larry@grkermit.UUCP (Larry Kolodney) (08/11/83)
I've always been under the impression that when boiling water, you
should put cold water from the tap into the pot. Is there any reason
not to use hot water from the tap? Is this just a manifestation of my
puritan backround?
-larry
--
Larry Kolodney
{linus decvax}!genrad!grkermit!larry
(ARPA) rms.g.lkk@mit-aistanwyck@ihuxr.UUCP (08/12/83)
I don't know, but it sounds faintly like my mother-in-laws insistance that putting hot-water (the hotter the better) in ice-cube trays causes them to freeze faster. The only thing I have noticed about hot-water in the freezer is that it makes for more frost to defrost..... D. Stanwyck ..!ihnp4!ihuxr!stanwyck @ bell labs, naperville, il
halle1@houxz.UUCP (08/12/83)
Believe it or not, there is a valid reason for using cold tap water. If all you're going to do is boil noodles or steam vegetables or something like that, use hot water and save energy (maybe $.0001) and time. However, if you are going to drink it, such as in coffee or tea, use cold. There seems to be more air dissolved in cold water which stays in when boiled in a kettle. This makes the beverage "livlier", while hot water makes it "flat".
heretyk@abnjh.UUCP (S. Heretyk) (08/12/83)
Water gathers bacteria in the hot water tank so one should always use cold when cooking. Shelley Heretyk
asente@decwrl.UUCP (Paul Asente) (08/14/83)
Hot water does NOT pick up more bacteria in the water tank; it is perfectly safe to cook with. It does, however, tend to pick up more trace elements from the pipes and the inside of the water heater. Some people claim that this makes coffee and tea taste different, so you should always use cold water for these. Using hot water to cook vegetables, pasta, and such is more energy-efficient (the water heater always has the water hot) and, possibly more important, is much faster. Remember the old story about hot water freezing faster than cold? I once read a long article on this which claimed that the source of the story is ice cream making. Starting with a hot mix rather than a cold one is faster for freezing ice cream since the hot mix melts the ice faster making an ice water bath rather than just ice; you can achieve the same effect by adding water to the ice. Don't do it though; it makes the ice cream grainier (same thing happens if you use too much salt). Bringing you better living through thermodynamics, -paul asente (decvax,ucbvax,allegra)!decwrl!asente
smb@ulysses.UUCP (08/14/83)
If you're planning on using the water for cooking, by all means use cold water. The hot water will contain more dissolved minerals from the tank and pipes, which will noticeably affect the taste.
smb@ulysses.UUCP (08/15/83)
Actually, hot water may actually freeze faster. There was an column on the subject in the Amateur Scientist section of Scientific American; I'd cite a more exact reference, but I just moved....
tll@druxu.UUCP (08/15/83)
Yes, hot water DOES freeze faster than cold water! But only if there is a layer of frost under the ice cube tray. The hot water melts the frost onto the bottom of the tray, thus improving heat conduction. Tom Laidig
prgclb@ihuxm.UUCP (08/15/83)
All other conditions being equal, an ice cube tray
filled with hot water would freeze faster than
a tray filled with cold water.
It takes heat to evaporate water, so unless an
external heat source is applied (such as using a stove
to boil a teakettle full of water), the heat comes from the
liquid itself. Loss of this "heat of vaporization"
results in a lower temperature for the remaining liquid.
(I'm sure you've all experienced this principle
at the doctor's office -- you get swabbed with disinfectant alcohol
before getting stuck with a syringe -- the alcohol evaporates quickly,
taking the heat of vaporization from your skin, leaving your skin cold.)
Hot water will evaporate faster than cold water,
resulting in more heat of vaporizaton loss,
resulting in faster temperature loss in the liquid.
Cold water, on the other hand, will evaporate very
little, and therefore has to lose its most of its heat
(and temperature) through radiation and convection,
both slower processes.
>From the armchair chemist . . .
Carl Blesch
Bell Labs - Naperville, Ill.
IH 2A-159, (312) 979-3360
ihuxm!prgclbhalle1@houxz.UUCP (08/16/83)
The reason that hot water evaporates faster is that it takes less energy to raise the temperature of the molecules to that needed to evaporate. At typical tap water temperatures, and even at very hot temperatures, the increase in evaporation is negligible. The additional heat extracted by evaporation is less, probably very much so, than the additional heat content of the water due to the higher temperature. Consequently, hot water will NOT freeze faster. One possible exception is if the container has a broad surface and the volume of water is very small. In this case, the evaporation might be large enough to have an effect. In the general case, however, cold freezes first.
