Electro-capillarity.
The relations between surface tension, the potential difference and the
electrostatic capacity of fluids in contact. Although nominally in
contact such surfaces are separated by about one-twenty-millionth of a
centimeter (1/50000000 inch) ; thus a globule of mercury and water in
which it is immersed constitute an electrostatic accumulator of definite
electrostatic capacity. Again the mercury and water being in electric
connection differ in potential by contact (see Contact Theory). A
definite surface tension is also established. Any change in one of these
factors changes the other also. A current passed through the contact
surfaces will change the surface tension and hence the shape of the
mercury globule. Shaking the globule will change its shape and capacity
and produce a current. Heating will do the same. (See Electrometer,
Capillary; and Telephone, Capillary.) Mercury and water are named as
liquids in which the phenomena are most conveniently observed. They are
observable in other parallel cases.
Electro-chemical Equivalent.
The quantity of an element or compound liberated from or brought into
combination, electrolytically, by one coulomb of electricity. The
electro-chemical equivalent of hydrogen is found by experiment to be
.0000105 gram. That of any other substance is found by multiplying this
weight by its chemical equivalent referred to hydrogen, which is its
atomic or molecular weight divided by its valency. Thus the atomic
weight of oxygen is 16, its valency is 2, its equivalent is 16/2 = 8;
its electro-chemical equivalent is equal to .0000105 X 8 = .000840 gram.
Electro-chemical Series.
An arrangement of the elements in the order of their relative electrical
affinities so that each element is electro-negative to all the elements
following it, and electro-positive to the elements preceding it. The
usual series begins with oxygen as the most electro-negative and ends
with potassium as the most electro-positive element. There is, of
course, no reason why other series of compound radicals, such as
sulphion (SO4), etc., should not also be constructed. For each liquid
acting on substances a separate series of the substances acted on may be
constructed. Thus for dilute sulphuric acid the series beginning with
the negatively charged or most attacked one is zinc, amalgamated or
pure, cadmium, iron, tin, lead, aluminum, nickel, antimony, bismuth,
copper, silver, platinum. In other liquids the series is altogether
different.
Electro--chemistry.
The branch of electricity or of chemistry treating of the relations
between electric and chemical force in different compounds and
reactions. (See Electrolysis--Electrochemical series--Electro-chemical
Equivalent .)