────┴──────────┴────────────┴────────────╨─────────────┴────────────┴──────── Footnote 6: In United States—long tons of 2,240 pounds. The well-known “Thomas Slag” which is in demand as a fertilizer on account of its phosphorus content is the by-product of the basic-lined converter. An idea of what the invention of the Bessemer process meant to railroad development alone may be gained by studying for a moment Table No. 1. Wrought iron was our first material for rails, but, being very soft, it did not give long service. But a short time was required for Bessemer steel to displace it for rails when steel became available. The greater uniformity, strength and hardness of the alloy gave such excellent wearing properties that few rails of iron were laid after the year 1880. During recent years rails have been made of greater and greater strength and hardness to keep pace with the fast increasing weight, speed and frequency of railroad trains, steel being susceptible to much modification of properties. Now it appears that Bessemer steel is giving way to other products which show even superior properties. What happened in the railroad world to a great extent has happened elsewhere, as the figures of Table No. 2 show. They are a barometer which indicates what has been our industrial development and our advance in civilization. CHAPTER IX THE OPEN-HEARTH PROCESS Bessemer’s was a wonderful process, but the time seemed to be ripe for great development along metallurgical lines, and the method of converting pig iron into steel which he devised soon had a competitor which was destined eventually to take the lead in steel production. Many years passed before the tonnage turned out annually by Bessemer’s process was equaled by that of the new, but as shown in the last chapter the Siemens-Martin or open-hearth process in 1907 produced the greater tonnage. It has since retained its lead and probably will continue to do so. As far back as 1845 John Marshall Heath took out a patent for a process for making steel patterned after the old puddling process. In a way he may therefore be said to have devised or forecast the open-hearth process, but because of the great obstacles that had to be surmounted in getting a furnace that would fulfill the requirements he was unable to carry out his scheme. You will remember that in the puddling furnace the purified metal became pasty because of its high melting point. Because of the great heat required it was not until the invention of the regenerative system by C. W. Siemens in 1860 that the open-hearth process was possible. Siemen’s furnace was the first one that could keep the iron molten. It was in Birmingham, England, that the first successful open-hearth furnace was used. [Illustration: