From the Earth to the Moon
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Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 Next page "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. "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 formulae with marvelous 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----" "Two million five hundred and ten thousand seven hundred and one 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 among 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 sulfur and saltpeter. 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 two pounds; during combustion it produces 400 litres of gas. This gas, on being liberated and acted upon by temperature raised to 2,400 degrees, occupies a space of 4,000 litres: consequently the volume of powder is to the volume of gas produced by its combustion as 1 to 4,000. One may judge, therefore, of the tremendous pressure on this gas when compressed within a space 4,000 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 sixteen pounds of powder." "You are certain of this amount?" broke in Barbicane. "Quite certain," replied the major. "The Armstrong cannon employs only seventy-five pounds of powder for a projectile of eight hundred pounds, and the Rodman Columbiad uses only one hundred and sixty pounds 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 sixteen pounds 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 three hundred and thirty-three pounds of powder, the quantity is reduced to no more than one hundred and sixty pounds." "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 the 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 looked 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 pounds 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 pounds 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 pounds of powder will create 6,000,000,000 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?" |
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