FLAME ARC
Most of the light being emitted by the flame
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°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.
ON THE TESTING-RACKS OF THE MANUFACTURER 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
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 and various kinds of bamboo from other parts of the world. Thin filaments of split bamboo eventually proved the best material up to that time. He made many lamps containing filaments of this material, and even until 1910 bamboo was used to some extent in certain lamps.
Of these early days, Edison said: