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E is a battery, whose EMF in this work should be obviously
more than EMF of normal or testing element. The normal element is
the battery of electromotive force (Weston’s element).

Weston element consists of a glass H-like vessel; electrodes are
soldered into its lower ends. There is mercury in one of its knees,
cadmium amalgam - in another one. Saturated solution of cadmium

sulphate is served as electrolyte; so that it makes it always possible to
keep the solution saturated, some crystals of this element are put in it.
Mercury is a positive pole, cadmium amalgam is a negative one.
EMF of normal

element at temperature
200C is EMF 1.0183 V.
Weston element is

polarized at
comparatively weak
currents and for short

term work and prolonged
storage. So, it can be
used only for a few times.

One must be careful with
a normal element, don’t turn it over or put on the side. Don’t touch
both poles at the same time, it can lead to a short test, because the
current in the circuit should not be more than 1 mA.

4. Wiring Scheme and Laboratory Bench

Fig 3.1 and Fig. 3.2 only illustrate the principle of determination

of electromotive force by compensation method. Wiring scheme
presents all the sets that are necessary to accomplish laboratory work
(Fig 4.1).

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