to prevent the leakage of gas. The contacts for conducting the current to the electrode are arranged at the upper end and wedged between the electrodes and a holder of cast steel. This holder, in its turn, is supported on a frame movable up and down between two guides placed on each side of the electrode.

In this process provision is made for a circulation of the gases in such manner that gas is drawn by means of a fan from the gas outlets and blown into

the crucible. Consequently, the quantity of gas passing any given section of the shaft can be varied within certain limits by varying the speed of the fan.

This circulation of gas has two special objects, namely, (a) The gas blown into the crucible is there heated and gives off its heat to the charge in the shaft in passing up through it. Through this heating of the charge in the shaft a reduction of the ore by CO is facilitated, so that this gas is utilized to some

extent for the process. (b) The second purpose of the circulation of the gas is connected with the construction of the crucible, as the gas cools the roof and thus protects it from overheating. This cooling action of the gas is due in part to the absorption of heat or raising the temperature of the gas and in part to the decomposition of CO2 and H2O in the gas in contact with the incandescent carbon in the crucible.

A diagram of the electrical connections is shown in figure 12.

FIGURE 10.--Sectional elevation of furnace at Trollhättan.

Operations with this furnace were started November 15, 1910, and were continued without interruption until May 29, 1911. During this period various kinds of ore were smelted, and such grades of acid and basic slags were produced as seemed best suited to the treatment of each particular ore. The furnace worked well from the start, and was closed down that such alterations might be made as experience had demonstrated would be beneficial, and also that the crucible 16282°-Bull. 67-14- 2

principal changes and additions that were made after the closing down of the furnace were as follows:

A system was installed for washing the gas which is returned to the crucible, so as to free the gas from dust particles before it reached the fan that caused the circulation,

might be relined and a new roof built, as the frequent alternation of acid and basic slags had damaged the brickwork of the crucible. The

FIGURE 11.-Sectional elevation of furnace at Trollhättan, showing arrangement of gas circulation.

FIGURE 12.-Diagram of electrical connections of furnace at Trollhättan. a, ammeters; b, electrodes; c, main switches; d, lightning arresters; e, induction coil; f, kilowatt meters; g, kilowatt-hour meters; h, maximum relay; j, switch; k, oil resistance; 7, automatic switches; m, clock control; n, fuses; o, p, q, transformers; v, voltmeters.

Electrode contact jackets were constructed and installed which permitted the electric current to be introduced to the electrodes at the point where they pass through the roof of the crucible rather than at the end of the electrode as was formerly done (fig. 10).

Round electrodes, 23§ inches in diameter, were substituted for square electrodes. The latter were built of four carbons, of about 12 by 12 inch section. The electrodes were threaded so as to permit their being joined by means of screw nipples, thus avoiding the waste of butt ends, as formerly, as soon as the electrodes became too short for further use.

SUMMARY OF WORKING RESULTS AND ANALYSES.

The following tables present in condensed form the results obtained by the operation of the furnace from November 15, 1910, to April 9, 1911:

TABLE 1.-Results of clectric iron smelting at Trollhättan, Sweden.