How to ensure that eggs get hard boiled on a gas stove? I used to determine the state of eggs by their shell i.e. if the shell is cracked, the eggs have been boiled. But sometimes I have found that even though the shell is cracked, the egg whites are somewhat runny!

Is there a special way of boiling eggs on "gas stove"? Is it necessary to cover them while boiling?

EDIT 1:
Today I punctured the egg top with a pin, but still the egg cracked on boiling :(

EDIT 2:
Today I added a spoon vinegar in the water, and the eggs did NOT crack at all. :)
Just watch the clock, it's the most (if not only) reliable way. And make sure the water stays at or just under boil of course. There's no difference between cooking them on gas or electric, it's just a different way of heating the water :) Depending on how firm you want them, 5-7 minutes should usually be enough in boiling water.