All About Engines

Fuel and Its Problems 335 gradually, the mixture becomes more and more nearly in the correct proportion for an explosion. The flame grows smaller, a sharply defined inner blue cone makes its appearance, and, finally, the flame “ strikes back,” producing an ordinary luminous gas flame starting from the small orifice through which the gas enters. Before this occurs the velocity of the gases passing out of the burner has always been at least as great as the rate at which the flame tends to pass down the tube. When it does occur, when the flame “ strikes back,” the velocity of combustion exceeds the velocity with which mixture flows up- ward. An explosion has not occurred, but the rate of combustion has been greatly increased. Now, Professor W. A. Bone found that if he closed the end of a tube with a disc of porous material some- thing like fireclay, passed an explosive mixture of gases into the open end, and applied a light at the other, combustion went on in the pores of the disc, causing it to glow brightly. This was a case of sur- face action. The gases will not pass through the disc rapidly enough in either direction to allow of a flame on the outside, or an explosion inside, but combus- tion proceeds rapidly just within the surface of the material itself. As a result of this discovery we have the Bone- court Boiler, and Figure 182 on Plate 32 illustrates one of several forms the apparatus takes. The boiler is fitted with tubes, 6 inches in diameter, and each tube is packed with blocks of special material upon the surface of which the mixed gases burn. The