Gas mantle

The mantle is a roughly pear-shaped fabric bag, made from silk, ramie-based artificial silk, or rayon. The fibers are impregnated with rare-earth metallic salts; when the mantle is first heated in a flame, the fibers burn away in seconds and the metallic salts convert to solid oxides, forming a brittle ceramic shell in the shape of the original fabric. A mantle glows brightly in the visible spectrum while emitting little infrared radiation. The rare-earth oxides (cerium) and actinide (thorium) in the mantle have a low emissivity in the infrared (in comparison with an ideal black body) but have high emissivity in the visible spectrum. There is also some evidence that the emission is enhanced by candoluminescence, the emission of light from the combustion products before they reach thermal equilibrium.[2] The combination of these properties yields a mantle that, when heated by a kerosene or liquified petroleum gas flame, emits intense radiation that is mostly visible light, with relatively little energy in the unwanted infrared, increasing the luminous efficiency.

The mantle aids the combustion process by keeping the flame small and contained inside itself at higher fuel flow rates than in a simple lamp. This concentration of combustion inside the mantle improves the transfer of heat from the flame to the mantle. The mantle shrinks after all the fabric material has burned away and becomes very fragile after its first use.

• 
  Gas mantle in a street lamp (cold)
• 
  Hot gas mantles. The lowest visible mantle has partially broken, reducing its light output.
• 
  An 85 mm Chance Brothers Incandescent Petroleum Vapour Installation

For centuries, artificial light has been generated using open flames. Limelight was invented in the 1820s, but the temperature required to produce visible light through black-body radiation alone was too high to be practical for small lights. In the late 19th century several inventors tried to develop an effective alternative based on heating a material to a lower temperature but using the emission of discrete spectral lines to simulate white light.

Many early attempts used platinum-iridium gauze soaked in metal nitrates, but these were not successful because of the high cost of these materials and their poor reliability. The first effective mantle was the Clamond basket in 1881, named after its inventor. This device was made from a cleverly produced matrix of magnesium oxide, which did not need to be supported by a platinum wire cage, and was exhibited in the Crystal Palace exhibition of 1883.

The modern gas mantle was one of the many inventions of Carl Auer von Welsbach, a chemist who studied rare-earth elements in the 1880s and who had been Robert Bunsen's student. Ignaz Kreidl worked with him on his early experiments to create the Welsbach mantle. His first process used a mixture of 60% magnesium oxide, 20% lanthanum oxide and 20% yttrium oxide, which he called "Actinophor" and patented in 1887, US patent issued on March 15, 1887, # 359,524. These original mantles gave off a green-tinted light and were not very successful. Carl Auer von Welsbach's first company established a factory in Atzgersdorf in 1887, but it failed in 1889. In 1889, Welsbach received his first patent mentioning thorium, March 5, 1889, US patent #399,174. In 1891 he perfected a new mixture of 99% thorium dioxide and 1% cerium dioxide that gave off a much whiter light and produced a stronger mantle. After introducing this new mantle commercially in 1892, it quickly spread throughout Europe. The gas mantle remained an important part of street lighting until the widespread introduction of electric lighting in the early 1900s.[3]

Mantles in their unused flat-packed form

To produce a mantle, cotton is woven or knit into a net bag, impregnated with soluble nitrates of the chosen metals and then heated; the cotton burns away, and the nitrates are converted to nitrites, which fuse together to form a solid mesh. As the heating continues, the nitrites finally decompose into a fragile mesh of solid oxides of very high melting point.

Early mantles were sold in the unheated cotton mesh condition, since the oxide structure was too fragile to transport easily. The mantle was converted to working form when the cotton burned away on first use. Unused mantles could not be stored for very long, since the cotton quickly rotted due to the corrosive nature of the acidic metal nitrates, a problem that was later addressed by soaking the mantle in an ammonia solution to neutralize the excess acid.

Later mantles were made from guncotton (nitrocellulose) or collodion rather than ordinary cotton, since extremely fine threads of this material could be produced, but it had to be converted back to cellulose by immersion in ammonium sulfide before first use, since guncotton is highly flammable and can be explosive. Later, it was discovered that a cotton mantle could be strengthened sufficiently by dipping it in a solution of collodion, which coated it with a thin layer, which would be burned off when the mantle was first used.

Mantles have a binding thread to tie them to the lamp fitting. Until asbestos was banned due to its carcinogenicity, an asbestos thread was used; modern mantles use a wire or a ceramic fiber thread.

• Candoluminescence
• Coleman lantern
• Clamond basket
• Gas lighting

• "Lighting" . Encyclopædia Britannica. 16 (11th ed.). 1911. pp. 651–673.
• A Brief History of the Incandescent Mantle Pressure Lamp
• Auer von Welsbach
• Australian Radiation Protection and Nuclear Safety Agency article "Radioactivity in Lantern Mantles"
• Document at New Jersey Consumer and Environmental Health Services containing a description of contamination at former factory site at Camden, New Jersey.
• Clamond Gas Burner: Scientific American October 2, 1886