Mercury

I was looking for something in the archives of my towns newspaper amd i came across the an article stating that mercury treated bread was used to find a drowned body in the river. it was an experiment , one that worked apprently because the bread stopped floating where the body was found , which is what was hypothesised. is this possible?and what does the mercury have to do with this? mind you this experiment was condcuted in 1931

It is also told in "tom sawyer" by mark twain. this is an old folk belief, more honored in the belief than the practice...