The floating bread techinique could work if a corpse is floating down a river, and gets stuck in an eddy, then over time sinks there. It would stand to reason that a loaf of bread that is weighted down by mercury could also get stuck in the same eddy. Or if the current were to cause the corpse to get lodged on a pile of stick on a bridge abutment - the loaf would also get lodged there. It isn’t the most accurate way to find something: but it is a way to start. I would use stick rather than a wasting food or dumping a heavy metal into the environment.
I don’t have a copy of the book, and I read it long ago, but it is mentioned in the original question that Huck eats the bread with the mercury in it. Is this true?
I never thought about mercury poisoning, I just used to wonder what kind of bread would still be edible after floating in a river for any length of time. Seems to me it would get soggy pretty quickly.
Sounds like one of Isaac Asimov’s early novels: “Lucky Starr and the Floating Bread Loaves of Mercury.”
“A big double loaf come along, and I most got it with a
long stick, but my foot slipped and she floated out further. Of course I was where the current set in the closest to the shore–I knowed enough for that. But by and by along comes another one, and this time I won. I took out the plug and shook out the little dab of quicksilver, and set my teeth in. It was “baker’s Bread”–what the quality eat; none of your low-down corn-pone.”
by the way, you can get a copy of the book from Project Guttemberg http://tinyurl.com/af3w