STEEL.—Crucible.

855

the mould. The plug is withdrawn, and the toppart having been trimmed and loosened from themould by passing a knife between the clay andmould, it is placed upon a short pillar which pushesup the false bottom and sets the clay free. Thepots are then very slowly and carefully dried, andgradually annealed before use. They are taken hotfrom the annealing furnace to the melting furnace,where they are placed upon small lumps of similarmaterial to keep them off the bars of the grate.Covers or lids of fire clay (Fig. 4) protect the

conventional furnace. It differs from ours chiefly inthe following particulars, viz.:—Whereas it is cus-tomary to carry the products of combustion of eachfurnace direct into a flue, forming a chimney 14inches square and about 40 feet high, we, having tocombine the contents of many crucibles into onelarge casting, and wishing to avoid the obstructionof these chimney stacks, have connected manymelting holes into one common flue, with a chimneyoutside the building. Next, whereas common prac-tice covers the ‘cellar’ by a brick arch of from 10to 15 feet sjoan, beneath which the pots are made, wehave made iron floors, and make the pots in aseparate building.

contents of the pots from the fuel in which theyare heated.

The old form of crucible furnace was of verysimple construction, and is represented below (Figs.5, 6); as is also an improved coke furnace (Figs.7, 8) used at Vickers, Sons, and Co’s., and figuredin Hackney’s valuable paper on Steel in the “ Trans-actions of the Institute of Civil Engineers, ” vol xlii.,1874-75. E. Reynolds, who furnished IIackneywith these drawings, says—“ I have failed to find eitherhere or amongst our neighbours any drawing of the

Fig. 7.

Fig. 8.

“In England, I believe universally, the practiceis to use two pots in each melting hole, and theordinary charge for each pot is 50 lbs. for the firstround ; but we, having succeeded in producing verygood pots, commonly use 70-lb. pots, and on specialoccasions have used pots containing 100 lbs. Theordinary day’s work (in Sheffield) is three rounds,the charges being about 48 lbs. in the first round,44 lbs. in the second round, and 30 lbs in the thirdround; whereas we get about 66 lbs., 60 lbs., and50 lbs., respectively. The diminished charges inthe second and third rounds are due to the corrosionof the inside of the pot, at the level of the meltedmetal, from the action of the slag, technically called‘ flux,’ which lies on the surface of the metal, andwhich so far reduces the thickness of the pot that itwould not be safe to fill it so full a second time.

“ The first round takes about four hours to melt,the second three hours, and the third from two tothree hours, according to the temper of the steel