Galvanometers

W = working electrode SW = slide-wire resistor T = tap key i = galvanometer. 

The electric current is used to drive a recorder of some kind, which can be an oscilloscope, pen recorder, or galvanometer UV recorder. 

A suitable slip-coil, having tipproximtitely 700 turns of I mm diameter insulated wire, is passed axially over the motor and its two etids are connected to t centre-/ert galvanometer. When the motor is running, the gal ttnotiieter pointer will oscillate. The tuimber of oscillations should be cotmted in one direction only, that is to the left or to the right, for t period of, say. 20 seconds. 

Spulen-galvanometer, n. moving-coil galvanometer. -lack, m. (Elec.) insulating varnish (Textiles) bobbin finish, -ol, n. spooling oil. -wicklung, /. (Elec.) coil winding, -wider-stand, m. (Elec.) coil resistance. 

All currents that had to be measured were sent to a central measurement room in which many mirror galvanometers were situated on top of vibration-free columns that were separated from the foundations of the building. One should realize that the many announcements in the early literature of the liquefaction of specific gases pertained to not much more than a mist or a few drops Kamerlingh Onnes planned to make liquid gases by the gallon. A separate hydrogen liquefaction plant was located in a special room with a roof that could be blown off easily. 

The coil (wound on a light metal former) can be suspended by a fine strip of phosphor bronze between the pole pieces. Attached to this suspension is a small mirror which reflects on to a scale a beam of light which is focused upon it. An instrument of this kind is known as a D Arsonval galvanometer and is used in potentiometer circuits and various methods of measurement of resistance. 

The zero-resistance ammeter is seldom employed for routine testing. This instrument requires careful handling to avoid damage, in particular to the galvanometer. Usually two permanent test leads are installed at a set distance apart, and by the initial use of a zero-resistance ammeter a calibration chart of potential between the two leads and current in the structure is drawn up. Thus when routine testing is made, it is only necessary to measure the... 

To avoid the errors of polarisation and stray currents, special resistivity meters are employed. One form of these uses an alternating current produced from batteries by a vibrator. The effective resistance is measured by a modified Wheatstone bridge with balance indicated by a galvanometer. 

If it is desired to use the biamperometric method for detecting the end point, then the calomel electrode and also the silver rod (if used) must be removed and replaced by two platinum plates 1.25 cm x 1.25 cm. The potentiometer (or pH meter) used to measure the e.m.f. must also be removed, and one of the indicator electrodes is then joined to a sensitive galvanometer fitted with a variable shunt. The indicator circuit is completed through a potential divider... 

Procedure. Pipette 25.0 mL of the thiosulphate solution into the titration cell e.g. a 150mL Pyrex beaker. Insert two similar platinum wire or foil electrodes into the cell and connect to the apparatus of Fig. 16.17. Apply 0.10 volt across the electrodes. Adjust the range of the micro-ammeter to obtain full-scale deflection for a current of 10-25 milliamperes. Stir the solution with a magnetic stirrer. Add the iodine solution from a 5 mL semimicro burette slowly in the usual manner and read the current (galvanometer deflection) after each addition of the titrant. When the current begins to increase, stop the addition then add the titrant by small increments of 0.05 or 0.10 mL. Plot the titration graph, evaluate the end point, and calculate the concentration of the thiosulphate solution. It will be found that the current is fairly constant until the end point is approached and increases rapidly beyond. 

Fill a test-tube with the sample to be determined to a depth similar to that used for the standards, and insert into the instrument. Note the galvanometer deflection evaluate the concentration from the calibration curve. 

The procedure is as follows. In switch position 1 and while repeatedly depressing tap key K, the variable resistor R, is adjusted once for each measurement to zero current through galvanometer G, so that the emf of the standard cell C8t (Weston 1.01832 V) becomes accurately compensated over the constant resistor Rj. Next, in switch position 2 the unknown emf of cell Cx is... 

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