Monday, October 24, 2011

Boiling Saltwater: Part Two!

I don't even know if the last post was that interesting, but it's got a second part now.  Oh well.

Another picture of water boiling (I don't know if there's salt in this one...).

So we know that adding salt to water increases its boiling point -- that is, the temperature at which water boils (which it cannot exceed in its liquid form).  Presumably, this would mean that raising the boiling point of water with salt would make it take longer to boil.

But this is not so!

Rather, salt water reaches a boil faster than an equal volume of regular water.  Oh, sweet counter-intuition.  Here's why:

There's this thing called specific heat, which is the amount of energy required to raise a certain amount of a certain substance by a certain temperature.  Typically it's one gram of something by one degree Celsius.  Water (H20) has a specific heat of 4.184 g/J*ºC, which means that it takes 4.184 Joules (a unit that measures energy) to raise the temperature of one gram of water by one degree Celsius.  Water has an unusually high specific heat compared to other common substances.

Dissolved salt (that is, sodium and chlorine ions) has a negligible specific heat compared to water.  This means that all the sodium and chloride ions heat up really quickly -- so quickly, in fact, that we can basically ignore the energy that they absorb.  Therefore, salt water consisting of 70% water and 30% salt will heat up approximately 30% faster than 100% water.  Pretty awesome.*

 *If you think stuff like that is awesome, anyway...


  1. But since you put only like 1promil of salt into water, it won't boil quicker at all :P

  2. This is the most random blog I have every come across haha.

  3. I wonder when you'll run out of salt related posts and end up writing about pepper.

  4. Is that why people add salt for boiling water? I thought it was because it was to add flavoring. ._.

  5. @Gizmo - You're right. It's probably not practical for cooking, really.

    @Mike - Maybe the subject is random, but the theme is always predictable.

    @Bersercules - NEVER!!!

    @DWei - I do believe that's probably a more practical reason. If you ask me, salt should always be added to everything for flavor.

  6. So, if you withdraw the salt, you can burn the water? :P

  7. You and me got salt in common!
    I love it!

  8. For cooking pasta in particular the reason you add salt to for flavoring the noodles, and has nothing to do with changing the temperature of the water. It requires a large amount of salt to change the speed to boil.


to prove that you're worth your salt.