Boiled Crabs

Fill a large pot with water about a third of the way.   Put the liquid crab boil, the content of the box of crab boil, onions, lemons, potatoes, salt, and cayenne pepper.  Covered, bring to a hard boil over high heat.   This should take about 10 to 15 minutes.  Add the blue crabs, cover and bring to a boil once again.  When the steam starts to escape from the lid, let cook for another 10 to 15 minutes.  Now turn off the heat and let the crabs soak for 10 more minutes.  They should now be ready to eat.