Part 2 (2/2)
Making corned powder was fairly simple. The three ingredients were pulverized and mixed, then compressed into cakes which were cut into ”corns” or grains. Rolling the grains in a barrel polished off the corners; removing the dust essentially completed the manufacture. It has always been difficult, however, to make powder twice alike and keep it in condition, two factors which helped greatly to make gunnery an ”art” in the old days. Powder residue in the gun was especially troublesome, and a disk-like tool (fig. 44) was designed to sc.r.a.pe the bore. Artillerymen at Castillo de San Marcos complained that the ”heavy” powder from Mexico was especially bad, for after a gun was fired a few times, the bore was so fouled that cannonb.a.l.l.s would no longer fit. The gunners called loudly for better grade powder from Spain itself.
How much powder to use in a gun has been a moot question through the centuries. According to the Spaniard Collado in 1592, the proper yardstick was the amount of metal in the gun. A legitimate culverin, for instance, was ”rich” enough in metal to take as much powder as the ball weighed. Thus, a 30-pounder culverin would get 30 pounds of powder. Since a 60-pounder battering cannon, however, had in proportion a third less metal than the culverin, the charge must also be reduced by a third--to 40 pounds!
[Ill.u.s.tration: Figure 16--GUNPOWDER. Black powder (above) is a mechanical mixture; modern propellants are chemical compounds.]
Other factors had to be taken into account, such as whether the powder was coa.r.s.e-or fine-grained; and a short gun got less powder than a long one. The bore length of a legitimate culverin, said Collado, was 30 calibers (30 times the bore diameter), so its powder charge was the same as the weight of the ball. If the gunner came across a culverin only 24 calibers long, he must load this piece with only 24/30 of the ball's weight. Collado's _pasavolante_ had a tremendous length of some 40 calibers and fired a 6- or 7-pound lead ball. Because it had plenty of metal ”to resist, and the length to burn” the powder, it was charged with the full weight of the ball in fine powder, or three-fourths as much with cannon powder. The lightest charge seems to have been for the pedrero, which fired a stone ball. Its charge was a third of the stone's weight.
In later years, powder charges lessened for all guns. English velocity tables of the 1750's show that a 9-pounder charged with 2-1/4 pounds of powder might produce its ball at a rate of 1,052 feet per second.
By almost tripling the charge, the velocity would increase about half.
But the increase did not mean the shot hit the target 50 percent harder, for the higher the velocity, the greater was the air resistance; or as Muller phrased it: ”a great quant.i.ty of Powder does not always produce a greater effect.” Thus, from two-thirds the ball's weight, standard charges dropped to one-third or even a quarter; and by the 1800's they became even smaller. The United States manual of 1861 specified 6 to 8 pounds for a 24-pounder siege gun, depending on the range; a Columbiad firing 172-pound shot used only 20 pounds of powder. At Fort Sumter, Gillmore's rifles firing 80-pound sh.e.l.ls used 10 pounds of powder. The rotating band on the rifle sh.e.l.l, of course, stopped the gases that had slipped by the loose-fitting cannonball.
Black powder was, and is, both dangerous and unstable. Not only is it sensitive to flame or spark, but it absorbs moisture from the air. In other words, it was no easy matter to ”keep your powder dry.” During the middle 1700's, Spaniards on a Florida river outpost kept powder in gla.s.s bottles; earlier soldiers, fleeing into the humid forest before Sir Francis Drake, carried powder in _peruleras_--stoppered, narrow-necked pitchers.
As for magazines, a dry magazine was just about as important as a sh.e.l.l-proof one. Charcoal and chloride of lime, hung in containers near the ceiling, were early used as dehydrators, and in the eighteenth century standard English practice was to build the floor 2 feet off the ground and lay stone chips or ”dry sea coals” under the flooring. Side walls had air holes for ventilation, but screened to prevent the enemy from letting in some small animal with fire tied to his tail. Powder casks were laid on their sides and periodically rolled to a different position; ”otherwise,” explains a contemporary expert, ”the salt petre, being the heaviest ingredient, will descend into the lower part of the barrel, and the powder above will lose much of its goodness.”
[Ill.u.s.tration: Figure 17--SPANISH POWDER BUCKET (c. 1750).]
In the dawn of artillery, loose powder was brought to the gun in a covered bucket, usually made of leather. The loader scooped up the proper amount with a ladle (fig. 44), and inserted it into the gun. He could, by using his experienced judgment, put in just enough powder to give him the range he wanted, much as our modern artillerymen sometimes use only a portion of their charge. After Gustavus Adolphus in the 1630's, however, powder bags came into wide use, although English gunners long preferred to ladle their powder. The powder bucket or ”pa.s.sing box” of course remained on the scene. It was usually large enough to hold a pair of cartridge bags.
