when heating a beaker, where should the burner flame be located for maximum heating?

3 answers

middle of the beaker I assume.
Under the middle of the beaker.
Under the beaker with the tip of the inner blue cone of the burner just touching. However, I never like to heat a beaker directly (unless it's made of Vycor). I prefer to place the beaker on top of a wire gauze and heat the wire gauze. Beakers made of Pyrex have been known to crack if heated directly.