Originally Posted by Apriljc
Both of my chicken eggs (overdue a bit) floated with just a bit of the egg out of the water. But...shouldn't they float a little anyways, since they have an airspace? Even if they are dead? Because, even if dead, they still have the air space that will make them float....
Huh? What do I made of that? I did not, however, see any wiggling. I candled the eggs also. They look just as they did early this morning.
Yeah, the float test is based on how much air is in the egg. Basically, if the egg sinks then it was most likely an early quitter, as the air cell stops growing when the chick stops developing. But it could also mean that the embryo is/was fully developed but your humidity was WAY too high and the egg didn't lose enough moisture. If your egg floats very high, like with half of the shell above water, then it's no good either, as there's far too much air cell.
If it floats just a little bit like you are describing then it is possibly okay, but not definitely. Like you say, if it developed fine all the way to day 20 or 21 then died, the air cell will be the right size to let it float just a bit, so the floating on its own isn't enough. If your egg is overdue (perhaps due to slightly low temps) but still alive and getting ready to hatch then you should see definite ripples in the water and maybe even the egg bouncing and rocking. Eggs won't wriggle till they're actually just about ready to hatch, so if you float a live egg on, say, day 19 or 20, you probably won't see any movement even though the chick is alive. It only works on chicks that are squirming around ready to pop.
When you say overdue a bit, what day are you on?