[Illustration: CLEANING CARS BY THE “VACUUM” METHOD.] The Open Hearth Process. Steel making by the open hearth process is chiefly due to the late Sir William Siemens. In a gas producer he gave his fuel the gaseous form, in which it is more easily controlled and more efficient than when solid. Of more importance were his regenerators, chambers of brickwork, heated by the products of combustion, and then employed to warm incoming currents of air and gas on their way to the furnace. The Siemens furnace has been modified in many ways and much improved in its details. A good example of an open hearth furnace, as planned by the late Mr. Bernard Dawson, is shown on page 165. It centers in a large hearth built of refractory materials, upon which the metal is melted as flames play over it. At each end are two regenerators filled with checker firebricks through which air or gas passes on its way to the furnace, and through which, at due intervals, the products of combustion emerge as they pass to the stack. On each side, one of the regenerators is for air, the other for gas; between them is a substantial wall to prevent any mixing before their currents reach the hearth. It is in the regenerator, which utilizes heat which otherwise would be wasted, that the open hearth displays its best feature. Its products vary in composition as its raw materials vary, whether pig-iron of a specific kind, a particular ore, or scrap; and just as in the Bessemer process, a harmful element, as phosphorus, is removed almost wholly by the addition of a suitable ingredient, such as lime. In excellence and uniformity of quality open hearth steels are preferred to those of the Bessemer converter, even for railroad rails which for years were made solely by the Bessemer process. [Illustration: Open hearth furnace.] The Gayley Dry-Blast Process.