a to and fro motion through a crank, and a lateral motion through a screw and wormwheel gearing; this double motion enables it to be worked over the whole bed. The machine is bolted to the back of the casing, on the working side of the furnace, and by means of a fast and loose pulley may be put in and out of gear at will.

Danks' furnace. This furnace Fig. 36 consists of a cast-iron cylinder with conical ends, 4 feet long and

5 feet 3 inches in greatest diameter, bound with iron hoops. The shell is formed of segments bolted together, and on the inside are twelve radial ribs which keep the fettling in position. The cylinder is encircled at either end with a roller way which rests on anti-friction rollers. One end of the chamber is open to the fire-place, and the other end opens into an elbow-shaped moveable flue B leading to the chimney. The front conical cover has a tap-hole for slag, and the charge is withdrawn at the chimney-end by removing the moveable flue. The fireplace has an air-blast C, placed below the grate for increasing the combustion, and also small twyers in the back wall, through which air is blown at the level of the firebridge. The fire-bridge is hollow, being kept cool by a

current of water, and fettled on the inside. The chamber is first lined with a mixture of crushed iron-ore and lime, made into a mortar, which is then dried by a wood fire made inside. Then on this initial lining, is melted some iron-ore and hammer-slag, and into this, when liquid, are thrown pieces of "ilmenite" or harder ore, until the lining is studded with such pieces projecting from two to six inches. About 2 tons of ore are required for fettling a 700 lbs. furnace.

The charge of pig-iron is introduced at the chimneyend with 20 per cent. of cinder, and as it melts the furnace is made to slowly revolve, so that the iron is continually exposed to the action of the air in all parts. The action is the same as in ordinary puddling. The speed is gradually increased as the operation proceeds, and when the particles of iron begin to adhere the speed is again reduced to two revolutions per minute. The iron is collected into one large ball, and removed at the flue end by a forked lever carried by a crane. The time required for working a charge varies from 1 hour to 11⁄2 hours, accordingly as white or grey iron is used. Eight to ten charges may be worked for one fettling, with the consumption of 22 cwts. of coal per ton of iron. The oxidation of the impurities is chiefly effected by the oxides of iron in the fettling, and their removal is more perfect than by hand-puddling. A certain portion of the oxide of iron in the fettling is also reduced, so that one ton of puddled iron is obtained from 18 cwts. of pig-iron employed.

The disadvantages of the process are:-that a large mass of 700 lbs. weight has to be hammered or squeezed, requiring special appliances; the slag is difficult to remove completely from the interior of the mass; the wear and tear is very great, requiring frequent repairs; and the lining very soon wears away. Mr. J. Williams describes the furnace thus: "As a worker of metals it is without an equal; as a melter it is inferior to many;

as to endurance it is the shortest lived of any; and as to convenience of repairs it is one of the most difficult."

Crampton's furnace.-Mr. Crampton has introduced a revolving furnace Fig. 37, similar to that of Danks, with a double casing, through which water circulates so as to preserve the lining. The essential point of this furnace is the use of finely divided fuel as the source of heat. The ordinary fire is replaced by a tube-piece

t, fitted into the end plate of the moveable flue-piece; it is bell-mouthed towards the flue, and through this tube a stream of fine coal, mixed with the necessary amount of air, is injected automatically. Fig. 38 shows the feeding arrangement. The fuel is perfectly consumed. owing to its intimate admixture with air, producing a high and regular temperature.

Pernot's furnace.-M. Pernot at St. Chamond uses a furnace Fig. 39 with a fixed roof and circular turning bed, inclined at an angle of 5 or 6°. It consists of three parts; the fire-place burning ordinary fuel, or a gas-producer for generating gaseous fuel; the puddling-chamber with moveable bed; and the flue leading to the chimney. Fig. 39 represents a Pernot furnace heated with gaseous fuel. The bed is made of hollow wrought iron segments,

and fettled in the usual way with oxide of iron and cinder. Below the bed is a strong iron carriage moving on rails. This carriage has two pairs of wheels, and upon the framework is mounted the socket of the revolving axis of the bed. Rotation is imparted by means of an endless screw and worm wheel, which is fixed to the circumference of the ring at the bottom of the bed. Conical friction-rollers are also provided to assist the central pivot in keeping the hearth in position as it rotates.

Fig. 39.

From 15 to 20 cwts. of pig-iron with some scrap iron are introduced, after having been previously heated to redness. The charge is rapidly melted, and when the refining is completed, the iron is balled up by workmen. From 9 to 10 charges are worked off every 24 hours. The inclination of the bed causes the lining to be alternately under the molten iron and exposed to the flame, so that the bottom heat is constantly renewed and sticking of the charge prevented. Moreover, the exposure of the lining at each rotation favours oxidation, so that any FeO which has been reduced by the carbon of the pig-iron, is again converted into Fe3O4. The rotation not only rabbles, but promotes the reaction of the lining on the pig-iron. The disadvantages of this method are:great initial cost, the large quantity of fettling used, and the rapid wear of the bed, while the manual labour required is the same as in an ordinary furnace, although the work is much less fatiguing. The advantages are:-the large increase of metal refined in a given time, with a great economy of fuel, which is its principal advantage. The bed being removeable, the roof is readily accessible for repairs, and a new bed can be run under and worked while the old one is being mended.

:-the

Gas-furnaces for puddling. By the use of gasproducers, fuel may be used which is too inferior for ordinary furnaces and a higher temperature obtained by the combustion of the gas formed, than by using solid fuel directly. The puddling operation is the same as usual, except in such arrangements as Pernot's, where gas may be used in combination with mechanical puddling. In the case of Siemens' furnace, the regenerators are liable to be choked with dust, slag, and iron, carried over during the boiling stage. This may be largely remedied by passing the waste gases through an intermediate chamber, so as to deposit the solid matter before entering the regenerators. In some cases certain ferruginous substances have been placed at the entrance of the regenerators to act as a kind of filter. The difficulties arising from the deposition of dust, etc., have prevented the use of gas in many forges. The extreme heat produced in Siemens' furnace probably increases. the affinity of iron for carbon, which renders the fining difficult, and tends to produce an imperfect, steely iron.

The system of heating on the regenerative principle was developed by Sir William Siemens, and so named by Stirling, the originator of the principle, because the waste heat was restored again to the furnace. The regenerators are chambers of open refractory brickwork, built in pairs, two pairs being required for each furnace, each pair being used alternately for absorbing the heat of the gaseous products from the furnace and heating the gas and air required for combustion. Fig. 40 shows the furnace in vertical section with the regenerators beneath the bed. The larger chamber in each pair is used for heating the air and the smaller for heating the gas. By means of a reversing valve the waste gases pass to the right or left pair at will. When the waste gases are passing down through the right pair, the cold air and gas are passing up through the left pair, the direction being reversed when sufficient heat has been absorbed. The ratio of gas-space