The casting was to take place at twelve o'clock precisely. The previous evening each furnace had been charged with 114,000 pounds weight of metal in bars disposed cross-ways to each other, so as to allow the hot air to circulate freely between them. At daybreak the 1,200 chimneys vomited their torrents of flame into the air, and the ground was agitated with dull tremblings. As many pounds of metal as there were to cast, so many pounds of coal were there to burn. Thus there were 68,000 tons of coal which projected in the face of the sun a thick curtain of smoke. The heat soon became insupportable within the circle of furnaces, the rumbling of which resembled the rolling of thunder.The powerful ventilators added their continuous blasts and saturated with oxygen the glowing plates. The operation, to be successful, required to be conducted with great rapidity. On a signal given by a cannon-shot each furnace was to give vent to the molten iron and completely to empty itself. These arrangements made, foremen and workmen waited the preconcerted moment with an impatience mingled with a certain amount of emotion. Not a soul remained within the enclosure. Each superintendent took his post by the aperture of the run.