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A third type of furnace that is meeting with some extensive use is the Giroud, which, like the Heroult furnace, is based on the arc and resistance in principle, but in its construction has a number of different features.
But the idea by no means languished, and in 1899 Paul Heroult and other electro-metallurgists were active in developing a practical electric furnace for iron and steel work.
In the Heroult process the impurities of the molten iron are washed out by treatment with suitable slags. The furnace consists of a crucible in the form of a closed shallow iron tank, thickly lined with dolomite and magnazite brick, with a hearth of crushed dolomite.
One of the pioneer furnaces for this purpose which has seen considerable development and practical application is the Heroult furnace, which is a tilting furnace of the crucible type, whose operation depends upon both the heat of the arc and on the heat produced by the resistance of the molten material.
As the current passes horizontally from the upper electrodes through the slag and molten metal in the furnace chamber to the base electrodes of the furnace, it permits of the easy regulation of the arcs and the use of lower electromotive force, while there is only one arc in the path of the current instead of two as in the Heroult type.
It, however, has been improved recently and two rings of molten metal employed instead of one so that a wide centre trough is obtained in which the metal is subjected to ordinary resistance heat by direct or alternating currents. This furnace permits of various metallurgical operations and the elimination of impurities as in the Heroult type.
Several interesting subjects attracted much of my attention, by Henry Scheffer, Meissonnier, Bouchot, Dupré, Steuben, Rubio, Signol, Charlet, Storelli, and a few others; in water colours the French are now advancing with rapid strides, this year there were some exquisite specimens in that department of painting, particularly by Heroult: but the style in which the French now are most happy, is in what they call pastel, which consists in a great variety of coloured chalks, rather harder than what we understand by crayons; the manner in which they execute portraits about a quarter the size of life, with these materials, is surprising, it infinitely surpasses their oil portrait or their miniatures.
For three tons of steel eight to ten hours are required in the Heroult crucible furnace.
The application of electro- metallurgy at this time was confined to the manufacture of steel, as the smelting of iron had not emerged from the experimental stage of its development, though extensive trials on a large scale of various furnaces have been undertaken in Europe and by the Canadian government at Sault Ste. Marie, where the Heroult furnace, soon to be described, was employed.
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