INVENTION OF THE TUNGSTEN LAMP
Alexander Just and Franz Hanaman in 1902 were laboratory assistants to the Professor of Chemistry in the Technical High School in Vienna. Just was spending his spare time in another laboratory in Vienna, attempting to develop a boron incandescent lamp. In August of that year he engaged Hanaman to aid him in his work. They conceived the idea of making a lamp with a filament of tungsten and for two years worked on both lamps. The boron lamp turned out to be a failure. Their means were limited; Hanaman’s total income was $44 per month and Just’s was slightly more than this. In 1903 they took out a German patent on a tungsten filament, but the process they described was a failure because it produced a filament containing both carbon and tungsten. The carbon readily evaporated and quickly blackened the bulb when they attempted to operate the filament at an efficiency higher than that possible with the ordinary carbon filament. Finally in the latter part of the next year (1904) they were able to get rid of the carbon and produced a pure tungsten filament.
Tungsten had been known to chemists for many years by its compounds, its oxides and its alloys with steel, but the properties of the pure metal were practically unknown. It is an extremely hard and brittle metal and it was impossible at that time to draw it into a wire. Just and Hanaman’s process of making a pure tungsten filament consisted of taking tungsten oxide in the form of an extremely fine powder, reducing this to pure tungsten powder by heating it while hydrogen gas passed over it. The gas combined with the oxygen of the oxide, forming water vapor which was carried off, leaving the tungsten behind.
The tungsten powder was mixed with an organic binding material, and the paste was forced by very high pressure through a hole drilled in a diamond. This diamond die was necessary because tungsten, being so hard a substance, would quickly wear away any other kind of die. The thread formed was cut into proper lengths, bent the shape of a hair pin and the ends fastened to clamps. Current was passed through the hair pin in the presence of hydrogen gas and water vapor. The current heated the hair pin, carbonized the organic binding material in it, the carbon then combining with the moist hydrogen gas, leaving the tungsten particles behind. These particles were sintered together by the heat, forming the tungsten filament. Patents were applied for in various countries, the one in the United States on July 6, 1905.
The two laboratory assistants in 1905 finally succeeded in getting their invention taken up by a Hungarian lamp manufacturer. By the end of the year lamps were made that were a striking success for they could be operated at an efficiency of 8 lumens per watt. They were put on the American market in 1907, the first lamp put out being the 100-watt size for 110-volt circuits. This was done by mounting several hair pin loops in series to get the requisite resistance, tungsten having a low specific resistance. The issue of the American patent was delayed owing to an interference between four different parties, each claiming to be the inventor. After prolonged hearings, one application having been found to be fraudulent, the patent was finally granted to Just and Hanaman on February 27, 1912.
Tungsten Lamp, 1907.
The original 100 watt tungsten lamp was nearly three times as efficient as the carbon lamp, but its “pressed” filament was very fragile. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.
This “pressed” tungsten filament was quite fragile, but on account of its relatively high efficiency compared with other incandescent lamps, it immediately became popular. Soon after its introduction it became possible to make finer filaments so that lamps for 60, 40 and then 25 watts for 110-volt circuits were made available. Sizes up to 500 watts were also made which soon began to displace the enclosed carbon arc lamp. Lamps were also made for series circuits in sizes from 32 to 400 candlepower. These promptly displaced the carbon and Gem series lamps. The high efficiency of the tungsten filament was a great stimulus to flashlights which are now sold by the millions each year. The lighting of railroad cars, Pullmans and coaches, with tungsten lamps obtaining their current from storage batteries, soon superseded the gas light formerly used. In some cases, a dynamo, run by a belt from the car axle, kept these batteries charged.
Drawn Tungsten Wire Lamp, 1911.
Scientists had declared it impossible to change tungsten from a brittle to ductile metal. This, however, was accomplished by Dr. Coolidge, and drawn tungsten wire made the lamp very sturdy. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.