When the glassware was made by hand, the bulb at the bottom varied in size, so each flask had to be filled with the correct volume before the line could be etched on the glass. A tube was used for the neck since the volume filling the tube would change at a consistent rate. ... The flask looks like a pear shaped container.
The bulb at the bottom differed in size when the glassware was produced by hand, so each flask had to be filled with the correct volume before the line could be engraved onto the glass. Since the volume filling the tube will shift at a constant rate, a tube was used for the neck that is tubular to signify when you have the right amount. The flask looks like a bottle shaped like a pear.
