"In fact," resumed Barbicane, "cast-iron costs ten times less than bronze; it is easily melted, it is readily run into sand moulds, and is rapidly manipulated; it is, therefore, an economy of money and time. Besides, that material is excellent, and I remember that during the war at the siege of Atlanta cast-iron cannon fired a thousand shots each every twenty minutes without being damaged by it."
"Yet cast-iron is very brittle," answered Morgan.
"Yes, but it possesses resistance too. Besides, we shall not let it explode, I can answer for that."
"It is possible to explode and yet be honest," replied J.T. Maston sententiously.
"Evidently," answered Barbicane. "I am, therefore, going to beg our worthy secretary to calculate the weight of a cast-iron cannon 900 feet long, with an inner diameter of nine feet, and sides six feet thick."
"At once," answered J.T. Maston, and, as he had done the day before, he made his calculations with marvellous facility, and said at the end of a minute—
"This cannon will weigh 68,040 tons."
"And how much will that cost at two cents a pound?"
"Two million five hundred and ten thousand seven hundred and one dollars."
J.T. Maston, the major, and the general looked at Barbicane anxiously.