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I was linked to a Kickstarter for a cooling ball to be placed in drinks which claims with constant marketing hyperbole how much it relies on "Phase Change" ! which is a neat concept and seems not unreasonable, but in thinking about it I'm failing to imagine (as I'm no chemist, and of ill education) what refrigerant could be inside that meets the named requirements of non-toxic food safe, as well as passing from solid to liquid (or liquid to gas) such that a typical freezer would freeze it (−2 °C to −5 °C typically?), and it would liquefy around a temperature you'd want to keep your drink (say 1–3 °C).

Obviously water meets these requirements, however due to the expansion pressures water commits I have a very hard time imagining a small stainless steel ball containing that expansion through many freeze-thaw cycles without causing eventual deformities which would be continually weakened.

So the question is in the title, and to note the container is a sealed solid stainless steel ball of unknown thickness 2" in diameter.

Let me know if this question is off-topic, more than anything I'm just curious so I realize sometimes questions not based on a problem are poor fits for SE.

Do note: I am not interested in actually trying to do something with this, it is simply a curiosity, so don't be concerned if the things that come to mind aren't FDA tested, I'll settle for answers that simply show there are such things that are likely non-toxic regardless of thorough safety testing. Also the phase change from liquid to gas is a possible one too if you know of any safe chemicals here that wouldn't cause uncontrollable internal pressure and would have that phase change at the temperature range specified.

Just trying to come up with an idea for a compound that could meet their marketing hyperbole and finding I come up short.

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I tried to use the curated dataset from Mathematica to answer this question. You can ignore the following if you have no interest in Mathematica and just jump down to the end for my ideas.

The following code gets all of chemicals currently in the curated dataset and grabs the melting points and NFPA health rating. The second line finds the chemicals with melting points between -7 and 0 degrees and the last line looks for chemicals with a health rating of 0, which is low risk.

out = {#,  ChemicalData[#,"Name"], ChemicalData[#,"MeltingPoint"],
   ChemicalData[#,"NFPAHealthRating"])& ChemicalData[];
cull1 = Cases[out, x_ /; -7 < x[[3]] < 0];
cull2 = Cases[cull1, x_ /; x[[4]] == 0];

We go from about 43000 chemicals in the first list to 220 in the second and finally 6 in the last. I'm not sure I agree with the health ratings of these compounds but here you go (melting points in parentheses):

2-methyl-2-propanethiol (-0.5)

prehnitene (-6)

trans-1,2-dichlorocyclohexane (-6)

hexadecene (-6)

trans-1,2-dibromocyclohexane (-6)

olive oil (-6)

The only chemical I would deem "food safe" would be the last one. Perhaps some type of food-grade oil is the mystery substance.

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    $\begingroup$ Thanks!! This is exactly the sort of answer I was looking for. Olive oil would probably make a spectacular choice here with a -6C freezing point that should freeze in your average freezer and definitely keep your drink cold. No telling if this is what is used but it sure could be. Altogether bravo on the approach! $\endgroup$ – Jimmy Hoffa Aug 20 '13 at 19:58
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    $\begingroup$ You could even partially hydrogenate it to tune the melting point, if you wanted to. Mmmm, margarine cubes. $\endgroup$ – Aesin Aug 21 '13 at 21:51
  • $\begingroup$ Surprised that 2-methyl-2-propanethiol is down as non-hazardous...I would imagine it's pretty poisonous, although presumably less so than butanethiol. $\endgroup$ – J. LS Apr 26 '15 at 14:19
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    $\begingroup$ @J. LS en.wikipedia.org/wiki/Tert-Butylthiol - it stinks still terribly ;) $\endgroup$ – Mithoron Apr 26 '15 at 17:49
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Jimmy,

There are most likely many chemicals that have a melting point range in that vicinity, but I can't comment on their toxicity. However, I can comment on some of the science here.

First of all, water is one of very few molecules that expands when it freezes. That has to do with the hydrogen bond network formed between water molecules in the solid state. This network is slightly less dense than low-temperature liquid water, so water will expand when it is frozen. (This is also why solid water floats on liquid water.) Most compounds form frozen solids that are more dense than their liquid state, so they will contract on freezing. This is why it is fine to freeze these metal balls if they are filled with something besides water. Although they could have water inside, but just not be completely full, I suppose.

If you were going to find a water substitute, then you would want to find a chemical that has a high heat capacity and enthalpy of fusion. Heat capacity is the amount of energy required to heat a given substance by a certain temperature. If a substance has a high heat capacity, then it take more energy to change the temperature of that material. (It gets this energy by removing heat from your beverage.) The enthalpy of fusion is the amount of energy it takes to change a substance from a solid to a liquid. Again, you would want something with a high enthalpy of fusion for the same reasons as for heat capacity. Unfortunately, water is really great on both of these fronts, which is why ice cubes are so great for cooling a drink.

I'm not sure I really answered your question, but I hope that helps a little.

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http://en.wikipedia.org/wiki/Glycerol has a melting point of 20°c (in comparison to water's melting point +20°c) and it is used as ingredient in 'Bounty' sweets (E number : E422)

I also suggest that you have a look at the E-number list. There are a lot of allowed products for human consumption (however not all are safe in high doses) you can find the list here : http://en.wikipedia.org/wiki/E_number

An exact answer to the question I don't have :(

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