It's basic stuff that when something, anything, is heated, it expands, somewhat.
That when whatever something is cooled, it contracts, somewhat.
There is only one exception to this rule that Truly Yours knows of, and that's water at four degrees Centigrade. At that thermal state, whether water is heated or cooled, it expands slightly.
Specifically, one expects an at least slight expansion with the addition of heat (to water - or quite anything else); whereas, water, and (to the best of my knowledge, water only and uniquely) expands slightly when heat is subtracted from it at the cited temperature; then it does what everything else does, that is, then, after it slightly expands, with the subtraction of heat, then, it contracts.
Repeat: Water is the only element known (to the best of this record's knowledge) that behaves this way. If this be the case, we have a unique behavior to consider here, which is an enigma for which - as far as I know - there is no explanation. Since it contradicts the way everything else behaves under the described circumstances, may it be said that there's a flag up on this physical behavior - were we to understand the reason for it, we might understand a lot of other previously unknown, partially understood or altogether misunderstood things...
That's as much as I can share with the Reader at this time on this subject, because it's all I know of it (to the best of my knowledge, what I have described is true, and uniquely true of water at the cusp of freezing. We know that water at freezing temperature may be liquid or solid, even disregarding any salt content, which then maintains a liquid state in water below freezing. No. It may be liquid or solid at freezing temperature of 32oF and 4oC without any salt content).
If I have made myself understandable and am not mistaken about the premise here, might someone either correct me (with a reminder that ice expands from a liquid state), or, perhaps explain why it is that the only thing (known) that expands (slightly) when heat is subtracted from it, before it goes on to contract like all other things subjected to decreased heat.
If everything as I have described it is true, then there's something to be learned here regarding this singular contradiction about expansion and contraction of entities subjected to various temperatures, following the rule of expansion when heated and contraction when cooled. With water at 32oF and 4oC being the only (known) exception.
As I recall and if not mistaken, I first learned this from Guy Murchie in Music of the Spheres (Although, clearly, I alone take the responsibility if I happen to have this bass ackwards?).
Commentary, correction, criticism or contribution requested here. Thank you.
"If I could learn where it all begins and ends, I'd put everything else in the middle." - R.W. Emerson