It appears that the weight of gas generated is equal to three tenths of the weight of the powder which yielded it, Volume of gas evolved.and that its bulk when cold, and expanded to the rarity of Common air was 240 times that of the powder; the barometer standing at about 30 inches. From this Robins concluded that if the fluid occupied a space equal to the volume of the gunpowder, its elastic force, when cold, would be 240 times the pressure of the atmosphere, when the barometer stands as above. Heat of gas evolved.Mr. Robins also considered that the heat evolved was at least equal to that of red hot iron, and he found by experiments that air heated to this temperature had its elasticity quadrupled, and therefore, that the force of gas from powder is at least four times 240 = 960, or in round numbers 1,000 times as great as the elasticity of the air measured by its pressure on an equal extent of surface. Pressure of gas generated.From the height of the barometer it is known that the pressure of the atmosphere is about 143⁄4lbs. upon the square inch, so that the pressure of the elastic gas generated by the combustion of the gunpowder upon the same area would be 14.75 by 1,000 or 14,750lbs. at the moment of explosion. Strength of powder not affected by density of air, but by damp.He found that the strength of Gunpowder was the same whatever might be the density of the atmosphere, but that the moisture of the air effected it considerably, in fact that the same quantity of powder which would give a bullet an initial velocity of 1,700 feet per second on a day when the atmosphere was comparatively dry, would upon a damp day give no more than 1,200 or 1,300 feet.
Velocity of gas
The velocity of the expansion of the gas is a most important point, upon which depends, chiefly, the peculiar value of the substance as a propelling agent. Many of the warlike machines of the Ancients produced a momentum far surpassing that of our heaviest cannon, but the great celerity given to the bodies projected from guns by gunpowder cannot be in the least approached by any other means than by the sudden production of an elastic gas. Mr. Robins found that the flame of gunpowder expanded itself when at the muzzle of the gun with a velocity of 7,000 feet per second.
Dr. Hutton’s calculation as to:—Volume, Temperature, Pressure.
It has been calculated that one cubic inch of powder is converted into 250 cubic inches of gas at the temperature of the atmosphere, and Dr. Hutton states that the increase of volume at the moment of ignition cannot be less than eight times; therefore one inch of gunpowder, if confined, at the time of explosion exerts a pressure of about 30,000lbs. being 250 by 8 by 15 = 30,000lbs. on the cubic inch, or 5,000lbs. on the square inch; and which at once accounts for its extraordinary power. TemperatureThe value of the temperature to which the gases are raised, on the explosion of the powder, has been variously estimated and it may be concluded to rise as high as will melt copper, or 4,000° Fahrenheit. Expansion.All gases expand uniformly by heat, the expansion having been calculated with great precision, to be 1⁄480th for each degree of Fahrenheit. If therefore we take Dr. Hutton’s calculations of one volume of powder expanding into 250 volumes of gas at the temperature of the atmosphere, and if we suppose 4,000° Fahrenheit to be the heat to which they are raised on ignition, the expansion of gunpowder would be calculated. How to calculate expansionThus, suppose the gas to be at 60°, the temperature of the atmosphere, we must deduct 60° from 4,000°, which will give 3,940, being the number of degrees remaining to which it is raised, hence temp.1° : vol.1480 temp.3,940° : vol.3940480 = vol.8·2 that is, each volume of gas would at a temperature of 4000° be increased 8·2 in volume. Gunpowder when at the temperature of the air being expanded 250 times in volume; therefore 250 by 8·2 = 2,050 as the increased expansion for each volume of gas generated by the explosion of gunpowder at the temperature of 4,000° Fahrenheit. Lieut-Colonel Boxer calculates that the heat generated by good dry powder is not under 3,000° Fahrenheit. Absolute force of gunpowder cannot be determined.It appears with our present knowledge, the absolute value of the force of gunpowder cannot be determined. Still by careful and extensive experiments no doubt a near approximation to the truth may ultimately be arrived at, so that although much has already been done by various eminent philosophers, there is still more to be accomplished; and the importance of the subject ought to act as a stimulus to the exertions of those belonging to a profession the most interested in the question.
Loss of velocity by windage.
It has been found by experiments that in calculating the initial velocity of a projectile, one third of the whole force was lost with a windage of 1⁄10th inch with a shot of 1·96-in. and 1·86-in. in diameter. The bore of the gun being 2·02-in.
Definition of ignition and combustion.
By ignition we understand the act of setting fire to a single grain, or to a charge of gunpowder, and by combustion we mean the entire consumption of a grain or of a charge.
Quickness of combustion.