Cannon Primer Devices
When the powder bag came into use, the gunner had to
prick 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.
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 scrap 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 potassium 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!
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.
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