How the Retort Works

The retort simplifies the alembic's two-piece design into one sealed vessel. The bulb at the wide end holds the material to be heated, whether a liquid to be distilled or a solid to be decomposed by heat, and the neck is drawn out long and thin, then bent downward at an angle so its open tip points at or into a receiving vessel set below and to the side. Heat applied to the bulb drives off vapor, which travels up and along the neck; because the neck is unheated and often quite long, the vapor cools as it travels and begins to condense well before it reaches the tip, so droplets run down the inside of the glass and drip out into the receiver under their own weight, with no separate condensing head needed. This makes the retort well suited to dry distillation, heating a solid directly rather than a liquid, since there is no still-head joint to clog or corrode when the material being decomposed gives off caustic or particulate fumes.

The bend in the neck also matters for safety and yield: it keeps the receiver clear of the direct heat of the furnace and lets the operator angle the tip precisely over the mouth of the collecting vessel. A retort cannot easily be taken apart to clean or inspect mid-process, which is the tradeoff for its simplicity, and that limitation is exactly what later multi-piece laboratory glassware was built to solve.