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I'm thinking of something similar to the liquid used in the classic dipping birds. Temperature differential in two "bulbs" at each end of a tube should cause vapor to expand and push liquid to the top, shifting the weight and tipping it. The closer to room temperature the boiling point is, the better. Thanks.

Devon Hansen
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    Dichloromethane – MaxW May 03 '19 at 14:56
  • Dichloromethane is a carcinogen and liver toxin (if this is for schools). If you want to be green, try "A dunking bird of the second kind". It just uses water and patience. Published in American Journal of Physics: https://aapt.scitation.org/doi/10.1119/1.1703543 – AChem May 03 '19 at 15:10
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    @M.Farooq It's suspected to be carcenogenic. And not very badly, because with its widespread use, one would know, otherwise. – Karl May 03 '19 at 19:11
  • Benzene is present in fuels, and it is a known human carcinogen. Widespread use does not guarantee safety (standards change all the time). If you talk to an old timer, they always say that they used benzene freely in labs. Not anymore. Organic chemists use DCM all the time and work with worse substances. Still they live very long or sometimes quite short. I would avoid volatile halogenated materials in general because they are quite bad for the liver even if they are suspected carcinogens. – AChem May 03 '19 at 21:52
  • Dichloromethane is surely toxic. While it can be acceptable for our columns I would not use it for demonstration aimed to general audience nor in a general class activity. – Alchimista May 04 '19 at 06:31
  • Toxicity is definitely a concern, as it should be. Plus it's a decent song. But long term my application may be industrial in nature, so certain safety precaution could be enforced. – Devon Hansen May 05 '19 at 03:10
  • @AChem Standards do not guarantee safety either. Ideally standards and safety point in somewhat similar directions, but there are plenty of times they are not the same at all. – Curt F. Sep 04 '22 at 17:09

2 Answers2

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Yes, there are lots. Start with Wikipedia's list of refrigerants; while it doesn't call out flammability, any fully-halogenated compounds will be effectively non-flammable. Trichlorofluoromethane has a standard boiling point just above standard room temperature.

You didn't say anything about pressure in your question. If you don't mind pressures higher than one standard atmosphere, and don't mind toxicity, candidates like ammonia, sulfur dioxide, and chlorine come into play. If you don't mind low pressure, you could even use water, although it might freeze as it boils off.

jeffB
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  • Don't forget bromine – A.K. May 03 '19 at 19:18
  • @A.K. He's the rugged guy in Lord of the Rings who gets shot up with arrows, right? – David Richerby May 03 '19 at 22:59
  • I suppose the higher the pressure the faster the whole sequence would progress, so lets says as high a pressure as is reasonable. – Devon Hansen May 05 '19 at 03:07
  • Can you tell us more about your safety constraints (flammability, pressure limits)? HFC-134a (1,1,1,2-Tetrafluoroethane) has a room-temperature vapor pressure between 4 and 5 atmospheres, maybe 25%-60% higher than the pressure in a full two-liter soda bottle. – jeffB May 05 '19 at 14:26
  • The higher the pressure the better. A higher pressure differential at as little of a temperature difference would be best. It should be able to hold at least 10 atm. Flammability isn't a huge concern. It will all be inside a sealed system. It's just a bit easier and safer to work with in general. – Devon Hansen May 09 '19 at 14:22
  • If you're looking for "general" safety, then a household/automotive refrigerant is probably your best bet. It looks like I was slightly off-base on 134a, its vapor pressure at room temp is about 6 atm. If this is a one-off and you aren't concerned about expense, other halocarbons let you dial in just about any boiling point or pressure you'd like. – jeffB May 09 '19 at 15:56
  • Probably a lot of general anesthetic gases like desflurane, isoflurane, and sevoflurane would also be worth a look. – Curt F. Sep 04 '22 at 17:28
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Most commercial refrigerants would work. There is a caveat, which is that they are usually also ozone depleting and are also greenhouse gasses with high , and the EPA will ream your bunghole if you handlGlobal Warming Potential (GWP)e them improperly. Almost all of these refrigerants are halogenated hydrocarbons (usually HFCs or CFCs).

One of the more modern refeigerants is R-1233zd (1-Chloro-3,3,3-trifluoropropene). R-1233zd is neither an HFC or a CFC, it is an HFO (hydrofluoro-olefin), It is safer to handle and more environmentally friendly than the former categories (zero ozone depletion and low GWP). However, it's also very expensive (~$50/lb), and you'll likely need an EPA 608 license to purchase it (though I may be mistaken here).

Update R-1233zd is actually flammable but only slightly, and it also has a very slow combustion rate of <10cm/s.

ThisGuyCantEven
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