ilver, and drawn down till the outside diameter
is 1/10 millimeter. The silver coating is then dissolved in a bath of
nitric acid, and the platinum wire is left behind. This wire is then
cut into lengths, bent into a U form, and placed in a glass globe, in
which circulates a current of bicarbonated hydrogen obtained by the
action of sulphuric acid on alcohol. This gas, previously purified,
circulates around the platinum filament, through which an electric
current is passed sufficient to bring it to a red heat. This
decomposes the gas, and a thin coating of absolutely pure carbon is
deposited on the wire. The operation is continued until a sufficient
thickness of carbon has been deposited for each type of lamp, and the
method of regulating the amount of deposit is effected very
simply, and, in fact, almost automatically. Indeed, one of the most
interesting features of the process is its great simplicity, although
it is somewhat more costly than the ordinary methods of producing
incandescence lamps. After having been subjected to the action of
the gas for two or three hours, the filament is taken from the glass
globe, its diameter is carefully measured, the length is calibrated,
and it is set on a platinum support, to which it is soldered by a very
ingenious process. The filament is then introduced into a second
glass globe charged with bicarbonate of hydrogen; it is placed between
pincers that hold the carbon near its union with the platinum, and the
platinum some millimeters below. These pincers are then thrown into
circuit, and a powerful current is passed through the part which is
to be soldered. The platinum and carbon become incandescent, the
bicarbonate is decomposed, and a fresh deposit of carbon solders the
filament to its support. The system thus mounted is placed within the
permanent globe, and a vacuum is obtained in the ordinary way, while
the testing and finishing details present nothing of special interest.
The finished lamp is then photometrically tested, and placed on a
support something like the Edison mounting. Upon it are engraved
the working constants. As an ordinary practical result, these lamps,
working with 50 volts and 1.15 amperes, give a luminous intensity of
20 candles, or the equivalent in luminous spherical intensity of 1.1
Edison A lamps. This result is interesting, especially as the life
of the lamp ranges from 900 to 1,100 hours, as was demonstrated by
various careful tests made with some 2