Substances with near room temp phase change

Glacial is a good idea. It definitely works in the UK if it's left in a garage. It's like opening an advent calendar wondering what state it'll be in. Different masses (in any of these examples) will provide differing amounts of lag, with larger values giving a general trend over the days, rather than the immediate temperature.

Caesium. Not particularly safe or easy to get, but MP is 28C.

I've been making a fair bit of diethyl ether recently (BP 34), likely contaminated with dimethyl ether (BP -27?C) and methyl ethyl ether (BP -8?C). With the lower boiling ethers in there, it keeps popping the stoppers off the flasks I put it in, so I opted for a balloon in the meantime, which humorously erects or goes flaccid based on the room temperature.

Maybe a balanced composition of ethers, with a smiley face drawn on the balloon, could indicated STP.

Honey, butter and chocolate*** are infamous for going from solid to liquid and back over a relatively narrow range for a natural product. I expect an interesting sweep of temperatures could be achieved merely by mixing those together (diary cream?). Some cooking oils will solidify if left in the fridge; which I have seen a student do, thinking it belonged there (they had servants at home, literally). A benefit of using something like honey or chocolate is that their epic sugar content and dryness means they effectively never go off; archaeologists have found still edible honey buried in a tomb in Egypt, put there thousands of years ago. Honey also has the nice property of going from transparent to opaque depending on the state. It'd be good if you had something like an hourglass that turned it's self over each day.

There are probably combinations of wax (mixed with oils) that will also work at room temperature. Google around 'freezing point depression', 'boiling point elevation' and 'eutectic'. Unfortunately, many of the examples will be solely water / salt, but that would still be useful for winter.

One place to start could be with Phase Change grease used on computer CPUs.

-Thermoscope

I realise you were after state changes, but on a related note: Galileo's thermometer



***The melting point of chocolate and it's solidification is one of the hardest parts of making it. It needs a great deal of time in conching mills (like paint) to grind it as smooth as possible. If it cools incorrectly, it comes out like grit. This US documentary from the ?late 70s?/ ?early 80s? provides an excellent overview of the entire process: 'The Great American Chocolate Factory'.

[Edited on 28-3-2012 by peach]

Was that a case of "great minds think alike" or rather "fools seldom differ".