How can I incubate eggs that will hatch female chicks only?
A study in Australia (Australian Journal of Agricultural Research 11(4) 664 - 672) has shown that eggs stored at 40 degrees Fahrenheit (rather than the recommended 60 degrees) hatch out more females than males. That is surprising! However storing your eggs at colder temperatures before hatching doesn't actually change the ratio of male to female eggs. It has been shown that the male embryos are preferentially killed off by colder storage temperatures, while the female embryos handle the chilling better.
In other words, your overall hatch rate suffers if the eggs are stored at cool temperatures, but those that DO hatch are slightly more likely to be females. Unfortunately, there is no way to know which eggs will hatch males and which females, as you can read in the "related questions" below.