« EdellinenJatka »
call the natural pressure, a static pressure corresponding, to take a familiar case, somewhat with the barometric pressure of the atmosphere; the other quantity depends on the rate of evolution of the powder gas, and corresponds almost exactly with the pressure on a surface due to a wind. Suppose a very low barometric pressure forward of a shell, a high barometric pressure in rear with a strong wind blowing directly into the chamber of the gun, and the case is not dissimilar to what really must take place when a progressive powder is burnt in a gun. When the powder is all burnt, to carry on the similarity, the wind will almost instantly die out and the gas will exert a pressure due to its weight, volume and temperature alone, a purely static pressure.
The quantity depending on the rate of evolution of the powder gas plays a still more important part with explosive compounds than with powder. If a finite quantity of explosive could be burned and equalized (as regards temperature and pressure) in an infinitesmal time, the pressure would be infinite. This is not realized, but is approached, when explosives are detonated. It undoubtedly partly, if not entirely, accounts for the great differences observed between the results of primary and secondary explosions of the same explosives.
It must be remembered that there are a number of different ways in which the subject of powder in guns may be treated, and in choosing any particular way the reasons that lead to that choice should be given. No theory or practice can make a progressive powder do more work than an instantaneous powder, though experiment seems to show that the former may do more of useful work. The theory chosen makes them equal as to work, and the experimental method of determining coefficients (by means of velocities in two guns) assumes them equal as regards useful work. In this latter the method is slightly in error. A factor of effect may be involved in the above-mentioned coefficients (A and B of formula (15) or M and TV of (20), "Velocities and Pressures in Guns"). If this factor is found to vary slightly with the size of guns, the coefficients for any powder for a certain gun should be determined from guns of approximately the same size. For fairly approximate values of the coefficients to cover a number of guns of different sizes, guns of nearly the extreme sizes should be chosen. Dissimilar guns or dissimilar loadings should always be chosen, in order to make the ratios of the two terms of the formula as different as possible for the different guns, thus permitting a more accurate solution where the given quantities are at best only approximate.
Many powders now-a-days are not uniformly dense, being most dense on the surface and correspondingly slow burning, and least dense in the interior. If the velocity of combustion of powder varied inversely as the density, the formulas for velocity and pressure as deduced would apply equally well to these powders, provided that layers of uniform density were regularly arranged in the powder grains. This law, however, does not hold, and this fact may be expected to cause some error in the use of the formulas of "Velocities and Pressures in Guns."
It may be remarked that with slow-burning powders, such as is German cocoa powder when used in the 6-inch B. L. R., there is an interior layer in the grain that might as well be non-explosive, so far as giving velocity to the projectile is concerned.
A part of the work done by powder is done on the gun itself. In fact, the gun is only a projectile of certain mass (or virtual mass), and a pressure and velocity curve could readily be constructed for the travel of the gun while the projectile is in the gun, just as for the travel of the projectile during the same time. The work done on the gun in this way is of course small relatively, and taking account of it would generally be a useless refinement.
It may be stated, in closing, that no method dealing with pressures in guns as purely static can account for the velocities obtained. The pressures are partly static. The resistance to the projectile in air is quite similar to the pressure in the gun, and, as well as the resistance to a ship moving through the water, is very largely dynamic. The greater the velocity with which the explosive gas is evolved, the greater the pressure; just as in the air, the greater the velocity of the projectile (or the more quickly the air ahead is compressed and that in rear expanded), the greater is the resistance.
U. S. NAVAL INSTITUTE, NEWPORT BRANCH,
NOTES ON THE LITERATURE OF EXPLOSIVES.* By Charles E. Munroe.
United States Letters Patent No. 409943, August 27, 1889, have been granted Stephen H. Emmens for " Gun and Projectile for High Explosives," in which he claims to have invented " a new and useful improvement in apparatus for utilizing high explosives in warfare, (No. 2)." This invention is additional to his improvement in apparatus for utilizing high explosives in warfare.f set forth in his application for U. S. Letters Patent, filed January 27, 1888, serial No. 262172.
The present apparatus is especially designed and adapted for use by infantry and in small boats; and the invention consists in a novel combination of parts, whereby he claims to be enabled to lighten the apparatus to any required extent, and to support a relatively short powder-tube for the propelling charge within the guide bore of the torpedo by means of a tube in line therewith, that incloses the firing device, and is in turn supported by a simple stock in the form of a stake or the like. A drawing accompanies his specification representing an elevation of a torpedo-gun and a bird-torpedo, illustrating the invention.
The " firing mechanism," as he terms it, especially distinguishing the present weapon, comprises a wooden stock fitting into and supporting a metallic tube, and axially perforated and slotted at its front end to accommodate within said tube a rod, which is bent at right angles at its rear end to form a trigger that projects outward through a bayonet-joint slot in the stock and tube. The front end of this rod is fixed in a piston which carries a firing-pin, and between said piston and the front end of the stock is a spiral spring; hence when the trigger is pulled back and turned into the holding-notch of the bayonet-joint slot, said spring is compressed, and when the trigger is released the spring urges forward the piston, with its firing-pin, to explode the propelling charge. This is contained within a short "gun-cartridge shell " or powder-tube, which fits into the front end of said tube and is coupled thereto by a pair of bayonet-joints. Preferably the "powder-tube," as it is termed, is provided with a primer-recess in its breech end, and with an axial ignition tube extending forward from said primer-recess to the front of the propelling charge, which may be of any suitable explosive. The ignitiontube is filled with gunpowder, and the recess is provided with a suitable percussion primer. When the latter is exploded by the firing-pin a sheet of flame is produced within the tube, which ignites the propelling charge at its front end, so as to insure its perfect combustion and an effective discharge of the weapon.
•As it is proposed to continue these Notes from time to time, authors, publishers, and manufacturers will do the writer a favor by sending him copies of their papers, publications, or trade circulars. Address Torpedo Station, Newport, R. I.
tProc Nav. Inst. 15, 289; 1889.
The bird-torpedo comprises a tube fitting closely over the metallic tube and powder tube above mentioned, and plugged at its forward end by the screw-stem of a conoidal torpedo-head. In an external annular charge-space immediately behind the head and around said tube, cartridges of emmensite, or other high explosive, are arranged side by side to form the high explosive charge. By using cartridges of different lengths the size of the charge may be varied to any required extent. These cartridges are held in position by a collar and a cylindrical jacket, and they are fired by a time-fuze. The rear end of the torpedo-tube is provided with three equidistant wings. An annular screen is fitted to the metallic tube of the torpedo-gun immediately in front of the trigger to protect the hand of the person discharging the weapon from any escape of heated gases.
The drawing shows the weapon planted in the ground for firing, but any other mode of mounting may be employed, e. g. the stock may be clamped in a holding-tube on an ordinary swivel stand or gunwale attachment.
In conclusion he claims as his invention: In combination with a thimble-shaped projectile having an axial guide tube open at its rear end and surrounded by an annular charge-space for high explosives, a short powder tube and a tube inclosing a firing device, coupled together end to end and fitted to the interior of said guide tube, and a stock fitted at its front end to the rear end of said firing device tube, substantially as described.
The Ann. des Mines 5, 197-376; 1888, contains a very valuable "Report of the French Commission for Explosive Substances on the Use of Explosives in Presence of Fire-damp," in which the authors state that having satisfied themselves, both from the results of previous investigations and in some preliminary experiments, that mixtures of coal-dust and air were not as dangerous as mixtures of marsh-gas and air, they have restricted themselves to the latter and more dangerous mixture. The experiments were conducted in a boiler which, by suitable arrangement, could be completely filled with a gaseous mixture of known composition, and the explosive under examination was suspended in the middle of the boiler and fired by the aid of electricity, the effect on the gaseous mixture being ascertained by the alteration in pressure observed on a pressuregauge.
The marsh gas was prepared from sodium acetate and soda-lime and stored in a gasometer; it contained per cent 10.8 of air, 7.9 absorbed by bromine, no carbonic anhydride, and 81.3 of methane (by difference). The mixture introduced into the boiler contained generally about 10.3 per cent of methane; this approximates to the most explosive mixture, whilst a 6 per cent mixture verges on the limits of non-inflammability.
The first series of experiments were tried with unconfined explosives freely suspended in the gaseous mixture, this being the most dangerous condition; such experiments are useful to ascertain the actual safety of an explosive.
The explosives investigated were: Ordinary powder; dynamite containing 75 per cent of nitroglycerol and 25 per cent of silica; Paulilles ammoniacal dynamite, a mixture of varying proportions of nitroglycerol, ammonium nitrate, and of a carbonaceous substance destined to utilize the excess of oxygen produced by the detonation of the nitroglycerol and ammonium nitrate; gun-cottons of the general formula Cj(H10_»N.O.0+ ,., in which the maximum value of n should be 12, but which in practice does not exceed II. The following table represents the number of cubic centimetres of nitric