"we must now take into consideration the metal to be employed.
Our cannon must be possessed of great tenacity, great hardness,
be infusible by heat, indissoluble, and inoxidable by the
corrosive action of acids."

"There is no doubt about that," replied the major; "and as we
shall have to employ an immense quantity of metal, we shall not
be at a loss for choice."

"Well, then," said Morgan, "I propose the best alloy hitherto
known, which consists of one hundred parts of copper, twelve of
tin, and six of brass."

"I admit," replied the president, "that this composition has
yielded excellent results, but in the present case it would be
too expensive, and very difficult to work. I think, then, that
we ought to adopt a material excellent in its way and of low
price, such as cast iron. What is your advice, major?"

"I quite agree with you," replied Elphinstone.

"In fact," continued Barbicane, "cast iron costs ten times less
than bronze; it is easy to cast, it runs readily from the moulds
of sand, it is easy of manipulation, it is at once economical of
money and of time. In addition, it is excellent as a material,
and I well remember that during the war, at the siege of
Atlanta, some iron guns fired one thousand rounds at intervals
of twenty minutes without injury."

"Cast iron is very brittle, though," replied Morgan.