Geissler Tubes.
Sealed tubes of glass containing highly rarefied gases, and provided
with platinum electrodes extending through the glass tightly sealed as
they pass through it, and often extending a short distance beyond its
interior surface.
On passing through them the static discharge luminous effects are
produced varying with the degree of exhaustion, the contents (gas), the
glass itself, or solutions surrounding it. The two latter conditions
involve fluorescence phenomena often of a very beautiful description.
The pressure of the gas is less than one-half of a millimeter of
mercury. If a complete vacuum is produced the discharge will not pass.
If too high rarefaction is produced radiant matter phenomena (see
Radiant State) occur.
Geissler tubes have been used for lighting purposes as in mines, or for
illuminating the interior cavities of the body in surgical or medical
operations.
Generating Plate.
The positive plate in a voltaic couple, or the plate which is dissolved;
generally a plate of zinc.
Synonyms--Positive Plate--Positive Element.
Generator, Current.
Any apparatus for maintaining an electric current. It may be as regards
the form of energy it converts into electrical energy, mechanical, as a
magneto or dynamo electric machine or generator; thermal, as a
thermo-electric battery; or chemical, as a voltaic battery; all of which
may be consulted.
Generator, Secondary.
A secondary or storage battery. (See Battery, Secondary.)
German Silver.
An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to
its high resistance and moderate cost and small variation in resistance
with change of temperature, it is much used for resistances. From Dr.
Mathiessen's experiment the following constants are deduced in legal
ohms:
Relative Resistance (Silver = 1), 13.92
Specific Resistance at 0° C. (32F.), 20.93 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 2.622 ohms.
1 foot long, 1/1000 inch thick, 125.91 "
1 meter long, weighing 1 gram, 1.830 "
1 meter long, 1 millimeter thick, 0.2666 "
Resistance of a 1 inch cube at 0°C. (32° F.), 8.240 microhms.
Approximate percentage increase of resistance per 1° C. (1.8° F.) at
about 20° C. (68° F.), 0.044 per cent.
Gilding, Electro-.
The deposition of gold by an electric current, or electrolytically in
the electroplating bath.
Gilding Metal.
A special kind of brass, with a high percentage of copper, used to make
objects which are to be gilded by electrolysis.