Until the invention of the electric lamp, the illumination of living and working space was very much the result of sunlight or of combustion. Since the development of firemaking skills in prehistoric times, the combustion of plant matter, fossil fuels, or animal fat was the only source of lighting available to those who wanted to illuminate the dark spaces in their lives.
From ancient times people had to rely on flames to throw heat and an agreeable yellowish light over reasonable distances. A good deal of technology evolved here and there to optimally capture the heat of combustion to do useful work (stoves, furnaces, and boilers) from readily available fuels.
Lighting technology also evolved to maximally produce illumination from flame. High energy density fuels that offered a measure of convenience for lamp users evolved as well. Liquid fuels like vegetable oils, various nut oils, whale oil and kerosene could flow to the site of combustion and were in some measure controllable for variable output. The simple wick is just such a “conveyance and metering device” for the control of a lamp flame. Liquid fuels flow along the length of a wick by capillary action to a combustion zone whose size was variable by simple manipulation of the exposed wick surface area.
The first reported claim of the destructive distillation of coal was in 1726 by Dr Stephen Hales in England. Hales records that a substantial quantity of “air” was obtained from the distillation of Newcastle coal. It is possible that condensable components were generated, but Hales did not make arrangements to collect them. Sixty years earlier an account of a coal mine fire from flammable coal gases (firedamp) highlighted the dangerous association of coal with volatiles. So, flammable “air’ was associated with coal for some time.
By 1826 a few chemists and engineers were examining the use of combustable gases for illumination. The historical record reveals two types of flammable gas that were derived from coal- coal gas and water-gas. Both gases came from the heating of coal, but under different conditions. Coal gas was the result of high temperature treatment of coal in reducing conditions. It is a form of destructive distillation where available volatiles are released. Depending on the temperature, there was the possibility of pyrolytic cracking of heavies to lights as well.
Water-gas was the result of the contact of steam with red hot coal or coke. The water dissociates into H2 and CO. Water gas is a mixture of hydrogen and carbon monoxide, both of which are combustable. The formation of water-gas is reported to have been discovered by Felice Fontana in 1780.
One of the properties of burning coal gas or water-gas was the notably meager output of light from the flame. Workers like Michael Faraday and others noted that these new coal derived gases provided feeble illumination, but if other carbonaceous materials could be entrained, then a brighter flame could result. It was during the course of investigations on illumination with carburized water-gas that Faraday discovered bicarburet of hydrogen, or benzene.
About this time, an engineer named Donovan also noted that if other carbonaceous materials were to be entrained into water-gas, then the light output was enhanced. So, in 1830, engineer Donovan installed a “carburetted” water-gas lighting system for a short run in Dublin.
Coal gas was first exploited for lighting by the Scottish engineer William Murdoch. Murdoch began his experiments in 1792 while working for Watt and Boulton in England. By the late 1790’s, Murdoch was commercially producing coal gas lighting systems. His home was the first to be lit with coal gas.
The carburization of water gas eventually became an established industry in America in the second half of the 19th century. The treatment of gases, especially with the discovery of natural gas in Ohio, increased the commercial viability of lighting with gas. Carburization of water gas was aided by the discovery of hydrocarbon cracking to afford light components that could be used for this purpose.
Here is where the subject of this post comes in. Since thorium is frequently associated with rare earth elements (REE) the connection of REE’s to the issue of illumination begins in the laboratories of Berzelius in about 1825. Berzelius had observed that when thoria and zirconia were heated in non-luminous flames, the metal oxides glowed intensely. But this was not a new phenomenon. Substances like lime, magnesia, alumina, and zinc oxide were known to produce a similar effect. Goldsworthy Gurney had developed the mechanism of the Limelight a few years before. In the limelight, a hydrogen-oxygen flame played on a piece of lime (calcium oxide) to produce a brilliant white glow. This effect was soon developed by Drummond to produce a working lamp for surveying.
The work of Berzelius was an important step in the development of enhanced flame illumination. He had extended the range of known incandescent oxides to include those that would eventually form the basis of the incandescent mantle industry. Thoria (mp 3300 C) and zirconia (mp 2715 C) are refractory metal oxides that retain mechanical integrity at very high temperature. This is a key attribute for commercial feasibility.
Numerous forms of incandescent illumination enhancements were tried in the middle 19th century. Platinum wire had the property of glowing intensely in non-luminous flames. But platinum was not robust enough for extended use and was quite rare and consequently very expensive. By 1885, a PhD chemist named Carl Auer von Welsbach patented an incandescent mantle which was to take the gas light industry to a new level of performance. Welsbach studied under professor Robert Bunsen at the University of Heidelberg.
Welsbach fashioned the incandescent mantle into the form that is familiar to anyone today who has used a Coleman lantern. The original mantle was comprised of a small cellulose nitrate bag that had been impregnated with magnesium oxide, lanthanum oxide, and yttrium oxide in the ratio of 60:20:20. The mantle gave off a greenish light and was not very popular.
By 1890, Welsbach produced an improved incandescent mantle containing thoria and ceria in a ratio of 99:1. This mantle emitted a much whiter light and was very successful. Many combinations of zirconia, thoria, and REE metal oxides were tried owing to their refractory nature, but the combination of thoria-ceria at the ratio of 99:1 was enduring.
Welsbach made another contribution to the commercialization of REEs. Welsbach had experimented with mischmetal and was interested in its pyrophoric nature. He had determined that a mixture of mischmetal and iron, called ferrocerium, when struck or pulled across a rough surface, afforded sparks. In 1903 Welsbach patented what we now call the flint. In 1907 he founded Treibacher Chemische Werke GesmbH. Today Treibacher is one of the leading REE suppliers in the world.
REE’s in Greenland.