 The additional necks can also allow a dropping funnel to be attached to let reactants slowly drip in.Special electrically powered heating mantles are available in various sizes into which the bottoms of round-bottom flasks can fit so that the contents of a flask can be heated for distillation, chemical reactions, boiling, etc.Heating can also be accomplished by submerging the bottom of the flask into a heat bath, water bath, or sand bath.