Hefner Flame Standard

The legal standard of candle-power adopted in 1893 by the Physikalisch-Technische Reichsanstalt of Germany is the lamp devised in 1884 by F. von Hefner-Alteneck. A thin German-silver tube exactly 25mm high, 8mm internal diameter, and 0.15mm thick holds a wick of untwisted cotton; the fuel is amyl acetate. The candle-power of the reddish flame depends appreciably on its height, and somewhat on humidity and barometric pressure. In 1909 and again in 1921, its value was agreed to be exactly nine-tenths of the international candle.