Remember how you can tell if
an egg is too old to eat with a float test? You can use a similar test on day 23 or 24 with eggs that haven’t hatched to make sure the chicks inside are really dead.
The first step is to wait until most of your eggs have hatched. I like to wait 24 hours after the last chick comes out of the shell, then take a close look at the remaining eggs to make sure none of them has pipped or been cracked. (You don’t want to do a float test on a pipped egg or the chick will drown.) This test is mildly traumatic to a chick inside an unpipped egg, so there’s no reason to risk it until you’re getting ready to toss the unhatched eggs.
Now fill a container with water that’s roughly baby bottle temperature — warm enough that you
can barely feel it when touched to the underside of your wrist. (This is the same temperature water you use when proofing yeast for bread, about 100 degrees Fahrenheit.) Wait until the water has stopped moving in the container, then take an egg out of the incubator and carefully lower it into the water with a spoon.
If your egg sinks to the bottom, it was probably infertile from the beginning and is definitely
a dud now. If it floats, take a careful look at the floating pattern.
Does the big end stick up above the water with the narrow end pointing straight down? Your egg is probably a “yolker” that either was a dud from the beginning or died young.
On the other hand, if your egg floats at more of an angle, almost horizontally, the chick might be alive inside. (The chick is definitely still alive if the egg starts to move around on its own.) Carefully take the egg out of the water, wipe it dry, and pop it back in the incubator for another day or two.
In the past, I’ve been guilty of pulling late hatchers out of the incubator prematurely, but with this float test in my arsenal, I suspect my hatch rate will continue to rise.