Electro-physiology.
The science of the electric phenomena of the animal system. It may also
be extended to include plants. The great discovery of Galvani with the
frog's body fell into this branch of science. The electric fishes,
gymnotus, etc., present intense phenomena in the same.
Electroplating.
The deposition by electrolysis of a coating of metal upon a conducting
surface. The simplest system makes the object to be plated the negative
electrode or plate in a galvanic couple. Thus a spoon or other object
may be connected by a wire to a plate of zinc. A porous cup is placed
inside a battery jar. The spoon is placed in the porous cup and the zinc
outside it. A solution of copper sulphate is placed in the porous cup,
and water with a little sodium or zinc sulphate dissolved in it,
outside. A current starts through the couple, and copper is deposited on
the spoon.
A less primitive way is to use a separate battery as the source of
current; to connect to the positive plate by a wire the object to be
plated, and a plate of copper, silver, nickel or other metal to the
other pole of the battery. On immersing both object and plate (anode) in
a bath of proper solution the object will become plated.
In general the anode is of the same material as the metal to be
deposited, and dissolving keeps up the strength of the bath. There are a
great many points of technicality involved which cannot be given here.
The surface of the immersed object must be conductive. If not a fine
wire network stretched over it will gradually fill up in the bath and
give a matrix. More generally the surface is made conductive by being
brushed over with plumbago. This may be followed by a dusting of iron
dust, followed by immersion in solution ot copper sulphate. This has the
effect of depositing metallic copper over the surface as a starter for
the final coat.
Attention must be paid to the perfect cleanliness of the objects, to the
condition of the bath, purity of anodes and current density.
Voltaic batteries are largely used for the current as well as special
low resistance dynamos. Thermo-electric batteries are also used to some
extent but not generally.
Electro-pneumatic Signals.
Signals, such as railroad signals or semaphores, moved by compressed
air, which is controlled by valves operated by electricity. The House
telegraph, which was worked by air controlled by electricity, might come
under this term, but it is always understood as applied to railroad
signals, or their equivalent.