I shoulda put an X thru that x.

That was known as “Trial by Water” and, I suppose, must be considered nearly infallible.

It also figured, sardonically, in piece by Mark Twain called (if I recall now after over 60 years) “The Eskimo Maiden’s Romance” and concerned determining the purloiner of a single fish-hook; it all ended happily: the innocent beaux did, indeed, drown and the fish-hook was later found in his love’s (the Eskimo maiden) hair.

However, it doesn’t float as a result of its drying out enlarging the air sac. If that happened, no change in overall weight or density would have occurred. The decrease in density that could cause it to float is the result of outside air having penetrated the shell and membrane (air which could, presumably, carry bacteria.

It’s still not at all clear whether it’s possible for bacteria (chiefly of interest Salmonella) to occur within an egg with uncompromised shell.

About 15 years ago, there seemed to be evidence that “perfect” eggs could yet be contaminated. A number of states (here in the US) enacted legislation “tightening up” the storage and handling of eggs in restaurants; but, of greatest poublicity and importance, banned the serving of raw egg (as occurs especially in the tableside preparation of Caesar’s Salad dressing). Last I remember, the original information was found to have been faulty. Don’t know how the new regulations were affected. My opinion is that it’s still an poor practice to allow eggs to sit out of refrigeration for any more than a few minutes before preparation/consumption (especially if such consumption is to be raw). Salmonella can certainly occur on the outside and it’s not always possible to detect an egg whose shell has been compromised by small cracks, etc.