[488] Water-gas is a mixture of equal volumes of carbon monoxide and hydrogen, obtained by blowing steam through a glowing coke furnace. At intervals the steam is shut off, and air is blown through to raise the temperature of the coke. In the year previous to that in which Faraday first carburised water-gas, Berzelius had observed that thoria and zirconia, when heated in a non-luminous flame, emit an intense white light. Similar behaviour had long before been observed in the cases of magnesia, alumina, lime, zinc oxide, etc. The first practical application of this property of the oxides was that of Drummond, who in 1826 heated a pencil of lime in the oxy-hydrogen flame and obtained the intense white light which has since become so familiar as the Drummond or ‘lime-light.’ A further development in this direction was due to du Motay and Maréchal, who in 1867 illuminated the Place de Tuileries and the Hôtel de Ville in Paris by means of pencils of compressed zirconia--magnesia was also used--heated by means of oil vapour and oxygen. The use of non-luminous flames to secure illumination, by raising the temperature of solids suspended in them to the point of incandescence was proposed in 1839 by Cruickshank, who used a mantle of platinum wire, covered with lime and rare earths, which he heated by means of water-gas. In 1846 Gillard employed mantles of platinum wire, raised to incandescence in the flame of burning hydrogen, which he obtained by passing steam over heated iron wire; later he used water-gas (1848), his lamps with this modification being employed in Paris and in Philadelphia. Narbonne was later illuminated (1856-1865) by a similar device, but permanent success could hardly be obtained in view of the cost of the platinum mantles, which lasted only a few months. The same mantle was proposed in 1882 by Lewis, the ordinary Bunsen flame being suggested as the source of heat. In the same year Popp exhibited at the Crystal Palace lamps in which a platinum mantle was raised to incandescence by means of a flame of coal-gas and heated air. These attempts, however, served only to show that no permanent advance could be made in this direction.