A recent improvement in the handling of iron from the blast furnace is shown in Fig. 255. Heretofore, the iron was run in open sand moulds on the floor and allowed to cool in bars called “pigs,” which were united in a series to a main body of the flow, called a “sow.” To break the “pigs” from the “sow,” and handle the iron in transportation, was a very laborious and expensive work. The illustration shows two series of parallel trough moulds, each forming an endless belt, running on wheels. The molten cast iron is poured direct into these moulds, and as they travel along they pass beneath a body of water, which cools and solidifies the iron into pigs, and then carries them up an incline and dumps them directly into the cars. [Illustration: FIG. 255.--CASTING AND LOADING PIG IRON.] _Open Hearth Steel_ is not so cheap as Bessemer steel, but it is of a finer and more uniform quality. Bessemer steel is made in a few minutes by the most energetic, rapid and critical of processes, while the open hearth steel requires several hours, and its development being thus prolonged it may be watched and regulated to a greater nicety of result. For railroad rails and architectural construction Bessemer steel still finds a great field of usefulness, but for the finest quality of steel, such as is employed in making steam boilers, tools, armor plate for war vessels, etc., steel made by the open hearth process is preferred. It consists in the decarburization of cast iron by fusion with wrought iron, iron sponge, steel scrap, or iron oxide, in the hearth of a reverberatory furnace heated with gases, the flame of which assists the reaction, and the subsequent recarburization or deoxidation of the bath by the addition, at the close of the process, of spiegeleisen or ferro-manganese. The period of fusion lasts from four to eight hours. The advantages over the Bessemer process are, a less expensive plant and the greater duration of the operation, permitting, by means of sampling, more complete control of the quality of the product and greater uniformity of result. The British patents of Siemens, No. 2,861, of 1856; No. 167, of 1861, and No. 972, of 1863, for regenerative furnaces, and the British patents of Emile and Pierre Martin, No. 2,031, of 1864; No. 2,137, of 1865, and No. 859, of 1866, represent the so-called _Siemens-Martin_ process, which is the best known and generally used open hearth process. [Illustration: FIG. 256.--SIEMENS REGENERATIVE FURNACE.]