A direct reading hydrogen-ion meter / by C.G. Pope and F.W. Gowlett.

  • Pope, C. G.
Date:
[1927?]
Catalogue details

Licence: In copyright

Credit: A direct reading hydrogen-ion meter / by C.G. Pope and F.W. Gowlett. Source: Wellcome Collection.

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    proportionally to its magnitude. When the grid ((<2) Fig. 3) is made more negative with f-espect to the filament the anode current is decreased. Now the normal anode current of the valve is of the order of twelve hundred micro-amperes, and as the milli-voltmeter gives &. full scale deflection for a current of 240 micro-amperes, some method must be adopted (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) Four electrode thermionic valve. Milli-voltmeter. 12 volt accumulator. Main filament circuit resistance. Reverse current resistance (filament circuit). Grid bias resistance. Vernier rheostat. Main reverse current resistance. Calibrated reverse current resistance used with the hydrogen electrode system. Calibrated reverse current resistance used when standardizing the apparatus. Calibrated reverse current resistance used with the quinhydrone electrode system. Shunt resistance for milli-voltmeter. Spring switch keeping the shunt across the milli-voltmeter until the button is depressed. Main filament circuit switch. Standard Weston cell. Double pole three way switch. Fig. 3. Circuit Diagram The reverse current is obtained in the following way. The resistances (4), (5), (6) and the filament resistance (c) form a potentiometer circuit, the amount of current passing being controlled by the rheostat (7). If the current is kept constant, the potential differences between the ends of resistances (4), (5), (6) and the filament resistance (c) will be constant. It will be seen that two currents can pass through the meter (2) in reverse directions, first, from the valve filament to the valve anode (the electron stream) through the meter to the junction of resistances (4) and (5) and so back through resistance (4) to the filament; second, from the junction of resistance (4) and (5) through the meter, resistance (8) and one of (9), (10) or (11), and thence via resistance (5) to the junction of (4) and (5). The amount of current passing through the meter in the