Who Invented the Twisty Little Bit of Wire Inside the
Light Bulb?
We all learned in our history
classes that Thomas Edison invented the light bulb in 1879 and that the first
successful filament was a carbonized piece of cotton thread that burned for
13.5 hours. Today, light bulb filaments are not something we think about,
unless they burn out, but their early development is a fascinating story of 19th
century chemistry and materials science.
Edison decided to develop an
incandescent lighting system at a time when he was acknowledged as the nationıs
foremost inventor of telegraphic equipment. By the fall of 1877 Edison had developed some critical
insights and announced to the press that he would soon have a commercially
successful system.
He concluded that a current
regulator was needed prevent the bulbıs filament from overheating. Either a thermal expansion device or
telegraph style relay could be used to open the circuit when the current was
too high. Circuit breakers
protecting each filament meant that light bulbs would need to be wired in
parallel.
Fortunately Edison knew
enough about Jouleıs and Ohmıs laws to recognize that high-resistance lamps
would work most efficiently in parallel circuits. Experiments carried out in the Menlo Park, New Jersey,
laboratories, revealed that a filamentıs energy consumption was proportional to
its radiating surface, not its resistance. In other words, high resistance lamps would not require more
energy than low resistance ones.
Decreasing the radiating surface actually produced more light. Thus the ideal filament would be a
long, thin wire with high resistance.
And once he reached this point in October of 1878, Edison believed that
the incandescent light was as good as already invented.
By the time Edison had
started his lighting project in 1877, some twenty inventors had already built
light bulbs with either platinum or iridium filaments heated in air, or carbon
filaments heated in a vacuum.
Platinum was the ideal material.
It had a high melting point, could be wound in a tight coil, and
resisted oxidation. Carbon on the
other hand was too easily oxidized and difficult to protect with the current
vacuum technologies. Earlier
inventors tried unsuccessfully to get around this problem by using carbon
filaments in nitrogen and even hydrocarbon atmospheres.
To overcome platinumıs
expense Edison tried to find new sources and develop platinum alloys. Both efforts failed, as did attempts to
use less expensive metals. By this
time the press, which had come to expect miracles from Edison, (a view which
Edison himself strongly encouraged) was becoming impatient for results.
It is well beyond the scope of
this article to describe Edisonıs 1878 work on electrical generators,
generating publicity, and how financial backing was arranged for the
incandescent lighting system.
Suffice to say that these efforts were critical for bringing the project
to completion.
It was while working with
metallic filaments that Edison and his staff made one of their most important
contributions to chemistry.
Microscopic and chemical examinations of platinum/iridium alloy filaments
that had been heated in air revealed that oxidation was a major problem. The metal seemed to adsorb gasses
during heating and that its melting point depended on the amount of gas in its
pores. What was obviously needed
was a better vacuum pump.
By combing the scientific
literature the Menlo Park staff learned that the two best pumps were the
Sprengel and Geissler mercury types.
Unable to acquire them, Edison commissioned a glass blowing firm to
build new pumps that combined the best features of both. A McLeod gauge was added and the
laboratory soon had the worldıs most efficient (though sometimes temperamental)
vacuum pump.
Heating platinum in a better
vacuum degassed the filaments and in turn enabled them to be thinner and to
withstand higher temperatures.
It would also make the system cheaper since individual circuit breakers
were no longer needed for each lamp.
Edison eventually presented
his work on gasses in metals to the American Association for the Advancement of
Science. It is recognized as a
major contribution to the chemistry of metals. All of this work however did not solve the problem of
platinumıs cost.
Armed with a better vacuum
pump, Edison now turned to carbon as a potential filament. He sought a naturally occurring fiber
that could be carbonized. Among
the many fibers tried were human hairs, animal hairs, thinly sliced horn, all
kinds of threads, and botanical specimens from around the world. In order to improve their strength,
Edison tried impregnating the carbonized fibers with rock candy, whale oil,
cotton oil, and any number of hydrocarbons. Ultimately, the most successful fiber proved to be thinly
sliced strips of bamboo.
Meanwhile, the press, public,
and financial backers were growing impatient. Edison needed light bulbs for his demonstration projects.
And so the first bulbs had carbonized paper filaments. Even the finest paper had an irregular
distribution of fibers and varied in thickness. Paper filaments only lasted about 300 hours.
It is at this point that the
research split into two very different paths. Inspired by the nineteenth century ideal of a bounteous
natural world that was filled with good things for all mankind, Edison sought a
natural fiber somewhere in ³Godıs almighty workshop.² His rivals attempted to create a synthetic one.
As they saw it, only an
amorphous, dense, and completely uniform carbon filament would provide long
lasting illumination. No natural
fiber could ever meet these requirements.
Edisonıs two principle rivals
were William Sawyer of New York and Edward Weston of Newark, New Jersey. Weston was a native of England who came
to the United States as a young man of twenty in 1870. He settled in New York where his first
position was with a manufacturer of photographic chemicals. The chance to revamp an almost-bankrupt
plating company led Weston into the field of electrochemistry. Since at that time there was no
reliable source of electric current, Weston began building his own dynamos,
which in turn became his primary business.
