ANUFACTURER OF INCANDESCENT
FILAMENT LAMPS

Thousands of lamps are burned out for the sake of making improvements. The
electrical energy used is equivalent to that consumed by a city of 30,000
inhabitants]

Edison in 1878 attacked the problem of producing light from a wire or
filament heated electrically. He used platinum wire in his first
experiments, but its volatility and low melting-point (3200 deg.F.) limited
the success of the lamps. Carbon with its extremely high melting-point
had long attracted attention and in 1879 Edison produced a carbon
filament by carbonizing a strip of paper. He sealed this in a vessel of
glass from which the air was exhausted and the electric current was led
to the filament through platinum wires sealed in the glass. Platinum was
used because its expansion and contraction is about the same as glass.
Incidentally, many improvements were made in incandescent lamps and
thirty years passed before a material was found to replace the platinum
leading-in wires. The cost of platinum steadily increased and finally in
the present century a substitute was made by the use of two metals whose
combined expansion was the same as that of platinum or glass. In 1879
and 1880 Edison had succeeded in overcoming the many difficulties
sufficiently to give to the world a practicable incandescent filament
lamp. About this time Swan and Stearn in England had also produced a
successful lamp.

In Edison's early experiments with filaments he used platinum wire
coated with carbon but without much success. He also made thin rods of a
mixture of finely divided metals such as platinum and iridium mixed with
such oxides as magnesia, zirconia, and lime. He even coiled platinum
wire around a piece of one of these oxides, with the aim of obtaining
light from the wire and from the heated oxide. However, these
experiments served little purpose besides indicating that the filament
was best if it consisted solely of carbon and that it should be
contained in an evacuated vessel.

One of the chief difficulties was to make the carbon filaments. Some of
the pioneers, such as Sawyer and Mann, attempted to cut these from a
piece of carbon. However, Edison and also Swan turned their attention to
forming them by carbonizing a fiber of organic matter. Filaments cut
from paper and threads of cotton and silk were carbonized for this
purpose. Edison scoured the earth for better materials. He tried a
fibrous grass from South America an