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From the Earth to the Moon

Chapter 9. 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.
 
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