In the Gerard incandescent lamp the carbons have the form of a V. They
are obtained by agglomerating very finely powdered carbon, and passing it
through a draw plate. At their extremity they are cemented together with
a small quantity of carbon paste, and their connection with the platinum
conducting wires is effected by means of a cylinder of the same paste
surmounted by a cone. These couplings secure a good contact, and, by
their dimensions, prevent the attachments from becoming hot and
consequently injuring the carbon at this point. The cone forms a
connection of decreasing section, and prevents the carbon from getting
broken during carriage.
This process of manufacture permits of obtaining lamps of all
intensities, from 3 candles up. The following, according to Mr. Gerard,
are the consumptions of energy in each size of lamp:
Candles. Volts. Amperes.
No. 0. 10 16 1.5
" 1. 25 25 2
" 2. 50 30 2.5
[Illustration: GERARD'S INCANDESCENT LAMP.]
It will be seen that these lamps require a relatively intense current
with much less fall of potential than the Swan, for example--this being
due to the diameter of the filament. But, what is an inconvenience as
regards mounting, if we wish to supply them by ordinary machines (for
they must be mounted in series of 3 on each derived circuit if the
machine gives, as most frequently the case, 100 volts), is an advantage
as regards the quality and steadiness of the light and the duration of
the lamps.
The part in which the energy is expended is homogeneous, as might be
supposed from the mode of manufacture, and as may be ascertained from a
microscopical examination, and it is exempt from those variations in
composition that are found in carbons of a vegetable nature, like the
Edison. Besides, being of relatively large diameter, the lamp is capable
of supporting a very great increase of temperature.
The process employed for fixing the lamps is as simple as can be. Each
platinum wire is soldered to a piece of copper that surrounds the base of
the lamp and that is fixed to the glass with a special cement. These two
armatures intertwine, but at a sufficient distance apart to prevent
contact. They carry a longitudinal projection and an inflation that fit
by hard friction into two copper springs connected electrically with the
circuit. It is only necessary to lift the lamp in order to remove it from
the support; and the contrary operation is just as easy.--_Le Genie
Civil_.
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