Whisky Stones and Physics

Recently, for no real reason, I decided to buy myself some whisky stones.  These are little cubes of rock which you put in the freezer before adding them to a drink (usually alcoholic) which you want to be chilled.  The advantage over ice is that the rocks do not melt and dilute your expensive whisky (not that I drink that).  I have used them a few times and was quite disappointed to discover they don’t cool a drink very well at all, at least compared to ice.  The best they’ll do is stop it getting any warmer, but they are no substitute for ice cubes.  Now I’ve thought about it, I should have figured out why: a drink is cooled mainly by the process of ice cubes melting rather than their being cold, and I learned all about this in physics class at school.

There is a physics term called Specific Latent Heat which is defined as the amount of heat energy required to change the phase of a substance, i.e. turn it from a solid to a liquid, or a liquid to a gas.  This amount of heat is usually a hell of a lot more than that required simply to increase the substance’s temperature, and I remember my physics teacher telling us why you feel so cold when you step out of a shower: the heat taken from your body to evapourate the water is 2,265kJ per kg (which is, of course, why we have evolved to sweat to cool us down).  He also gave us an example of the effect in reverse: burns from steam are so much worse than those from boiling water because that 2,265kJ per kg is being transferred from the water onto the skin.

I remembered this reverse effect when I was in Sakhalin, and I noticed that the air temperature dropped right down when the snow on the ground was starting to melt.  Of course it would, because to change snow into water takes 334kJ/kg heat energy out of the air.  But somehow I’d forgotten this when I ordered the whisky stones and expected them to work like ice cubes.  My old physics teacher, wherever he may be now, would have given me a right bollocking for this.

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13 thoughts on “Whisky Stones and Physics

  1. My Melbourne home has an evaporative air conditioning system, its very comfortable, open windows are encouraged and its fairly low cost compared to refrigerant cooling.

  2. Professor Joseph Black (of the Universities of Glasgow and Edinburgh) is the chap who sorted this out. James Watt worked with him for a while.

    As they must have told you at school.

  3. @ Bardon,

    Interesting! Does that work in Melbourne because of the cooler climate, or could it work in QLD too? A pal of mine reckons he’s onto something with some innovative new AC system, I wonder if he hasn’t stumbled across the same idea?

  4. As they must have told you at school.

    Alas, no. James Watt we learned about yes, as we did about pretty much everyone who had a unit named after them (my favourite character by far was Nikola Tesla). But this was outside the syllabus, it was just my physics teacher – a splendid chap who deserves a post of his own – who gave us the background to a lot of the concepts and the scientists involved.

  5. It works very well in Melbourne due to the relatively lower air humidity and not in Queensland because of the higher humidity sub tropical climate, its the difference between the dry bulb and the wet bulb temperature of the ambient air that indicates whether evaporative air conditioning is a goer. As for ambient temperature, evaporative works in high temperatures as well, provided the air is dry but it cannot drop the temperature as much as refrigerant AC can hence refrigerant is normally a better solution in very hot dry locations in this day and age of development. Historically evaporative AC was used in hot dry areas.

  6. Ice stones are rubbish, and a little melting in the Laphroaig isn’t going to make that much difference

    I used them with Jack Daniels! 😀

  7. @ Bardon,

    Interesting stuff…obviously being a Brit I don’t know a lot about AC. For you guys in QLD it’s probably the first thing installed in a house after the toilet.

  8. @ PeteC,

    They do look good! Although I’m not sure I could sit drinking whisky with pink ice cubes… :-/

  9. Ice? In whisky? Gah.
    Reap what you sow, and all that. Forget about the ice, just enjoy the stuff.
    (with a drop of water if required)

  10. Used to be a luxury and was frowned upon by the diehards, raised houses, shaded verandas, tree cover, use of the suns aspect and ceiling fans were the norm not that long ago. I strated off without it sued to jam ice packs up against my water bed bladder on a hot night, only started with split systems much later on in life. Now reverse cycle AC everywhere, I have a ducted system throughout the house, nice for a touch of heat in the brisk winter morning as well. The compressor from my ducted system makes the street lights flicker when I fire it up.

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