Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site Glacier.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!genrad!decvax!decwrl!Glacier!reid From: reid@Glacier.ARPA (Brian Reid) Newsgroups: net.cooks Subject: Re: Why boil cold water Message-ID: <7285@Glacier.ARPA> Date: Fri, 10-May-85 04:00:20 EDT Article-I.D.: Glacier.7285 Posted: Fri May 10 04:00:20 1985 Date-Received: Sun, 12-May-85 01:23:52 EDT References: <707@dedalus.UUCP> Organization: Stanford University, Computer Systems Lab Lines: 43 > There is actually a scientific reason to boil cold water as opposed to > hot (it may not be the pertinent reason, though). Cold water will boil > FASTER (yep, that's right) than hot water. This is because the cold water > contains more oxygen than the hot water (now what that does is beyond me). > The above strange fact was passed on to the freshman chemistry class I took > in college. I remain deeply skeptical. So much so, in fact, that I went in to my kitchen just now and did an actual experiment. (details of experiment at end of message for those who care). ---------------------------------------------------------------------------- Initial Time to Kilojoules joules/ <-- you can think of temp boil absorbed second this number as the Hot water 60F 204sec 184 901 "boiling efficiency" Cold water 135F 365sec 347 950 ---------------------------------------------------------------------------- The summary result is that hot water boils faster than cold water, as one might have expected. A joule/second is a watt, so what this means is that my 1200-watt burner was delivering 901 watts to the hot water and 950 watts to the cold water. The probable explanation for this is that the energy transfer rate levels off sharply as the water approaches boiling, because of evaporative loss, and that the cold water stays in the high-efficiency range for a larger percentage of the total time. Another way of looking at these numbers is that not only does hot water not boil faster than cold water, it actually takes LONGER, degree for degree, than cold water (by about half a percent). The experiment: cold water boil: run cold tap water for 2 minutes into pan; empty pan and quickly measure in one liter of cold tap water. Let stand for 60 seconds (to equalize temperature of water and pan), then measure temperature and place on preheated electric stove burner. Hot water boil: the same, but use hot tap water. Alternate cold, hot, cold, etc. three times, for a total of six measurements, allowing the burner to reheat for 1 minute in between measurements. The pan was a copper saucepan (lined with nickel) that weighs 616 grams. The specific heat of copper is 0.0949, which means that the pan's heat absorbtion was 5.8% of the water's (mass of nickel assumed to be negligible; specific heat of Nickel is 0.1035) -- Brian Reid decwrl!glacier!reid Stanford reid@SU-Glacier.ARPA