Wikipedia claims 10°C, but it also says “Sulfuric acid in solution with water causes significant freezing-point depression of water’s melting point”, which suggests that both Harry and HowStuffWorks are right. Harry is probably thinking of the pure acid.
(Also, that wouldn’t affect his plan. He only needs it solid so he can transfigure it, and the only significance of the freezing point is that it’s easily reachable, not exactly how high it is above 0°C.)
So it does; that must be Harry’s source (^_^). It would be consistent that 98% freezes at 3° and 100% freezes at 10°, but HSW also says that you can’t get more than 98% (presumably because it draws water from the air, it doesn’t say).
I agree, this doesn’t really affect anything. If Harry can’t make a concentration that freezes at 10° but can make one that freezes at 3°, then that’s what he’ll use. (I only looked into this because it was such a surprising claim.)
That does not appear to be correct. If http://science.howstuffworks.com/sulfuric-acid-info.htm is accurate, then frozen sulfuric acid ice cannot get much warmer than frozen water and the more usual concentrations freeze at much lower temperatures. However, high concentrations (98%, freezing at 3°C), while more expensive, are easily available online http://www.sciencecompany.com/Sulfuric-Acid-Concentrated-1L-P6550.aspx (plus it doesn’t seem hard to concentrate yourself http://chemistry.about.com/od/makechemicalsyourself/a/How-To-Make-Sulfuric-Acid-At-Home.htm), so Harry could probably get a supply that would still work; he’d just have to keep it in ice, rather than merely keep it refrigerated.
Wikipedia claims 10°C, but it also says “Sulfuric acid in solution with water causes significant freezing-point depression of water’s melting point”, which suggests that both Harry and HowStuffWorks are right. Harry is probably thinking of the pure acid.
(Also, that wouldn’t affect his plan. He only needs it solid so he can transfigure it, and the only significance of the freezing point is that it’s easily reachable, not exactly how high it is above 0°C.)
So it does; that must be Harry’s source (^_^). It would be consistent that 98% freezes at 3° and 100% freezes at 10°, but HSW also says that you can’t get more than 98% (presumably because it draws water from the air, it doesn’t say).
I agree, this doesn’t really affect anything. If Harry can’t make a concentration that freezes at 10° but can make one that freezes at 3°, then that’s what he’ll use. (I only looked into this because it was such a surprising claim.)
And, he can easily get to 4 degrees on fairly large masses using the cooling spell he used on Hermionie’s corpse.
Cooling spell, right, no need for ice!