The way I heard about this topic was that one should always use the hot water tap when filling ice cube trays so that the cubes would freeze faster and would be clearer. Never was it suggested that the water actually be hot. The logic behind this is that the hot water tank and pipes contain less minerals from being used less than the cold water pipes and this makes the difference. I live in Phoenix which has very alkaline and mineral rich water and this bit of wisdom seems to be true. I suppose distilled water could be tested against cold tap water for speed of freezing, but the clarity issue does seem to be a reality at least in these here parts of the desert. Somebody out there should try it just writing this was enough work for me.
looppr
Phoenix, AZ
When you start a thread, looppr, it’s helpful to other readers if you provide a link to the column. Saves searching time, and helps keep us on the same page. In this case, I assume it’s Which freezes faster, hot water or cold water? - The Straight Dope
No biggie, you’ll know for next time.
Never heard that one about the hot and cold pipes, looppr, but it’s interesting. I wonder if there’s anything to it.
I’ve never been in a big enough hurry for ice to worry about it, but for the record I never bought into the “hot water freezes faster” thing. But, I always used hot water, because there’d always be little bits of ice from the previous cubes stuck to the trays. Hot water would melt those bits away so the next cube wouldn’t be fragmented.
I don’t know about minerals and all that, but hot water definitely has less dissolved air, which would make a difference in clarity. As to the original question, Wikipedia, s.vv. “Mpemba Effect”, has an introduction to the subject.
If hot water freezes faster than cold water:
Place an ice cube tray with cold water and another with hot water in the freezer. If the hot freezes faster, that seems too me to mean that at some point before freezing they would be of the same temperature.
The only way the question is sensible is if two water samples at equal weight were frozen in the same conditions, and the composition of the water was identical. In that case, the colder water freezes faster. Clearly 1 gram of 100 degree water will freeze faster than 1 kilogram of 99 degree water, and pure water will freeze faster than an equal weight of salt water. In all of the cases I’ve ever seen cited to show that hotter water freezes faster, evaporation reduces the amount of hot water, or as in the OP differing levels of dissolved substances change the characteristics of the water. The water has to come from the same source, and the containers have to be covered.
There was another thread about this topic where it was mentioned that in non-frost free freezers, the kind that you had to thaw out every once in awhile, the hot metal ice cube tray would melt through the frost and ice to come in contact with the metal surface of the freezer. That would make that particular ice cube tray less insulated from the refrigerant and therefore would freeze faster than the cold water tray, well insulated from the refrigerant.
The Mpemba effect is actually quite interesting. According to Wikipedia, the effect was known to classical scientists (and apparently even to ancient people in general) and thus the behavior must occur over a significant range of temperatures and conditions. There are a few different things that appear to have influence on the apparently anomalous result, and none of them can individually account for the phenomenon. Water is a truly baffling substance in many ways; this is only one of them.
You actually shouldn’t use hot water from your tap for consumption. Hot water sits in your hot water heater until it is ready to use. Since it is hot, it can dissolve more crud from your hot water heater and pipes. This is especially true if you live in an older home that used lead solder in the water pipes.
The “instant” hot water faucets are different. The water is cool and heated as it is needed.
Which was my point in the old thread. At that instant, they are equal. You cannot say that one is cooling faster than the other from then on.
However, it became obvious that we weren’t talking about water in our water, but water with other things dissolved in it; chemicals and/or gases, such as might be in hot water from some sources. Then the equation changes, and two trays at the same temp might not perform the same if one has more than water.
So you pay to heat the water, then you pay again to cool it down. Unless there is some other advantage, seems kinda like a double waste of energy, doesn’t it?
A-ha! This “someone” must work for the power company.