On Mon, 19 Nov 2007 10:02:34 -0800 (PST),
[email protected]
wrote:
>On Nov 18, 5:36 pm, Crescentius Vespasianus <[email protected]>
>wrote:
>> If the water in your water bottles
>> freeze into a block of ice, you have the
>> wrong water bottles. Get some Polar
>> water bottles, boil some water right
>> before you go out the door, and pour
>> into the Polar. Then you won't be
>> sucking on a block of ice, when you get
>> thirsty. Now for coke cans exploding in
>> the wedge pack, under the seat, due to
>> freezing, and easy solution is to throw
>> a chemical heat pad in their with the
>> cokes, and they won't blow up and make
>> such a mess in there.
>
>adding some salt to the mix helps in two ways, does not freeze as fast
>and helps preventing cramps!
>carlos
>www.bikingthings.com
Dear Carlos,
In terms of freezing, the effect of adding a little salt to a rider's
water bottle is mostly wishful thinking.
Salt does indeed lower the freezing temperature of water, but lowering
the freezing point significantly takes a lot more salt than the pinch
or two that we can tolerate in drinking water.
How much salt can we tolerate? Back when stokers shoveled coal into
steamship furnaces, drinking water was mixed with sea water at a 10-1
ratio to help the hot, sweaty stokers avoid cramps.
Sea water is undrinkable, with only about 35 parts salt to 1,000 parts
water.
All that salt lowers the freezing point only from 32F to 28F.
(Admittedly, freezing salt water is trickier than it looks, since the
frozen water ends up with a much lower salt content. In experiments
using containers smaller than the Atlantic Ocean, the salt content of
the remaining water rises as ice forms on top, lowering the freezing
point slightly as more water is frozen.)
For a more practical example, consider making making ice cream. To
lower the freezing point enough for the external freezing mixture to
make ice cream, you add half a cup of salt or more to two cups of ice
(about 250 ppt) and use it to cool the separate cream mixture:
http://chemistry.about.com/cs/howtos/a/aa020404a.htm
Cooks often make the same mistake about salt raising the boiling point
of water, expecting a dash of salt will raise the boiling point of a
gallon or two of water and cook noodles in record time.
Alas, a dash of salt raises the boiling point of the water less than
the margin of error on a kitchen thermometer:
http://www.newton.dep.anl.gov/askasci/gen01/gen01021.htm
About 0.5C per 58g salt per kg water is the figure mentioned above.
Sea water is only 35g salt per kg water. You'd need about 250 grams of
salt to raise the temperature of 4 quarts of water in a small boiling
pot from 212F to 213F. (Ordinary medium-grain table salt is about 70
grams per quarter cup, so you can toss in almost a cup of salt and get
only a tiny effect.)
Again, the matter is more complicated than expected, since the water
from most faucets is hardly pure and the altitude of the kitchen has
more effect than salt a cook is is likely to dump into the pot.
To return to salt and freezing water, the fish industry uses brine for
cooling fish. Here's a pdf with a nice table showing how much salt (by
weight) is needed to lower the freezing point:
http://seagrant.oregonstate.edu/sgpubs/onlinepubs/h99002.pdf
As you can see, adding salt to the water doesn't lower the freezing
point noticeably until you
The lowest point that can be achieved by adding salt is technically
about -6F, but Fahrenheit used sal ammoniac, not NaCL, and then
sea-salt, which isn't pure NaCl, when creating his 0-32-212 scale:
http://antoine.frostburg.edu/chem/senese/101/measurement/faq/zero-fahrenheit.shtml
Cheers,
Carl Fogel