CHAPTER VIII.
HISTORY OF THE CANNON

The resolutions passed at the last meeting produced a great effect out of doors. Timid people took fright at the idea of a shot weighing 20,000 lbs. being launched into space; they asked what cannon could ever transmit a sufficient velocity to such a mighty mass. The minutes of the second meeting were destined triumphantly to answer such questions. The following evening the discussion was renewed.

"My dear colleagues," said Barbicane, without further preamble, "the subject now before us is the construction of the engine, its length, its composition, and its weight. It is probable that we shall end by giving it gigantic dimensions; but however great may be the difficulties in the way, our mechanical genius will readily surmount them. Be good enough, then, to give me your attention, and do not hesitate to make objections at the close. I have no fear of them. The problem before us is how to communicate an initial force of 12,000 yards per second to a shell of 108 inches in diameter, weighing 20,000 lbs. Now when a projectile is launched into space, what happens to it? It is acted upon by three independent forces, the resistance of the air, the attraction of the earth, and the force of impulsion with which it is endowed. Let us examine these three forces. The resistance of the air is of little importance. The atmosphere of the earth does not exceed forty miles. Now, with the given rapidity, the projectile will have traversed this in five seconds, and the period is too brief for the resistance of the medium to be regarded otherwise than as insignificant. Proceeding, then, to the attraction of the earth, that is, the weight of the shell, we know that this weight will diminish in the inverse ratio of the square of the distance. When a body left to itself falls to the surface of the earth, it falls five feet in the first second; and if the same body were removed 257,542 miles farther off, in other words, to the distance of the moon, its fall would be reduced to about half a line in the first second. That is almost equivalent to a state of perfect rest. Our business, then, is to overcome progressively this action of gravitation. The mode of accomplishing that is by the force of impulsion."

"There's the difficulty," broke in the major.

"True," replied the president; "but we will overcome that, for this force of impulsion will depend upon the length of the engine and the powder employed, the latter being limited only by the resisting power of the former. Our business, then, to-day is with the dimensions of the cannon."

"Now, up to the present time," said Barbicane, "our longest guns have not exceeded twenty-five feet in length. We shall therefore astonish the world by the dimensions we shall be obliged to adopt. It must evidently be, then, a gun of great range, since the length of the piece will increase the detention of the gas accumulated behind the projectile; but there is no advantage in passing certain limits."

"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; but that which is injurious to a gun destined to perform long service is not so to our Columbiad. We shall run no danger of an explosion; and it is necessary that our powder should take fire instantaneously in order that its mechanical effect may be complete."

"We must have," said Maston, "several touch-holes, so as to fire it at different points at the same time."

"Certainly," replied Elphinstone; "but that will render the working of the piece more difficult. I return then to my large-grained powder, which removes those difficulties. In his Columbiad charges Rodman employed a powder as large as chestnuts, made of willow charcoal, simply dried in cast-iron pans. This powder was hard and glittering, left no trace upon the hand, contained hydrogen and oxygen in large proportion, took fire instantaneously, and, though very destructive, did not sensibly injure the mouth-piece."

Up to this point Barbicane had kept aloof from the discussion; he left the others to speak while he himself listened; he had evidently got an idea. He now simply said, "Well, my friends, what quantity of powder do you propose?"

The three members look at one another.

"Two hundred thousand pounds," at last said Morgan.

"Five hundred thousand," added the major.

"Eight hundred thousand," screamed Maston.

A moment of silence followed this triple proposal; it was at last broken by the president.

"Gentlemen," he quietly said, "I start from this principle, that the resistance of a gun, constructed under the given conditions, is unlimited. I shall surprise our friend Maston, then, by stigmatizing his calculations as timid; and I propose to double his 800,000 lbs. of powder."

"Sixteen hundred thousand pounds?" shouted Maston, leaping from his seat.

"Just so."

"We shall have to come then to my ideal of a cannon half a mile long; for you see 1,600,000 lbs. will occupy a space of about 20,000 cubic feet; and since the contents of your cannon do not exceed 54,000 cubic feet, it would be half full; and the bore will not be more than long enough for the gas to communicate to the projectile sufficient impulse."

"Nevertheless," said the president, "I hold to that quantity of powder. Now, 1,600,000 lbs. of powder will create 6,000,000,000 of litres of gas. Six thousand millions! You quite understand?"

"What is to be done then?" said the general.

"The thing is very simple; we must reduce this enormous quantity of powder, while preserving to it its mechanical power."

"Good; but by what means?"

"I am going to tell you," replied Barbicane quietly. "Nothing is more easy than to reduce this mass to one quarter of its bulk. You know that curious cellular matter which constitutes the elementary tissues of vegetables? This substance is found quite pure in many bodies, especially in cotton, which is nothing more than the down of the seeds of the cotton plant. Now cotton, combined with cold nitric acid, becomes transformed into a substance eminently insoluble, combustible, and explosive. It was first discovered in 1832, by Braconnot, a French chemist, who called it xyloidine. In 1838 another Frenchman, Pelouze, investigated its different properties, and finally, in 1846, Schonbein, Professor of Chemistry at Bâle, proposed its employment for purposes of war. This powder, now called pyroxyle, or fulminating cotton, is prepared with great facility by simply plunging cotton for fifteen minutes in nitric acid, then washing it in water, then drying it, and it is ready for use."

"Nothing could be more simple," said Morgan.

"Moreover, pyroxyle is unaltered by moisture – a valuable property to us, inasmuch as it would take several days to charge the cannon. It ignites at 170 degrees in place of 240, and its combustion is so rapid that one may set light to it on the top of ordinary powder, without the latter having time to ignite."

"Perfect!" exclaimed the major.

"Only it is more expensive."

"What matter?" cried J. T. Maston.

"Finally, it imparts to projectiles a velocity four times superior to that of gunpowder. I will even add, that if we mix with it one-eighth of its own weight of nitrate of potass, its expansive force is again considerably augmented."

"Will that be necessary?" asked the major.

"I think not," replied Barbicane. "So, then, in place of 1,600,000 lbs. of powder, we shall have but 400,000 lbs. of fulminating cotton; and since we can, without danger, compress 500 lbs. of cotton into 27 cubic feet, the whole quantity will not occupy a height of more than 180 feet within the bore of the Columbiad. In this way the shot will have more than 700 feet of bore to traverse under a force of 6,000,000,000 litres of gas before taking its flight towards the moon."

At this junction J. T. Maston could not repress his emotion; he flung himself into the arms of his friend with the violence of a projectile, and Barbicane would have been stove in if he had not been bomb-proof.

This incident terminated the third meeting of the Committee.

Barbicane and his bold colleagues, to whom nothing seemed impossible, had succeeded in solving the complex problems of projectile, cannon, and powder. Their plan was drawn up, and it only remained to put it in execution.

"A mere matter of detail, a bagatelle," said J. T. Maston.