Gas lighting was a formerly common application of ordinary coal-gas, the gas obtained by heating coal, to the lighting of buildings, streets, &c. In 1739 the Reverend Clayton published a paper in
the Philosophical Transactions, on the inflammable nature of the gases obtained by the decomposition of pit-coal in heated close vessels; but no practical application of thia discovery was made before 1792, when a Mr. Murdoch, a native of Ayrshire, in the employ of Messrs. Watt and Boulton, lighted his own house and offices at Redruth on this principle. In 1798 he erected a gas apparatus on a large scale at the SohoFoundry, Birmingham, and in 1802 Le Bon lighted his house in Paris by gas, and made a proposal to supply the whole city. In 1803 Mr. Winsor exhibited gas illuminations at London in the Lyceum, and afterwards raised the sum of 50,000 pounds from a number of subscribers who formed themselves into a National Light and Heat Company in 1810. With this money Mr. Winsor lighted Pall Mall, but was soon succeeded by Mr. Samuel Grieg, who invented the hydraulic main, the wet-lime purifier, and the wet gas-meter. From this time coal gas became the most common illuminating agent wherever it could be prepared economically.
Another kind of gas for lighting that came into use to some extent, namely, water-gas, was produced from the decomposition of water in the form of steam by passing it through incandescent fuel.
Gas was obtained from coal, the best sorts being those bituminous coals known in England by the name of cannel, and in Scotland by the name of parrot. The coal was distilled in retorts of cast-iron or later, after about 1900, more generally of fire-clay, heated to a bright red heat. As they issued from the retort into the hydraulic main the products of distillation contained vapours of tar, together with steam impregnated with more or less ammoniumcarbonate, sulphide, hydrosulphide, thiosulphite, etc. These vapours would condense in the pipes in which the gas must be distributed, and would clog them up; they therefore had to be so far removed by previous cooling as to cause no inconvenient condensation at ordinary temperatures. The crude gas contained besides, sulphuretted hydrogen, the combustion of which would cause an offensive smell. Carbonic acid weakened the illuminating power of the gas, and also had to be removed.
The profitable consumption of gas, whereby the strongest light can be had at the least expenditure of gas, depends considerably upon the form of the burner, and the mode by which the flame is fed with the air necessary for its combustion. There must be a sufficient supply of oxygen to convert the carbon of the gas into carbonic acid, and the hydrogen into water. If there is not a sufficient supply of oxygen, the flame will be smoky from excess of carbon. In this case the remedy is either to reduce the supply of gas or increase the supply of air. This may be effected by modifying the form of the burner, or in the case of the Argand burner by having a different shape of glass chimney. As to the form of the burner, it was found that a plain jet about 6 mm in diameter at the orifice, will not give a flame free from smoke of a greater height than 60 mm but the same quantity of gas which would give a smoky flame from a plain jet, would produce a clear bright flame by extending or dividing the aperture of the jet so as to expose a larger surface of flame to the atmosphere. It was not, however, necessary to increase the superficial area of the flame;
it could even be diminished with a more intensely luminous effect by having instead of one aperture two small ones pierced at an angle to each other, so that the jets crossed each other a system known as the fishtail or union jet.
Another form was the slit or batwing burner, in which a clean slit was cut across the top of the beak. In the Argand burner a circle of small holes supplied the gas, and a current of air was admitted through the centre of the flame, which was surrounded by a glass chimney. In the Welsbach incandescent lamp the light was produced by causing the burning gas to raise to white heat what is known as the mantle, suspended over the burner. The mantle consisted essentially of cottonyarn steeped in a solution of salts of such metals as thorium, cerium, yttrium, lanthanum, magnesium, etc, and when the thread had been burned away there remained a skeleton of the oxides of the metals used. Research Gas Lighting
Abbreviations
Research Actinium
