History

For centuries, artificial light had been generated using open flames. Limelight had been invented in the 1820s but the temperature required 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 spectral lines to simulate white light.

Many early attempts used platinum / iridium gauzes soaked in the metal nitrates, but were not successful because of the high cost of the materials and poor reliability. The first effective mantle was the Clamond basket in 1881, named after its inventor. It was exhibited in the Crystal Palace exhibition of 1883. This device was made from a mixture of magnesium hydrate, magnesium acetate and water which was squeezed through holes in a plate to form threads, which were then moulded into a basket shape and ignited. The acetate burnt, the combustion products forming a matrix to support the magnesium oxide formed as the hydrate decomposed. The fragile structure was supported by a platinum wire cage and heated by a coal gas flame.

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 a student of Robert Bunsen. His first process used a mixture of 60 percent magnesium oxide, 20 percent lanthanum oxide and 20 percent yttrium oxide, which he called Actinophor, and patented in 1885.

The original mantles gave off a green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889. In 1890 he discovered that thorium was superior to magnesium, and in 1891 perfected a new mixture of 99 percent thorium dioxide and 1 percent cerium dioxide gave off a much "whiter" light, and the thorium oxide added considerably to the strength of the mantle. After introducing it 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.

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

Early mantles were sold in the unheated cotton mesh condition, since the oxide structure was too fragile to transport easily and the purchaser carried out the conversion when it was first used. The cotton quickly rotted because of the corrosive nature of the acidic metal nitrates (although was later reduced by soaking the mantle in ammonia solution to neutralise the excess acid).

Later mantles were made from guncotton or collodian rather than ordinary cotton, since extremely fine threads of it could be produced; it was converted back to cellulose before heating (since these materials are highly flammable or explosive) by dipping in ammonium sulfide.

It was discovered that the finished mantle could be strengthened sufficiently by dipping in a solution of collodion which would coat it with a thin layer of the material to be burnt off when the mantle was first used, although modern mantles are now usually sold in their original fabric condition.

Early mantles often had a binding thread of asbestos for tying onto the lamp fitting, but because of its carcinogenic properties it has been replaced with wire in modern mantles.

 

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(Mahatma Gandhi 1869-1948)