Carbon Lamps

Carbon is a wonderful substance. It is familiar to us in the form of soot, lampblack, charcoal, graphite (the "lead" of lead pencils) and diamond. The puzzle which the electric lamp inventor had to solve was to get this protean substance in the form of a fine tough thread. Edison scoured the world of botany to discover a natural fibre which would serve the purpose; and he at last selected bamboo. Swan took the more scientific line of making a carbon filament from the beginning, as it were. His raw material was nothing more recondite than cotton-wool. "From cotton-wool to candle power" was the phrase which once summed up the making of electric lamps.

The first step was to dissolve the cotton-wool in chloride of zinc, producing after treatment which need not be detailed here, a soft mass, with the consistency of golden syrup. This mass was squirted slowly through a small hole into a jar of alcohol, which converted it into a whitish thread, not unlike fine marcaroni, and after washing and drying, the coils, now fine and tough, were wound on "formers" which gave the filaments the looped curv e familiar in the old carbon lamps. When these formers were placed in a furnace and baked, everything except the carbon was driven off, and the original mass of cottonwool was thus transformed into hard and tough threads of pure carbon.

The rest of the process of lamp-making lay in mounting each thread in a glass bulb from which all the air was extracted. Were any air left in the bulb, the carbon filament, raised to a white heat by the electric current, would burn and disappear. Mou nted in a vacuum it would live for several hundred hours of light-giving.


From The Story of the Lamp, on Kilokat's Antique Light Bulb Site<