I am trying to incubate chicken eggs. It is 18 days and 2 have cracked open. The crack is like they are just ?

A common incubation time is 21 days for chickens to hatch, but there is some variation. Are you sure that they're rotten? It could be that they're hatching.

Chicken eggs need humidity, specific temperature and daily turning for the first 19 – 20 days to hatch. No turning the last day or two. If all these are not met each item missing causes a different problem and any surviving chicks are unlikely. A cracking egg is most likely rotten and bacteria are expanding within.

a bad smell is a sure sign of a rotten egg ,does not however mean that all the eggs are bad,when a chick is about to hatch it will break open a tiny hole to start with, the process is called piping ,a series of such close holes all round the periphery of the egg,results in a lid like bit of shell breaking open through which the chicken just drops out.A crack is not the sign of an impending hatch.

The chick has a protuberance at the tip of it's beak called an egg tooth

it soon withers away after the chick has hatched as it has no further fuction to perform.

You most likely have a bad egg or 2 in there. Smell the cracked ones up close. If they smell bad, carefully get rid of them! Check all the others for smell, seeping goo or other signs of a bad egg. Try to candle them if you can. Get rid of any bad ones you find...If they explode in the incubator, you could lose the entire batch because of bacteria.

A good site for info is homesteadingtoday.com

it is unquestionably gross...yet I did certainly have chickens at one ingredient. After pulling my hair out and stepping in one too many piles of (YUCK!!) i desperate it replaced into the two them or me, so off to the community processing farm they went....And upon very final prep for making some fowl soup, sure!! I did certainly discover tiny eggs interior!!!