asente@decwrl.UUCP (Paul Asente) (08/16/83)
Sigh. It's true that hot water loses its heat faster than cold water, so in some sense it does "freeze faster" (it loses more heat in the same amount of time than cold water does). Eventually, however, it becomes cold water from losing the heat, and then has to freeze the way cold water does. Therefore it takes longer. If you don't believe this, there is one sure way of deciding. Fill one ice cube tray with hot water, one with cold, put them both in the freezer and check each one every five minutes until they're frozen. -paul asente (allegra, decvax, ucbvax)!decwrl!asente
wisen@inmet.UUCP (08/16/83)
#R:grkermit:-55800:inmet:6400040:000:674 inmet!wisen Aug 15 11:21:00 1983 Water from the water heater tends to have rust and other impurities. While waiting for you to take a shower, the water in the heater bides its time by corroding the tank it is held in. Speaking of which, it is an efficient idea to flush rust particles from your heater every few months by opening the heater's bottom outlet valve [plumbers probably know the correct term for this faucet-like protuberance] and allowing the water to stream out, taking rust particles with it. Without giving your heater this occasional enema, the layer of rust particles may build up enuf to act as an insulator between your burner flame and the water. --------------Bruce Wisentaner
larry@grkermit.UUCP (Larry Kolodney) (08/16/83)
prgclb@ihuxm claims that because there is a greater latent heat loss,
hot water freezes faster. I don't think this makes any sense. It may
be true that hot water losses its heat faster than cold water, for the
reason given. But by the time it reaches the temperature of the cold
water, it will have THE SAME rate of evaporation. Thus, it first has
to reach the temp. of the cold water and then freeze as quickly as the
cold water normally would. DOES THIS MAKE SENSE?
--
Larry Kolodney
{linus decvax}!genrad!grkermit!larry
(ARPA) rms.g.lkk@mit-aijcz@ncsu.UUCP (08/16/83)
References: grkermit.558 Water from the hot tap contains minerals and other stuff that collects in the hot water heater tank. So, hot tap water is not to good to drink or cook with, especially if you have an old hot water heater. New hot water heaters may not have the problem. Run a glass of hot water, let it cool, then compare its taste to a glass of cold water. --jcz
jlgray@ixn5c.UUCP (08/16/83)
One possible reason that hot water might "freeze" faster than cold water is that under the proper conditions they may differ in their transision through the "supercooled" state. Water that has been boiled for a time may have a higher density of impurities (particulate matter) which can cause ice crystals to form immediately as the water temperature falls below 0 C. Pure water, on the other hand, may remain in the liquid state until about -2 or -3 degrees C. If you have a freezer which is set only a few degrees below 0, pure water may not freeze until you touch it. I've actually seen this. Freezing hot or cold, Jerry the weasel. ixn5c!jlgray
ajy@hou2b.UUCP (08/16/83)
In my home town, the local indoor hockey rink was owned by the father of a friend of mine. This friend told me that they used hot water when making ice on the rink. Not only did it freeze faster (niether of us knew the physics) but the water had less air in it. Thus, the ice was clearer and free from bubbles which, I suppose, is important for hockey rinks.
levy@princeton.UUCP (08/17/83)
The same reason (cold water contains more air than hot water) can explain why
cold water (sometimes) freezes faster. If you have boiled your water previously
and put it in the freezer at say 70 degrees, it will freeze much faster than
if you just took it from the faucet at the same 70 degrees.
-- Silvio Levylaura@utcsstat.UUCP (08/17/83)
Another advantage to putting hot water on an ice rink: the ice is rather hacked up, and covered with 'snow' (fine pieces of ice) after a lot of skating has been done. If you use hot water, you can melt the snow and stuff it all into the cracks and holes in the ice. if you roll your rink, you can also squish out the imperfections, but hot water is a lot easier. laura creighton utzoo!utcsstat!laura
turner@randvax.ARPA (08/19/83)
Now wait a minute. Hot water evaporates, losing heat of evaporation and cooling the remaining water. Fine, I'll buy that. But sooner or later the hot water reaches the temperature of the cold water. This takes some amount of time. Now, why does the previously hot water freeze faster from this point on? Hot | | <<---------------------fast cooling do to heat of | evaporation | cool cool | | | | <<------------same rate for both pans. | | | | frozen frozen Scott Turner
bam@sdchema.UUCP (Bret Marquis) (08/21/83)
The point behind boiling cold water rather than hot is that it hasn`t been through your water heater and been stored in your pipes. I've always considered that a bunch of hot air and tend to use hot water for the obvious reason that it takes less heat to boil it. Colorado river water tastes terrible anyway and I doubt if I'd notice the difference. Bret Marquis
dee@cca.UUCP (Donald Eastlake) (08/23/83)
Another case of self fulfiling prophesy: If using hot water for
freezing causes more frost and if using hot water to freeze when you
have frost works better because it melts through the frost and makes
better contact, then people who think it works better to use hot water
will find this to be true.
+ Donald E. Eastlake, III
ARPA: dee@CCA-UNIX usenet: {decvax,linus}!cca!dee