A simple polarographic drop-time controller

A commercial electronic timer element (Signetics Timer 555) is useful in constructing polarographic drop-time controller. The present apparatus consists of an astable pulse generator, time delay pulse generator, and monostable pulse generator with an auxiliary pulse generator which activates a solenoid to knock off the mercury drop. Each pulse generator is constructed by using the same timer element with an appropriate R-C network. The circuit diagram with complete description of parts is given (Fig. 2). The apparatus incorporates a relay which cuts off the polarographic current signal to recorder at the moment of drop dislodging in order to suppress the noise accompanying the drop fall (Fig. 3c). This device is particularly helpful in ac polarography(Fig. 4). When applied to dc polarography it realizes "tast polarography" quite simply, since the large charging current at the beginning of the growth of drop is eliminated. The construction is very easy and the stability is excellent (±5 ms for four months).