In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid. The most common objective is to prevent vapors being evacuated from an experiment from entering a vacuum pump where they would condense and contaminate it.

For a vacuum pump that requires oil, collection of solvent vapors is essential to prevent them from collecting in the vacuum pump’s oil. Also, if corrosive or water vapors collect in pump oil, the vacuum pump will be damaged and eventually the vacuum pump will cease beyond repair.

For non-oil based vacuum pumps, collecting the vapors prior to the vacuum pump makes the evaporation system a closed system, preventing vapors from passing through the vacuum pump and into the environment.

How Cold Traps work:

In the evaporation process, the Cold Trap is the coldest spot in the evaporation system. Vapors naturally migrate to the coldest spot, where they freeze and are trapped in the condenser. Because of this natural migration of the vapors, Cold Traps can also increase evaporation rates since vapors are collected as a frozen solid (and are therefore not condensed inside the vacuum tubing, which would slow evaporation). 

the witches Tit hols over 10lbs of dry ice and will contain vapor in a cloud around the bottom of trap. It is totally amazing!