The discovery that the flame escaping from the throat of the blast furnace was nothing else than burning carbon led Faber du Faur at Wasseralfugen in 1837 to invent the successful and highly valuable method of utilising the unburnt gas from the blast furnace for heating purposes, and to heat the blast itself, and drive the steam engine that blew the blast into the furnace, without the consumption of additional fuel. This also led to the invention of separate gas producers. Bunsen in 1838 made his first experiments at Hesse in collecting the gases from various parts of the furnace, revealing their composition and showing their adaptability for various purposes. Thus, from a scientific knowledge of the constituents of ores and of furnace gases, calculations could be made in advance as to the materials required to make pig iron, cast iron, and steel of particular qualities. In the process of puddling difficulty had been experienced in handling the bloom or ball after it was formed in the furnace. A sort of squeezing apparatus, or tongs, called the alligator, had been employed. In 1840 Henry Burden of America invented and patented a method and means for treating these balls, whereby the same were taken directly from the furnace and passed between two plain converging metal surfaces, by which the balls were gradually but quickly pressed and squeezed into a cylindrical form, while a large portion of the cinders and other foreign impurities were pressed out. We have described how by Cort’s puddling process tremendous labour was imposed on the workmen in stirring the molten metal by hand with “rabbles.” A number of mechanical puddlers were invented to take the place of these hand means, but the most important invention in this direction was the revolving puddlers of Beadlestone, patented in 1857 in England, and of Heaton, Allen and Yates, in 1867-68. The most successful, however, was that of Danks of the United States in 1868-69. The Danks rotary puddler is a barrel-shaped, refractory lined vessel, having a chamber and fire grate and rotated by steam, into which pig iron formed by the ordinary blast furnaces, and then pulverised, is placed, with the fuel. Molten metal from the furnace is then run in, which together with the fuel is then subjected to a strong blast. Successive charges may be made, and at the proper time the puddler is rotated, slowly at some stages and faster at others, until the operation is completed. A much more thorough and satisfactory result in the production of a pure malleable iron is thus obtained than is possible by hand puddling.