For a few years the induction furnace was developed as rapidly as the arc furnace, but during the past three years its use has not increased as rapidly. The reason for this will be discussed later.

PRESENT STATUS OF THE ELECTRIC STEEL INDUSTRY.

In 1904 there were 4 electric furnaces being used in Europe for the manufacture of steel, whereas to-day there are 114 electric furnaces producing steel in Europe and the United States and 30 others are in course of construction. As in other electrothermic processes, development has not been so rapid in the United States as in Europe. Only 14 furnaces are in this country. The average capacity per charge of the furnaces already built is 3.7 tons, whereas that of the furnaces under construction is 4.5 tons, an increase of 21.6 per cent. The total charge capacity of the furnaces now installed is about 250 tons per charge, and the total charge capacity of the furnaces under construction will be 170 tons per charge. The arc furnaces vary in capacity from 1 to 15 tons and require from 200 to 1,500 kw. for operation. A Héroult furnace of 25-ton capacity, requiring 3,000 kw., is nearly completed at Bruckhausen, Germany. The induction furnaces vary in capacity from 1 to 10 tons and require from 165 to 600 kw. for operation.

Of the 114 furnaces in operation 84 are arc furnaces and 30 are induction furnaces; of the 30 under construction, 26 are arc furnaces and 4 induction furnaces.

The following table gives the annual production of steel in electric furnaces, by countries, for the years 1908 to the first half of 1912.

From Table 1 it may be seen that for a new process in so conservative an industry as iron and steel manufacture, progress has been very rapid since 1908. Germany leads all countries in the steady growth of the process and the total tonnage produced. Although in Germany the production of electric-furnace steel increased 67.8 per cent in 1911, in the United States it decreased 44.2 per cent. The decrease in this country was probably due to the conservatism of American steel makers, which has prevented the wide adoption of the process before experimental results have conclusively proved its merits. From present indications there will be a considerable increase in the production of electric-furnace steel in this country in the near future, although a very small tonnage, 6,882 tons, was reported by the American Iron and Steel Institute as the output for the first half of 1912. Of the total production of electric-furnace steel in the United States in 1911, 27,227 tons were ingots and 1,878 tons castings. Of the total tonnage of electric-furnace steel made here in 1911, 6,700 tons were alloy steel and 462 tons were rolled into rails. The large production of steel in the United States and Germany in proportion to the number of furnaces operating is due to the use of molten Bessemer and open-hearth steel instead of cold scrap. The use of the latter almost entirely accounts for the comparatively small tonnage produced by France in proportion to the number of furnaces in operation. No figures were obtained for England, but it is probable that at least 10,000 tons of electric-furnace steel is manufactured in England. It is estimated that about 12 furnaces operate there, several of which receive hot-metal charges. Italy, Norway, Switzerland, Belgium, and Russia produce small tonnages also. The slight increase in the total electric-furnace steel production for 1911 over that produced in 1910 was caused by the big decrease in production in the United States.

In the first years of its development the electric process was considered as a competitor of the crucible process only for making highclass steel from scrap iron and scrap steel; but with the successful operation of larger furnaces the electric process is likely to become an important adjunct to the Bessemer and open-hearth processes as a means of superrefining the molten products that they yield. The electric process, however, does not appear to be destined to supersede either of these methods, as greater efficiency and economy are obtained by a combination of any two of the three processes as a duplex process. The success of recent experiments has obtained for the electric process a definite place as a superrefining method. In time preliminary refining will probably be done mainly in the Bessemer converter, the process being finished in the electric furnace or the open hearth. In Europe the electric-furnace process for making steel

a Iron Age, The world's output of electric steel; vol. 91, 1913, p. 304.

of the highest grades is rapidly superseding the old crucible method, because of its greater economy of operation and the possibility of using materials of lower grade.

ELECTRIC STEEL FURNACES.

In general electric furnaces in commercial use for the manufacture of steel may be divided into two groups-arc furnaces and induction furnaces. In the arc furnace the heating is caused by the arc, which may be between the electrode and the bath, or between two or more electrodes so arranged as to heat the metal by radiation only. In the induction furnace the heat is supplied by a current induced in the bath. The operation is similar to that of a step-down transformer, having a large number of primary turns and a single secondary turn, which is formed by the steel in the furnace.

