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Page 13
In both tables dynamite No. 1 is assumed as the standard of
comparison. Col. Bucknill states that his gun-cotton results differ
from Gen. Abbot's, because he experimented with much larger
quantities, viz., 500-pound charges. Gen. Abbot's experiments led him
to believe that an instantaneous mean pressure of 6,500 pounds per
square inch would give a fatal blow to the double bottom of a modern
armorclad, and he developed a formula which gives this blow with
blasting gelatine at the following distances under water, viz.:
Pounds.
At 5 feet.................................. 4
" 10 " .................................. 17
" 20 " .................................. 67
" 30 " .................................. 160
" 40 " .................................. 311
Col. Bucknill's experiments caused him to believe that a pressure of
12,000 pounds per square inch is required, and his formula, which is
somewhat different from Abbot's, gives widely different results at
close quarters, but they approach each other as the distance
increases.
His results are as follows:
Pounds.
At 5 feet................................ 231/2
" 10 " ................................ 75
" 20 " ................................ 177
" 30 " ................................ 274
" 40 " ................................ 369
Regarding the comparative effects of gunpowder and the high
explosives, I think Gen. Abbot's estimate of a varying value for
powder is more admissible than the fixed value assigned by Col.
Bucknill. Gunpowder gives a push and detonating compounds a shock; as
the quantities increase, the push reaches farther than the shock.
According to Gen. Abbot, 100 pounds of dynamite No. 1 will have a
destructive horizontal range of 16.3 feet, while the same amount of
gunpowder will only have a range of 3.3 feet. Five hundred pounds of
dynamite, however, will have a horizontal range of 35 feet, and 500
pounds of gunpowder will have 19.5 feet; the ratio has diminished from
five to two. Whether 6,500 pounds or 12,000 pounds per square inch is
necessary to crush the bottom of an armorclad will depend largely upon
how far apart the frames of the ship are spaced and what other bracing
is supplied, as well as many local circumstances. It is difficult to
judge exactly of these matters. Some four years ago the Italian
government adopted treble bottoms for their heaviest ships as a result
of experiments with seventy-five pounds of gun-cotton (the charge of
an ordinary Whitehead locomotive torpedo) against a caisson which was
a _fac-simile_ of a portion of the proposed ships. Only two of the
bottoms were broken through, and when the space between the two inner
bottoms was filled with coal, only the outer bottom was broken.
According to the formul� of either Abbot or Bucknill, there should
have been a local pressure of at least 300,000 pounds per square inch
on the outer skin, and yet judicious interior arrangements rendered it
harmless to the target. It would not, however, be safe to conclude
that the torpedo was thus vanquished; the immediate result was simply
to create a demand for larger locomotive torpedoes for local
application, and but little light was thrown upon the results which
might be anticipated from a large mine at a greater distance, whose
radius of explosive effect would embrace a larger portion of the ship,
and especially if the ship were nearly over the torpedo. The local
effect of a detonation is different from the transmitted shock.
Experiments in England have shown that 500 pounds of gun-cotton at
forty feet below any ship will sink her, and at a horizontal distance
of 100 feet, damage to the interior pipes and machinery is to be
expected.
The fact that the high explosives are so much heavier than gunpowder
has an important bearing on the size of the containing case. Their sp.
gr. is as follows:
Nitro-glycerine............................ 1.6
Blasting gelatine.......................... 1.45
Forcite " .......................... 1.51
Dynamite No. 1............................. 1.6
Wet gun-cotton............................. 1.32
Dry " ............................. 1.06
Gunpowder.................................. 0.9
Their relative efficiency under water per cubic foot, according to
Bucknill, is as follows:
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