The root of the word cartridge seems to be ”carta,” meaning paper. But paper was only one of many materials such as canvas, linen, parchment, flannel, the ”woolen stuff” of the 1860's, and even wood. Until the advent of the silk cartridge, nothing was entirely satisfactory. The materials did not burn completely, and after several rounds it was mandatory to withdraw the unburnt bag ends with a wormer (fig. 44), else they acc.u.mulated to the point where they blocked the vent or ”touch hole” by which the piece was fired. Parchment bags shriveled up and stuck in the vent, purpling many a good gunner's face.
PRIMERS
When the powder bag came into use, the gunner had to p.r.i.c.k the bag open so the priming fire from the vent could reach the charge. The operation was accomplished simply enough by plunging the gunner's pick into the vent far enough to pierce the bag. Then the vent was primed with loose powder from the gunner's flask. The vent prime, which was not much improved until the nineteenth century, was a trick learned from the fourteenth century Venetians. There were numerous tries for improvement, such as the powder-filled tin tube of the 1700's, the point of which pierced the powder bag. But for all of them, the slow match had to be used to start the fire train.
[Ill.u.s.tration: Figure 18--LINSTOCKS.]
Before 1800, the slow match was in universal use for setting off the charge. The match was usually a 3-strand cotton rope, soaked in a solution of saltpeter and otherwise chemically treated with lead acetate and lye to burn very slowly--about 4 or 5 inches an hour. It was attached to a linstock (fig. 18), a forked stick long enough to keep the cannoneer out of the way of the recoil.
Chemistry advances, like the isolation of mercury fulminate in 1800, led to the invention of the percussion cap and other primers. On many a battleground you may have picked up a sc.r.a.p of twisted wire--the loop of a friction primer. The device was a copper tube (fig. 19) filled with powder. The tube went into the vent of the cannon and buried its tip in the powder charge. Near the top of this tube was soldered a ”spur”--a short tube containing a friction composition (antimony sulphide and pota.s.sium chlorate). Lying in the composition was the roughened end of a wire ”slider.” The other end of the slider was twisted into a loop for hooking to the gunner's lanyard. It was like striking a match: a smart pull on the lanyard, and the rough slider ignited the composition. Then the powder in the long tube began to burn and fired the charge in the cannon. Needless to say, it happened faster than we can tell it!
[Ill.u.s.tration: Figure 19--FRICTION PRIMER.]
The percussion primer was even more simple: a ”quill tube,” filled with fine powder, fitted into the vent. A fulminate cap was glued to the top of the tube. A pull of the lanyard caused the hammer of the cannon to strike the cap (just like a little boy's cap pistol) and start the train of explosions.
Because the early methods of priming left the vent open when the cannon fired, the little hole tended to enlarge. Many cannon during the 1800's were made with two vents, side by side. When the first one wore out, it was plugged, and the second vent opened. Then, to stop this ”erosion,” the obturating (sealing) primer came into use. It was like the common friction primer, but screwed into and sealed the vent.
Early electric primers, by the way, were no great departure from the friction primer; the wires fired a bit of guncotton, which in turn ignited the powder in the primer tube.
MODERN USE OF BLACK POWDER
Aside from gradual improvement in the formula, no great change in powder making came until 1860, when Gen. Thomas J. Rodman of the U. S.
Ordnance Department began to tailor the powder to the caliber of the gun. The action of ordinary cannon powder was too sudden. The whole charge was consumed before the projectile had fairly started on its way, and the strain on the gun was terrific. Rodman compressed powder into disks that fitted the bore of the gun. The disks were an inch or two thick, and pierced with holes. With this arrangement, a minimum of powder surface was exposed at the beginning of combustion, but as the fire ate the holes larger (compare fig. 20f), the burning area actually increased, producing a greater volume of gas as the projectile moved forward. Rodman thus laid the foundation for the ”progressive burning” pellets of modern powders (fig. 20).
[Ill.u.s.tration: Figure 20--MODERN GANNON POWDER. A powder grain has the characteristics of an explosive only when it is confined. Modern _propellants_ are low explosives (that is, relatively slow burning), but _projectiles_ may be loaded with high explosive, a--Flake, b--Strip, c--Pellet, d--Single perforation, e--Standard, 7-perforation, f--Burning grain of 7-perforation type. Ideally, the powder grain should burn progressively, with continuously increasing surface, the grain being completely consumed by the time the projectile leaves the bore, g--Walsh grain.]
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