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.)
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 97. The previous thread is at nearly 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system.
Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: