"Quite so," said the major. "What is the rule in such a case?"
"Ordinarily the length of a gun is 20 to 25 times the diameter of the shot, and its weight 235 to 240 times that of the shot."
"That is not enough," cried J. T. Maston impetuously.
"I agree with you, my good friend; and, in fact, following this proportion for a projectile nine feet in diameter, weighing 30,000 lbs., the gun would only have a length of 225 feet, and a weight of 7,200,000 lbs."
"Ridiculous!" rejoined Maston. "As well take a pistol."
"I think so too," replied Barbicane; "that is why I propose to quadruple that length, and to construct a gun of 900 feet."
The general and the major offered some objections; nevertheless, the proposition, actively supported by the secretary, was definitively adopted.
"But," said Elphinstone, "what thickness must we give it?"
"A thickness of six feet," replied Barbicane.
"You surely don't think of mounting a mass like that upon a carriage?" asked the major.
"It would be a superb idea, though," said Maston.
"But impracticable," replied Barbicane. "No; I think of sinking this engine in the earth alone, binding it with hoops of wrought iron, and finally surrounding it with a thick mass of masonry of stone and cement. The piece once cast, it must be bored with great precision, so as to preclude any possible windage. So there will be no loss whatever of gas, and all the expansive force of the powder will be employed in the propulsion."
"One simple question," said Elphinstone: "is our gun to be rifled?"
"No, certainly not," replied Barbicane; "we require an enormous initial velocity; and you are well aware that a shot quits a rifled gun less rapidly than it does a smooth-bore."
"True," rejoined the major.
The Committee here adjourned for a few minutes to tea and sandwiches.
On the discussion being renewed, "Gentlemen," said Barbicane, "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 inoxydable 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 100 parts of copper, 12 of tin, and 6 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 cost 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.
"Yes, but it possesses great resistance. I will now ask our worthy secretary to calculate the weight of a cast-iron gun with a bore of nine feet and a thickness of six feet of metal."
"In a moment," replied Maston. Then, dashing off some algebraical formulæ with marvellous facility, in a minute or two he declared the following result: —
"The cannon will weigh 68,040 tons. And, at two cents a pound, it will cost – ?"
"2,510,701 dollars."
Maston, the major, and the general regarded Barbicane with uneasy looks.
"Well, gentlemen," replied the president, "I repeat what I said yesterday. Make yourselves easy; the millions will not be wanting."
With this assurance of their president the Committee separated, after having fixed their third meeting for the following evening.
CHAPTER IX.
THE QUESTION OF THE POWDERS
There remained for consideration merely the question of powders. The public awaited with interest its final decision. The size of the projectile, the length of the cannon being settled, what would be the quantity of powder necessary to produce impulsion?
It is generally asserted that gunpowder was invented in the fourteenth century by the monk Schwartz, who paid for his grand discovery with his life. It is, however, pretty well proved that this story ought to be ranked amongst the legends of the middle ages. Gunpowder was not invented by any one; it was the lineal successor of the Greek fire, which, like itself, was composed of sulphur and saltpetre. Few persons are acquainted with the mechanical power of gunpowder. Now this is precisely what is necessary to be understood in order to comprehend the importance of the question submitted to the committee.
A litre of gunpowder weighs about 2 lbs.; during combustion it produces 400 litres of gas. This gas, on being liberated and acted upon by a temperature raised to 2400 degrees, occupies a space of 4000 litres: consequently the volume of powder is to the volume of gas produced by its combustion as 1 to 4000. One may judge, therefore, of the tremendous pressure of this gas when compressed within a space 4000 times too confined. All this was, of course, well known to the members of the committee when they met on the following evening.
The first speaker on this occasion was Major Elphinstone, who had been the director of the gunpowder factories during the war.
"Gentlemen," said this distinguished chemist, "I begin with some figures which will serve as the basis of our calculation. The old 24-pounder shot required for its discharge 16 lbs. of powder."
"You are certain of the amount?" broke in Barbicane.
"Quite certain," replied the major. "The Armstrong cannon employs only 75 lbs. of powder for a projectile of 800 lbs., and the Rodman Columbiad uses only 160 lbs. of powder to send its half-ton shot a distance of six miles. These facts cannot be called in question, for I myself raised the point during the depositions taken before the Committee of Artillery."
"Quite true," said the general.
"Well," replied the major, "these figures go to prove that the quantity of powder is not increased with the weight of the shot; that is to say, if a 24-pounder shot requires 16 lbs. of powder; – in other words, if in ordinary guns we employ a quantity of powder equal to two-thirds of the weight of the projectile, this proportion is not constant. Calculate, and you will see that in place of 333 lbs. of powder, the quantity is reduced to no more than 160 lbs."
"What are you aiming at?" asked the president.
"If you push your theory to extremes, my dear major," said J. T. Maston, "you will get to this, that as soon as your shot becomes sufficiently heavy you will not require any powder at all."
"Our friend Maston is always at his jokes, even in serious matters," cried the major; "but let him make his mind easy, I am going presently to propose gunpowder enough to satisfy his artillerist's propensities. I only keep to statistical facts when I say that during the war, and for the very largest guns, the weight of powder was reduced, as the result of experience, to a tenth part of the weight of the shot."
"Perfectly correct," said Morgan; "but before deciding the quantity of powder necessary to give the impulse, I think it would be as well – "
"We shall have to employ a large-grained powder," continued the major, "its combustion is more rapid than that of the small."
"No doubt about that," replied Morgan, "but it is very destructive, and ends by enlarging the bore of the pieces."
"Granted;