. Liquid drains from the head, displaced by the bubbles.
7. Fluid drains back into the abdomen, making the bird bottom-heavy.
8. The bird tips back up.

Methylene chloride is also used, apparently, in decaffeinating coffee. The MSDS says the stuff is somewhat dangerous, but apparently, not so much that it cannot be used in Dippy Bird toys – at least until someone complains.

Methylene Chloride and Dippy Bird Science

4 Responses to Bill Gurstelle on Dippy Bird science

Becky Stern on May 5th, 2009 at 2:03 pm said:

We learned to use MC in 3D design class in college; it’s excellent for building Plexiglas vitrines, and the syringe needle applicator bottle is just too fun. But we were warned to use it only in a well-ventilated area and, even then, not for very long. Kids came to class with many fewer brain cells, I’m sure, after waiting until the night before to make their projects, resulting in all-nighters in small dorm rooms with the stuff.

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Chet on May 5th, 2009 at 2:35 pm said:

I’ve been using this as a solvent in organic chemistry lab for two semesters, now; we’ve been referring to it by its IUPAC name “dichloromethane”. Among the uses noted above, it’s the substance in those bubbling Christmas lights. (I believe that it is dyed for Dippy Birds and Christmas lights; it’s normally colorless.) There’s a potential MacGyverism, if you needed to weld some plastic in a pinch.

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Anonymous on May 5th, 2009 at 3:25 pm said:

Most decaf is made with water (“Swiss water process”) now, though. No one wants the decaf made with solvent.

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Jack of Most Trades on May 5th, 2009 at 8:05 pm said:

2 years I spent working my way through school having to dance with that crap 5 mornings a week. It BURNS, BURNS it does… Leaves nasty welts on you and I’d hate to imagine what a splash in the eyes would have done.
It also defeats neoprene gloves, after about 2 hours my hands had this strange coldness about them and the gloves would get soft.

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