From the Earth to the Moon, Direct in Ninety-Seven Hours and Twenty Minutes: and a Trip Round It
Page 11
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 theprojectile, the length of the cannon being settled, what would be thequantity of powder necessary to produce impulsion?
It is generally asserted that gunpowder was invented in the fourteenthcentury by the monk Schwartz, who paid for his grand discovery with hislife. It is, however, pretty well proved that this story ought to beranked amongst the legends of the middle ages. Gunpowder was not inventedby any one; it was the lineal successor of the Greek fire, which, likeitself, was composed of sulphur and saltpetre. Few persons are acquaintedwith the mechanical power of gunpowder. Now this is precisely what isnecessary to be understood in order to comprehend the importance of thequestion submitted to the committee.
A litre of gunpowder weighs about 2 lbs.; during combustion it produces400 litres of gas. This gas, on being liberated and acted upon by atemperature raised to 2400 degrees, occupies a space of 4000 litres:consequently the volume of powder is to the volume of gas produced byits combustion as 1 to 4000. One may judge, therefore, of the tremendouspressure of this gas when compressed within a space 4000 times tooconfined. All this was, of course, well known to the members of thecommittee when they met on the following evening.
The first speaker on this occasion was Major Elphinstone, who had beenthe director of the gunpowder factories during the war.
Illustration: THE INVENTION OF GUNPOWDER BY THE MONK SCHWARTZ.
"Gentlemen," said this distinguished chemist, "I begin with some figureswhich will serve as the basis of our calculation. The old 24-pounder shotrequired 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 only75 lbs. of powder for a projectile of 800 lbs., and the Rodman Columbiaduses only 160 lbs. of powder to send its half-ton shot a distance of sixmiles. These facts cannot be called in question, for I myself raised thepoint 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 quantityof 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 inordinary guns we employ a quantity of powder equal to two-thirds of theweight of the projectile, this proportion is not constant. Calculate,and you will see that in place of 333 lbs. of powder, the quantity isreduced 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 sufficientlyheavy 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 presentlyto propose gunpowder enough to satisfy his artillerist's propensities.I only keep to statistical facts when I say that during the war, and forthe very largest guns, the weight of powder was reduced, as the resultof experience, to a tenth part of the weight of the shot."
"Perfectly correct," said Morgan; "but before deciding the quantity ofpowder 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, andends by enlarging the bore of the pieces."
"Granted; but that which is injurious to a gun destined to perform longservice 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 inorder that its mechanical effect may be complete."
"We must have," said Maston, "several touch-holes, so as to fire it atdifferent points at the same time."
"Certainly," replied Elphinstone; "but that will render the working ofthe piece more difficult. I return then to my large-grained powder, whichremoves those difficulties. In his Columbiad charges Rodman employed apowder as large as chestnuts, made of willow charcoal, simply dried incast-iron pans. This powder was hard and glittering, left no trace uponthe hand, contained hydrogen and oxygen in large proportion, took fireinstantaneously, and, though very destructive, did not sensibly injurethe mouth-piece."
Up to this point Barbicane had kept aloof from the discussion; he leftthe others to speak while he himself listened; he had evidently got anidea. He now simply said, "Well, my friends, what quantity of powder doyou 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 brokenby the president.
"Gentlemen," he quietly said, "I start from this principle, that theresistance of a gun, constructed under the given conditions, is unlimited.I shall surprise our friend Maston, then, by stigmatizing his calculationsas 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; foryou 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 enoughfor 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 ofpowder, while preserving to it its mechanical power."
"Good; but by what means?"
"I am going to tell you," replied Barbicane quietly. "Nothing is moreeasy than to reduce this mass to one quarter of its bulk. You know thatcurious cellular matter which constitutes the elementary tissues ofvegetables? This substance is found quite pure in many bodies, especiallyin cotton, which is nothing more than the down of the seeds of the cottonplant. Now cotton, combined with cold nitric acid, becomes transformedinto a substance eminently insoluble, combustible, and explosive. It wasfirst discovered in 1832, by Braconnot, a French chemist, who called itxyloidine. In 1838 another Frenchman, Pelouze, investigated its differentproperties, and finally, in 1846, Schonbein, Professor of Chemistry atBale, proposed its employment for purposes of war. This powder, nowcalled pyroxyle, or fulminating cotton, is prepared with great facilityby simply plunging cotton for fifteen minutes in nitric acid, thenwashing 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 ignitesat 170 degrees in place of 240, and its combustion is so rapid that onemay set light to it on the top of ordinary powder, without the latterhaving 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 tothat of gunpowder. I will even add, that if we mix with it one-eighthof its own weight of nitrate of potass, its expansive force is againconsiderably 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; andsince we can, without danger, compress 500 lbs. of cotton into 27 cubicfeet, the whole quantity will not occupy a height o
f more than 180 feetwithin the bore of the Columbiad. In this way the shot will have morethan 700 feet of bore to traverse under a force of 6,000,000,000 litresof gas before taking its flight towards the moon."
At this junction J. T. Maston could not repress his emotion; he flunghimself 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 inexecution.
"A mere matter of detail, a bagatelle," said J. T. Maston.
Illustration: CAPTAIN NICHOLL