Reference line on distilling flask?

Question

What is it for? Is it important?

Answer 1

There have been two different lines scribed on common distillation flasks. One on the stem and one on the bowl of the flask. Some flasks have no line; some have only one.

A line on the stem is usually the lowest point to place the thermometer bulb. The bottom of the bulb should not be below the line. The entire bulb should be between the line and the side arm.

A line on the bowl (bottom part of the flask) usually marks the upper limit of liquid placed into the flask for distillation. This is to avoid possible "bumping" of non-distilled liquid and contaminating the distillate.