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Firstly I am not a chemist so please be kind. I am a creative technologist working on a large art installation. The challenge is to make people perceive rain without it raining. I am looking for something we can very occasionally drop from above that will feel like a rain drop but almost instantly evaporate leaving the person completely dry when they leave (they will only experience a few drops whilst in the room — the rest of the effect uses lights and sound).

My initial thought was liquid nitrogen but I assume that whilst a tiny occasional drop on the back of the hand would be fine, one in the eye for example would probably be dangerous. Plus the room would need to be heavily ventilated to prevent the risk of asphyxiation.

I'm assuming the answer is nope but if anyone has a genius idea for some way i could achieve this effect I would love to hear it. Over to you.

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    $\begingroup$ Um, how about, well, water? $\endgroup$ – Curt F. Dec 13 '16 at 13:55
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I'm assuming the answer is nope but if anyone has a genius idea for some way i could achieve this effect I would love to hear it.

Nope ;-)

Your concerns are justified and I wouldn't expose the audience to anything but water either.

you can

  • use water from all above
    • and let the audience get wet
    • and hand out rain coats

  • use water and only let it rain to the left and right of a marked path or

  • apply a more sophisticated technique, as used by the random international art studio in their rain room. Here, it rains thoughout a whole room, but the visitors are tracked by cameras and whereever they move, the water is selectively switched off.

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If you really don’t want to use water as suggested by Klaus but absolutely want to do this in exactly that way, the next-best alternative is probably diethyl ether. It evaporates really quickly ($\vartheta_\mathrm{b} \approx 35~\mathrm{^\circ C}$) and has been used in the past as anaesthetic. However, you would still need to keep the room well vented to prevent suffocation in the long run, and you need to enforce a really strict anti-smoking, anti-flame policy.

All things considered, if it is only the occasional drop I would definitely use water.

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    $\begingroup$ I would guess some of the Freons would be a good choice. The boiling point and vapor pressure of say isoflurane is 45 C, and it is at least as non-toxic as diethyl ether. It is far less flammable too. But toxicity and asphyxiation risks would still be present. It is also a horrible greenhouse gas. $\endgroup$ – Curt F. Dec 14 '16 at 1:45
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If it's only a few drops, why not use water? It would dry quickly in a warm room.

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You can look into Galden Fluid, such as HT70 or HT55. It's priced around $800 a gallon so if money is a concern, look elsewhere.

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    $\begingroup$ Almost all variants of these fluids are known skin irritants and should not be inhaled. I would not recommend any of these for a water substitute. $\endgroup$ – Todd Minehardt Aug 27 at 18:45

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