Quick and dirty brine is 1 cup kosher salt to 1 gallon of water. I'll normally throw in a cup of brown sugar and some other goodies to add some more flavor. If you're doing quarters, I wouldn't leave it in the brine for more than a few hours. If I'm feeling adventurous, I'll use Alton Brown's turkey brine, or PatioDaddio's turkey brine, or a buttermilk brine recipe I found somewhere that's awesome. It gives a nice tang to the chicken.
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