rated
Voltameter, or Measure of Voltaic electricity.

But before he can apply this measure he must clear his ground of
numerous possible sources of error. The decomposition of his acidulated
water is certainly a direct result of the current; but as the varied and
important researches of MM. Becquerel, De la Rive, and others had shown,
there are also secondary actions which may materially interfere with and
complicate the pure action of the current. These actions may occur in
two ways: either the liberated ion may seize upon the electrode against
which it is set free, forming a chemical compound with that electrode;
or it may seize upon the substance of the electrolyte itself, and thus
introduce into the circuit chemical actions over and above those due to
the current. Faraday subjected these secondary actions to an exhaustive
examination. Instructed by his experiments, and rendered competent by
them to distinguish between primary and secondary results, he proceeds
to establish the doctrine of 'Definite Electro-chemical Decomposition.'

Into the same circuit he introduced his voltameter, which consisted of
a graduated tube filled with acidulated water and provided with platinum
plates for the decomposition of the water, and also a cell containing
chloride of tin. Experiments already referred to had taught him that
this substance, though an insulator when solid, is a conductor when
fused, the passage of the current being always accompanied by the
decomposition of the chloride. He wished to ascertain what relation this
decomposition bore to that of the water in his voltameter.

Completing his circuit, he permitted the current to continue until 'a
reasonable quantity of gas' was collected in the voltameter. The circuit
was then broken, and the quantity of tin liberated compared with the
quantity of gas. The weight of the former was 3.2 grains, that of the
latter 0.49742 of a grain. Oxygen, as you know, unites with hydrogen in
the proportion of 8 to 1, to form water. Calling the equivalent, or as
it is sometimes called, the atomic weight of hydrogen 1, that of oxygen
is 8; that of water is consequently 8 + 1 or 9. Now if the quantity of
water decomposed in Faraday's experiment be represented by the number 9,
or in other words by the equivalent of water, then the quantity of tin
liberated from the fused chloride is found by an easy calculation to be
57.9, which is almost exactly the chemical equivalent of tin. Thus both
the