He moved to Newark, New
Jersey in 1875 and by 1877 had acquired a former synagogue on Washington Street
for use as the nation's first electrical machinery plant. Armed with good dynamos and a very
thorough knowledge of chemistry, Weston took up the challenge of electric
lighting a year before Edison.
Many readers of the Indicator will recognize Weston as the inventor of the Normal
Cell (the fist standard unit of a volt) and founder of the Weston Instrument
Company, one of the worldıs foremost electrical instrumentation
manufacturers. Both of these
achievements were in the future.
Although his first
commercial successes would be with outdoor arc lights, Weston also worked to
develop an incandescent light for indoor use. His first light bulb filaments were made by squeezing a
mixture of carbon dust and tar through a narrow aperture. But when these fibers proved
non-homogeneous, Weston thought back to his days as a photographic chemist and
resolved to try celluloid.
Celluloid is made by
combining nitrated cellulose with camphor under high heat and pressure. Because it is highly flammable, a
stable form was required for use as a filament. Weston reasoned that since the starting material had been oxidized,
treatment with a reducing agent would de-nitrify and convert the celluloid back
into cellulose. In September of
1882, he patented a process where celluloid was immersed in baths containing
hydrated ammonium sulphide, ferrous chloride, or ferrous sulphate. According to the inventor, the
resulting material was non-flammable, dense, flexible, and tough.
Filaments were cut from
sheets of this material, which Weston named ³Tamidine². The filaments were heated to remove the
dissolved gasses, carbonized, and finally had the ends plated in copper.
Unlike Weston who was a
trained scientist, and Edison who was a highly disciplined researcher, William
Sawyer was a journalist and part time inventor of telegraph equipment. Despite limited financing, poor theoretical
understanding, and a drinking problem, Sawyer did manage to produce a working
light bulb with a carbon filament.
But he and his backers rushed their bulbs into production without first
taking the time to refine their product or their production techniques. They were forced to quit the project by
June of 1878.
Sawyer did create one
process that was vital to the production of carbon filaments, he made them
³self repair.² Gently heating the
filaments in a hydrocarbon atmosphere caused the weak spots and surface
pockmarks to heat up and glow brightly.
Carbon was deposited on these spots until the entire filament had a
uniform cross section. Weston made the same discovery at about the same time
but Sawyer was first to patent the process.
Meanwhile, back at Menlo
Park, Edison had not been idle. Once bamboo was found to be an effective
filament, another search was made for the optimal species. First, specimens of all tropical grass
species that could be obtained in the United States were tried. Agents were then sent to Cuba and South
America to hunt for tropical grasses.
William H. Moore was sent to Japan and China to obtain more exotic
varieties of bamboo. After an
exhaustive search, a contract was signed with a Japanese grower near
Kyoto. Before the end of the
filament search, some 6000 species of bamboo had been tried.
Trained scientists shook
their heads over Edisonıs bamboo search and his detractors have pointed to the
effort as a monumental waste of time.
They missed an important point, even if the search failed to generate a
single usable filament, it did generate huge amounts of publicity. Edison made a point of being on the
pier whenever one of his filament hunters returned home, then with the press
watching, he loudly questioned the man about his results. Edison was also an avid reader of Jules
Verneıs novels and the worldwide search through mountains and jungles was like
living out one of Verneıs plots.
And the Japanese filaments
did work well. By 1880, Edison was
producing bulbs that could last up to 1500 hours.
Even as the last of
Edisonıs filament hunters were returning to New Jersey, the industrialist Hiram
Maxim (later famous for his machine guns) was manufacturing bulbs with Tamidine
filaments. Patent royalties from
these filaments proved immensely valuable to Weston. Lasting up to 2000 hours, Tamidine quickly became a
serious competitive challenge for bamboo and other plant fibers. Until the
introduction of tungsten filaments, many of the worldıs light bulbs were made
with this material.
In 1906, General Electric
introduced incandescent bulbs with tungsten filaments.
Of the twenty or so
inventors who had worked on incandescent lights before Edison, most are
remembered only in the better history books. Edward Weston may have had the better filament but lacked
Edisonıs impressive financial backing and favorable press. Although he was awarded the contracts
for lighting Newarkıs streets and later the Brooklyn Bridge, Weston eventually
dropped out of the lighting business and turned his attention to electrical
measuring instruments. The Weston
Instrument Company was founded in 1888.
Their factory at the corner of Newarkıs Plane and Orange Streets turned
out thousands of instruments.
Westonıs patent portfolio included advances in electroplating,
electrical meters, fuses, batteries, and motors. The growing fame of Westonıs Newark research laboratory is
said to have goaded Edison into abandoning Menlo Park and constructing the huge
research facilities in West Orange, New Jersey.
In recent years, the story
of the light bulb has attracted scholarly attention and even a Smithsonian
Exhibition. For readers interested
in learning more, I recommend Edison's Electric Light: Biography of an
Invention by Robert Douglas Friedel
and Edison, A Life of Invention by
Paul Israel.