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366 ^ METALLURGY OF CAST IRON.
blast can often be supplied from a blacksmith's forge fan. Should it be desirable to run steadily all day for crucible work, the breast should be dug out about twice during the "heat," and the ash and dross pulled out, so as to leave room for clean fuel. In making the breast for crucible work, have it formed of a sand that will not bake or cake hard and larger than shown. This will permit its being dug out readily.
Should it not be desired to use the device as a combination furnace and cupola, but strictly for crucible work, we would advise sinking the same in a pit, and instead of using the regular cupola drop bottom, which goes with this device, have the bottom consist of a regular grate, with an ash pit six inches deep, the diameter of the grate. Have the ash pit closed air-tight, and instead of admitting the blast into the body of the furnace, as is done with the cupola here shown, let it pass into the ash pit and enter the furnace through the grates. By having a pit three feet by five feet and three feet deep the combination cupola and furnace could be lowered to bring the staging line H level with the floor. This would make it more convenient for charging, or lifting a crucible in or out, and by having a handy step-ladder, ready access can be had to the pit for "tapping out" or cleaning the "dump." For raising a pot of metal up to the floor, employ a pair of tongs similar to those used for lifting a crucible out. The flue A should be lined with fire brick or clay for any distance the outer shell could be heated red hot were it not lined. This flue should be well bound with stays to prevent the heat cracking it open.
As very few founders have had opportunity for experience in crucible work, we will detail more pointsbe found a cheap temporary arrangement for melting from fifty to one hundred pounds of iron, Ferrochrom.