Electro-dynamometer, Siemens'.
An apparatus for measuring currents by the reaction between two coils,
one fixed and one movable, through which the current to be measured
passes. It is one of the oldest commercial ammeters or current
measurers. It comprises a fixed coil of a number of convolutions and a
movable coil often of only one convolution surrounding the other. The
movable coil is suspended by a filament or thread from a spiral spring.
The spring is the controlling factor. Connection is established through
mercury cups so as to bring the two coils in series. In use the spring
and filament are adjusted by turning a milled head to which they are
connected until the coils are at right angles. Then the current is
turned on and deflects the movable coil. The milled head is turned until
the deflection is overcome. The angle through which the head is turned
is proportional to the square of the current. The movable coil must in
its position at right angles to the fixed one lie at right angles to the
magnetic meridian.
Thus in the diagram, Fig. 143 A B C D is the fixed coil; E F G H is the
movable coil; S is the spiral spring attached at K to the movable coil.
The arrows show the course of the current as it goes through the coils.
Electrolier.
A fixture for supporting electric lamps; the analogue in electric
lighting of the gasolier or gas chandelier. Often both are combined, the
same fixture being piped and carrying gas burners, as well as being
wired and carrying electric lamps.
Electrolysis.
The separation of a chemical compound into its constituent parts or
elements by the action of the electric current. The compound may be
decomposed into its elements, as water into hydrogen and oxygen, or into
constituent radicals, as sodium sulphate into sodium and sulphion, which
by secondary reactions at once give sodium hydrate and sulphuric acid.
The decomposition proceeds subject to the laws of electrolysis. (See
Electrolysis, Laws of.) For decomposition to be produced there is for
each compound a minimum electro-motive force or potential difference
required. The current passes through the electrolyte or substance
undergoing decomposition entirely by Electrolytic Conduction, q. v. in
accordance with Grothüss' Hypothesis, q. v. The electrolyte therefore
must be susceptible of diffusion and must be a fluid.
The general theory holds that under the influence of a potential
difference between electrodes immersed in an electrolyte, the molecules
touching the electrodes are polarized, in the opposite sense for each
electrode. If the potential difference is sufficient the molecules will
give up one of their binary constituents to the electrode, and the other
constituent will decompose the adjoining molecule, and that one being
separated into the same two constituents will decompose its neighbor,
and so on through the mass until the other electrode is reached. This
one separates definitely the second binary constituent from the
molecules touching it.