Hg Franck-Hertz tube

For demonstrating the discontinuous release of energy by free electrons upon collision with mercury atoms, and for determining their excitation energy. The Franck-Hertz curve is plotted either point-by-point with indicating instruments or continuously by means of a recorder or CASSY.
Vacuum tube with indirectly heated cathode, emission control grid, anode grid, collector and a mercury drop which vapourizes when the tube is heated. Please note: the Franck-Hertz tube (555 854) can only be used in conjunction with the corresponding sockets (555 864/555 865). It is not possible to run it on the socket for the old Franck-Hertz tube (555 85, no longer available).