The vacuum adapter is used during distillations. Vapor enters a condenser, cools and condenses, then drips into the vacuum adapter. If a distillation is carried out at atmosheric pressure, then a test tube can be placed under the adapter. Distilling liquid is collected in the test tube. If a distillation at reduced pressure is necessary, a round bottom flask is placed on the adapter and a hose that leads to a source of vacuum (such as a water aspirator or vacuum pump) is connected at the side arm.