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.
