15
Sep
10

Better (or Stranger) Refreshments With Zone Refining

Friends, I always manage to do this by accident. You, having psychological and gustatory urges which I can only imagine, may find that you will want to do this same thing intentionally. -This- is zone refining.

You may already know that, if water is chilled very slowly and uniformly, it may freeze uniformly, suddenly and thoroughly. The freezing point is very precise. It is also different for other substances. Mixtures of substances which freeze differently – such as water & sugar, or water & food coloring, or water & carbon dioxide – will not freeze uniformly. Such mixtures can *un-mix*.

The first time I saw this un-mixing was a delightful surprise. It was delightful because it was unexpected and because I recognized it immediately. The venerable Scientific American magazine had taught me about the phenomenon of zone refining.

I had been eager to chill a bottle of Manischewitz wine, one day during college. I put in in the hall freezer in the Alley 5 kitchenette of Ruddock House. Then I forgot about it.

No, I didn’t really forget about it. I merely remembered it later than I had intended to remember it. It was a stunning sight – a 3/4 full squarish bottle which now had a fairly clear chunk of ice perched over a much smaller amount of concentrated wine. My exclamations brought a few Trolls to the kitchenette doorway. They were happy for me. There was some discussion of the potential of the liquid to offer an enhanced drinking experience.

That discussion, as dorm discussions with random Trolls often do, diverged toward other subjects. ‘Stud‘ offered his opinion that “Three quarters of a lethal dose of anything is a great high.” My retort – that three quarters of a lethal dose of concrete would be really hard to keep lit for smoking – was met with Stud’s expert correction: “You don’t smoke concrete, dummy – you shoot it up.”

Most recently, I did it again with half a bottle of Pepsi. Vitamin P keeps me going, as it did during performances of Stone’s Throw Dinner TheaterOklahoma!‘. It needed some fast chilling one night, and a preoccupation with my role resulted in a chunk of ice and Pepsi syrup. Yum!

Freezing doesn’t strictly require a colder temperature than for liquid. Either (depending upon pressure) can exist at a phase-transition temperature. When a liquid mixture is cooled slowly, it will cool even more slowly at this phase transition. The movement of heat that is cooling serves to make liquid become solid, leaving no extra movement of heat to lower the temperature. Take a look at this phase diagram for water. The ‘mp‘ dot is the melting point (freezing point) that we usually think of – normal pressure, 1 atmosphere. ‘mp’ belongs to both liquid and solid.

Various substances have very different phase diagrams. Here’s Uranium Hexafluoride, the form of uranium that is convenient to use in processing nuclear reactor and weapons fuel. (I would offer a phase diagram for Pepsi syrup, but it doesn’t seem to be available.)

A liquid mixture will have its minute constituents freezing at their individual ‘mp’s. For Pepsi, water freezes at a higher temperature than (prior to) the syrup, which has sugar, flavoring, and coloring. The very transition of water from liquid to solid prevents (temporarily) the temperature from getting low enough to freeze the syrup.

This stuff has seemed understandable to me for over 40 years. I do wonder about one thing – can I circumvent laws regulating the distillation of alcohol by using zone refining (of Manischewitz wine, no less!) instead of differential vaporization (a ‘still’)? Do I need to alert regulators to this potential loophole?

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1 Response to “Better (or Stranger) Refreshments With Zone Refining”


  1. September 15, 2010 at 9:00 am

    Jim Too,

    I too feel a sense of wonderment for the non-intuitive nature of nature, and water is indeed among the most wonderful of all stuff. You remind me that water, except for ammonia, has the highest specific heat capacity of all known substances, and this makes it an ideal heat sink for global warming. Without this property we humans would likely be toast, or more likely, not be here at all.

    Then there is the latent heat of fusion, necessary to understanding how ice keeps scotch cold and why air temperature stabilizes as snow melts. Ice requires thermal energy to form and to melt while temperature stays the same.

    Another property of water is also odd, making it different from almost any other liquid: the fact that its density decreases when it freezes. Ergo, it floats. If water acted like other stuff, ice would sink and life on earth would be impossible. I attribute this to the anthropic principle. In however many other universes there might be with rules of physics that are different from ours in this respect there would be no life to observe the absence of bergs.

    Our corner of existence with its fluky laws does fine and we are here because the laws are right. The laws are not right because we are here. At least that’s the way my mind works.

    Thanks for the neuronal exercise.

    Jim one


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