It has its parallel in the rising of the iron in a puddling-furnace at the close of the boil, a phenomenon with which every one is familiar who has watched a heat being boiled or puddled. That all of the iron does not run out of the puddling-furnace at this stage is owing to the fact that there is not heat enough in the puddling-furnace to keep the iron liquid after it has been decarbonized.
During the running of a basic open-hearth furnace an apparently dead heat was tapped; before the steel reached the ladle there was a sort of explosion; the steel was blown all over the shop, the men had to run for their lives, and not one tenth of the steel reached the ladle. The manager was rated roundly for carelessness in not having dried his spout, and the incident closed. A few days later another quiet heat was tapped and it ran into the ladle; about the time the ladle was full the steel rose rapidly, like a beaten egg or whipped cream, and ran out on to the floor, cutting the sides of the ladle, the ladle-chains, and the crane-beams as it flowed. The men ran, and there was no injury to the person.
Again the manager was blamed, this time for having a damp ladle, and he was notified of an impending dismissal if such a thing occurred again. He protested that he knew the ladle and the stopper were red-hot, that he had examined them personally and carefully, and knew he stated the truth.
There were several reasons for looking into the matter farther: first, the man in charge was known to be truthful and careful, so that there was no reason for doubting his word; second, if the vessel and rod were red-hot, there could be no aqueous moisture there; and, finally, such an ebullition from dampness was contrary to experience, as a small quantity of water under a mass of molten iron, or slag, results almost invariably in a violent explosion, like that of gunpowder or dynamite.
Upon inquiry it was found that prior to both ebullitions there had been a large hole in the furnace-bottom, requiring about a peck of material to fill it in each case. Magnesite was used; the magnesite was bought raw, and burned in the place. It is well known that it takes a long time and high heat to drive carbonic acid out of magnesite, and it was surmised that insufficient roasting might have caused the trouble. Samples of burned and of raw magnesite were sent to the laboratory, and the burned was found to contain about as much carbonic acid as the raw magnesite. Then the case seemed clear: This heavily charged magnesite was packed into the hole; the heat was charged and melted. The magnesite held the carbonic acid until near the close of the operation; then the intense heat of the steel forced the release of the gas, which was at once absorbed by the steel. Owing to the superincumbent weight of the steel the gas was absorbed quietly, and when the weight was removed the gas escaped, exactly as it does at the close of puddling or in the frothing of yeast.
Whether the carbonic acid remained such, or whether it took up an equivalent of carbon and became carbonic oxide, and then again took up oxygen from the bath, and so kept on increasing in volume, is not known.
The facts seem clear, and the collateral proof is that thorough burning of the magnesite, and of any dolomite that was used, prevented a recurrence of any such accidents.
Such ebullitions have occurred and caused the burning to death of pitmen, and the statement of the above case may be of use to melters in the future who have not met such an experience.
OXYGEN AND NITROGEN.
Oxygen and nitrogen are present in all steel and both are injurious, probably the most so of all impurities.