ARC FURNACES.

THE HÉROULT FURNACE.

The Héroult electric steel furnace heads the list of electric furnaces in use in the iron and steel industry with 31 furnaces already built and 20 others in course of construction. The wide use of the Héroult furnace is due chiefly to its efficiency, simplicity of construction, and adaptability to many different uses. Also it was the pioneer electric steel furnace.

SINGLE-PHASE HÉROULT FURNACE.

The design of the 2-ton, single-phase Héroult furnace has changed little from that (fig. 18) of the first Héroult furnace, which has been in operation at La Praz, France, continuously since 1900. The furnace consists of a shallow hearth of dolomite, similar to the open hearth, incased in a steel shell, and covered with a roof of silica brick. The 2-ton Heroult furnace at Braintree, England, has the pouring spout in the center of one side, and two doors, one on each end of the furnace. There are two 14-inch carbon electrodes projecting into the furnace through the roof and held in place by a steel framework extending from the rear over the roof. The electric current arcs between each of the electrodes, which are connected in series, and the bath, thus passing through the bath. The Braintree furnace is operated with 300-kw. 25-cycle alternating current at 100 volts. The furnace is set on curved steel bars, the whole being on a concrete foundation, and is tilted by rotating a screw, operated by a 5-kw. electric motor. Springs are used on the bottom to keep the furnace from creeping.

The exterior of the 2-ton furnace is 5 feet 6 inches wide, 7 feet 6 inches long, 4 feet 9 inches high to the top of the roof, and 9 feet

3 inches high to the top of the electrode holders. The furnace foundation is 2 feet 6 inches above the main floor of the foundry. The whole furnace is incased in plate steel inch thick.

In lining the furnace a mixture of tar and dolomite is tamped in around a sectional mold to a depth of 9 inches to form the bottom. The sides of the hearth slope about 60 degrees up to about 18 inches above the bottom. From here up to the roof, 15 inches, the lining is magnesite brick. The lining is 12 inches thick on the sides and 14 inches thick on the ends. The internal dimensions of the furnace are 4 feet 2 inches by 1 foot 8 inches at the bottom of the hearth, and 5 feet by 2 feet 7 inches at the top, with a depth of 31 inches. The doors are 9 by 10 inches. The customary roof for this type of furnace is silica brick, set so as to give a roof 12 inches thick. At Braintree considerable difficulty has been experienced with the roof and several kinds of brick have been tried, such as silica, magnesite, and bauxite. Bauxite brick were being used recently.

The electrodes are threaded for continuous feeding and are used in either 4 or 6 foot sections. Each of the two electrode holders consists of two vertical 9-inch channel irons that are set 5 inches apart and act as guides for two 3-inch copper plates. These vertical copper plates are attached to a heavy horizontal copper plate that extends over the furnace and has a clamp tightened by a screw for supporting the electrodes. The electrodes may be raised or lowered by hand wheels at the rear or by automatic Thury regulators. In later furnaces the copper, that serves to support the electrode as well as conduct the current, is to be replaced by manganese steel supports and copper bus bars large enough to conduct the current. This will strengthen the holder and reduce the amount of copper, about 1 ton being necessary in the old design. The electrode holders are water cooled at the electrodes, and there are copper water jackets around the electrodes where they enter the roof.

The cost of a 2-ton Héroult electric steel furnace may be estimated as follows:

The furnace, automatic regulators, platform, transformers, switchboard, and other equipment will cost when completely installed about $12,000 to $15,000, exclusive of crane or buildings; allow an engineering fee of $5,000, and $350 per month and expenses for an expert to establish the operation of the furnace, making a total of about $25,000. The royalty on tool steel produced would be from $1 to $3 per ton according to quantity, and on castings, billets, or ingots 50 cents per ton.

THREE-PHASE HÉROULT FURNACE.

With the use of three-phase electric current in the Héroult furnace of 15 tons capacity a slightly modified design has been made. Until