The 4067 is an electrometer pentode for use in pH meters. An electrometer device is as close as possible to an electrostatic device with a very high input impedance and thus almost no input current or loading to the measuring probe.
The 4067 is a true pentode with three wire grids. The red spot indicates the position of pin one.
The five connecting wires. The control grid wires are too fine to be seen.
The 4067 would typically be used as an impedance transformer between the very high impedance sensor and a low impedance micro-ammeter. The cathode follower circuit above is one such circuit.
The thin glass tube envelope is 8 mm in diameter, and excluding the base pins is 34 mm tall.
Reference: Datasheet. Type 4067 was first introduced in 1957.