The finger
The Friedrichs condenser (sometimes incorrectly spelled Friedrich's) was invented by Fritz Walter Paul Friedrichs, who published a design for this type of condenser in 1912. It consists of a large water-cooled finger tightly fitted inside a wide cylindrical housing. The finger has a helical ridge along its length, so as to leave a narrow helical path for the vapor. This arrangement forces the vapor to spend a long time in contact with the finger.