Will a chicken sit on on eggs that are not fertile?

Yes, chickens will sit on eggs that are not fertile. A chicken will sit on a wooden egg. You need to determine if they are fertile or not. First, do you have a rooster? You need one rooster to every 10 - 12 hens. Second, 10 days after the lay date, you need to candle the eggs. This checks for the precence of a developing embryo. This is done by holding a strong light up to the egg in a dark room, if it is fertile you should be able to see a darkened area, some blood vessels, and maybe some movement. Compare the egg in question with a fresh lain egg and you should be able to see the difference between a fertile egg and a "clear" one. You can use a strong flashlight, a homemade device, or a candling device from a feed and seed store or a hatchery. There are other areas on the coop that talk about candling. Hopefully in 21 days you will have some chicks - good luck and let us know what happens....