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Q & A: Ice crackling in a beverage

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Most recent answer: 08/13/2016
How would you make ice that pops in the glass the way glacier ice does when a drink is poured over it.
- Aaron (age 35)
Springfield Mo

  I don't think there's anything special about "glacier ice" -- it should be very similar to any other kind of ice.

  Ice will crack when a room-temperature beverage is poured over it due to thermal stress.  Like other solids, ice shrinks when it gets colder, and expands when it is warmer.  If ice comes out of the freezer very cold and you pour a warm beverage over it, the outer layers of the ice will warm first and expand.  Heat takes time to conduct inside the ice, so the insides of the ice cubes won't expand.  The ice will crack under these circumstances because it is brittle and cannot change its geometry without breaking in pieces.

  The most sure-fire way to make crackly ice is to get it really cold, and to pour a hot beverage over it.  Don't make the ice cubes too small (ground up as fine as grains of sand would probably not generate a big enough strain to make big, noisy cracks -- snow doesn't make a lot of noise if you pour water on it).


(published on 10/22/2007)

Follow-Up #1: freezing bottles

What was said about the ice getting smaller as the temperature gets colder is true, but as the temperature falls ice first contracts and then expands, this is why a full plastic bottle left in a freezer for a long time will eventually burst.Right?
- Steven Groves (age 15)
Kington, Jamaica
The expansion which often bursts bottles occurs almost entirely in the conversion from liquid water to ice. There's a tiny bit of expansion also on cooling from 4C to 0C for pure water.

Mike W. 

(published on 10/22/2007)

Follow-Up #2: shattering ice cubes

Ice cubes made with filtered or spring water seem to shatter easier than ones from the tap water. Are the chemicals in the tap water acting as a binder, or are they interfering with the water crystallizing?
- Jane Murray (age 60+)

That sounds like an interesting observation and the second idea is a very plausible theory.  The salt in the tap water doesn't fit well in the ice crystal and wouldn't serve as a binder. Instead, the tap water ice cubes may have small pockets of concentrated salt water. These could make the ice a little less brittle.

The key question is whether the observation is correct. You could do an experiment comparing the shattering after dropping from different heights. One person should keep track of which type of ice cube is which and a different person should keep track of how they shatter. You may have to do many ice cubes to see if there's a consistent pattern.

Mike W.

(published on 07/26/2016)

Follow-Up #3: different types of ice cubes

The observations were made while cracking ice cube trays. The filtered/spring water cubes end up shattering where as the tap water cubes pop out fairly unscathed. So I thought perhaps the chemicals in the tap water were doing something to the crystallization of the water.
- Jane Murray (age 64)
Exton, PA, USA

That helps clarify the experiment a little. It's still possible that the tap-water froze with little liquid inclusions, making it less brittle, as you first guessed. Since the experiment involved knocking the ice out of the trays, not just dropping it and seeing if it shatters, I can imagine another possibility. The salty liquid from the tap water might form a thin outside layer, making it easier for the ice to break away from the tray. Again to test that you could try slightly different experiments. For example, you could try leaving the ice in the trays and dropping little controlled weights to see if it the two type shatter differently. Coins would work, but there would be some randomness depending on how they happened to land. Little metal spheres would be a good way to avoid that, so that any real differences in the ice would show up more clearly.

Mike W.

(published on 08/13/2016)

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