Worm

A worm takes the single biggest weakness of a plain alembic head, that it only condenses vapor as fast as the surrounding air can carry heat away, and fixes it by forcing the vapor to travel through cold water instead of cold air. The tube itself does the condensing, not the water directly: vapor enters one end of a metal pipe that has been coiled into a tight spiral, and that coil sits fully submerged inside a barrel, trough, or jacketed vessel kept filled with cold, often continuously replaced, water. As the vapor winds through the coil it loses heat through the metal wall into the surrounding water far faster than a static air-cooled dome ever could, so by the time the vapor reaches the far end of the worm it has almost entirely condensed back into liquid, which drips or runs out of the tube's open end into a waiting receiver.

Coiling the tube rather than running it straight was the key improvement: it let a distiller fit several feet of cooling surface into a compact tub of water instead of needing several feet of open bench space, and it kept the vapor in contact with the cold water for far longer per unit of apparatus size. Because the metal coil could be made from copper, which conducts heat efficiently and does not react with most organic vapors, the worm became the standard condenser wherever a distillery needed to process large volumes quickly rather than a few drops at a time.

Early printed distillation manuals, including Hieronymus Brunschwig's Liber de arte distillandi of 1500, describe delivery pipes, called worms for their crooked or coiled shape, carrying vapor from a still to a receiver set on a stool or small table below. Coiling the pipe and submerging it in cold water was the refinement that turned a simple delivery tube into a true high-efficiency condenser, and the practice was well established in European distilling workshops by the sixteenth century, spreading through the same printed manual tradition that popularized named still heads like the moor's head and the rosenhut. The worm proved so effective that it outlasted almost every other piece of alchemical still equipment: it is the direct ancestor of what a modern chemistry laboratory calls a serpentine condenser or, in one common design, a Graham condenser, and the coil-in-cold-water principle is unchanged in either.

Outside the laboratory, the same apparatus, still called a worm by name, remains the standard condenser in traditional pot-still distilleries making whisky and other spirits, and it gives its name informally to illegal moonshine stills, where "worm" and "still" are used almost interchangeably. Few pieces of alchemical laboratory equipment moved this directly, and under this little a change of name, into both a modern industry and a modern laboratory bench.