by mixing / the mixture of potassium nitrate...

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elshan1980

Senior Member
Azerbaijani
Hi, everybody!

My question is about the following sentence taken from a reading passage about the history of ice cream:

Blasius Villafranca, a Spanish doctor living in Rome, found that by mixing potassium nitrate with snow and ice, the temperature would drop to the freezing point in no time.

I want to paraphrase the underlined phrase in a short sentence:

My opinion is: "The mixture of
potassium nitrate with snow and ice reduces the temperature to zero."

Is it correct? Or could you offer some possible and proper options?

Thanks in advance
 
  • Edinburgher

    Senior Member
    German/English bilingual
    No, I don't think your paraphrase is apt, because the idea of the sentence is that it is not the mixture (which would be the product you get after mixing the ingredients) but the act of mixing that causes the temperature to drop. You get an endothermic reaction when these things are mixed, but the chilling effect lasts only for a limited amount of time.

    You could say "The mixing of..."
     

    Myridon

    Senior Member
    English - US
    Reduces the temperature of what?
    The freezing point of the resulting brine is lower than the freezing point of water so you can transfer more heat into the ice/brine mix. There's no chemical reaction here.
    The temperature of the brine goes below 0 C so, no, your sentence is not correct.
     

    Edinburgher

    Senior Member
    German/English bilingual
    Reduces the temperature of what? Of the potassium nitrate and water, and therefore indirectly that of the container it's in, and from there that of anything on the outside of the container.

    While the resulting mixture does have a lower freezing point, that is not the issue. It is rather that the process of dissolving salt in water is endothermic (whether the fact that chemical bonds in the crystal lattice are broken makes the process count as a chemical reaction is moot; luckily I didn't actually say 'chemical', but perhaps I shouldn't have said 'reaction' either, and just called it a 'process').

    The initial experimental observation was that if you dissolve certain salts in (liquid) water (of any temperature), the water gets significantly colder (even if the salt starts out at the same temperature as the water), and the clever bit was to speculate (and subsequently to confirm) that if the water was already very cold (with all of it as snow and ice) before the salt was added, then adding the salt would reduce the container temperature even further, to below the freezing point of water, thereby supplying a source of 'coldness' that could be transferred to the cream (technically the "source of coldness" is a sink of heat, that can "suck" heat out of the cream).
     

    Myridon

    Senior Member
    English - US
    Regardless of how the process works (I still doubt that dissolving salt absorbs enough heat to freeze a container of cream), "the temperature of what?" and "the freezing point of what?" are important to the sentences. Each thing has a separate temperature and freezing point which generally not "zero". I hope that the freezing point of the container is higher than room temperature or the container will flow out the door. We shouldn't have to assume what is meant. To me, the original sentence sounds like the mixing changes the weather.
    Reducing the temperature of the ice cream mixture to 0C will not make good ice cream. You'll get some ice crystals with the other things separated out. It needs to be much colder.
     
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