Cincinnati daily press. [volume] (Cincinnati [Ohio]) 1860-1862, 1861-10-09
THE DAILY PRESS,
Heavy Ordnance-Wh Guns are Cast
HoIlovv

at Fortress Monroe. The writer evinces
much greater degree Of familiarity with the
matter than is apparent in the generality
Of newspaper articles which have appeared
in the East on this subject. lie speaks in
very flattering terms of Captain Rodman,
the discoverer of the principle of "hollow-
casting" guns, and the manufacturers
Knap, Rudd & Co., of this city. But in
speaking Of the defects Of the guns cast
solid, which the principle was intended to
remedy the writer appears to have wholly
misunderstood the effect Of the contraction
of metal upon solid guns He says;
$50 long as pieces ofa small caliber were
the only kind in use, the evils resulting
were not very serious though it was inya-
riably found that in boring these guns the
hardest and most compact material was in
the center, while as the cutters approached
the circumference, the density of the metals
grew appreciably less. Thus when gun
is cast solid, as is usually the case, the
hardest and best metal is bored out, while
the softer and weaker is left to form the
cylinder Of the gun"
1t is clearly apparent from this paragraph
that the writer has not very accurate
knowledge of the process of contraction in
the metals composing the gun, or its effect
is here asserted is really the case, the iron
at the circumference of a solid gun being
extremely dense and hard, while that in the
interior is porous and soft The object aimed
at in hollow-casting is to remove this rela-
tive condition of the metal to some extent.
Without attempting to give any thing like
scientific explanation of the causes which
lead to this condition of the metals, we may
be permitted to demonstrate the absurdity
of the statement made by the writer in the
Post.
Molten metal is assumed in scientific for
mula to contract, in cooling, one-tenth ofan
inch in each lineal foot. The degree Of con-
traction varies under different circum-
stances, with different grades Of metal, but
this proportion is generally assumed in cal
culation The greatest exterior diameter
of a ten-inch gun, when taken from the pit,
is thirty-two and q half inches, or an area
of transverse section of about eight hun
dred and twenty-seven and a half inches.
Supposing, for the purpose Of illustration,
that the outside Immediately cools forming
q shell inclosing the molten mass, which
shell gradually increases in thickness to-
ward the interior, as the cooling progresses.
AS the metal which fills this area must con-
tract one-tenth Of an inch to the foot in
lineal Dimensions, or one-hundredth Of
square inch to the square foot in area, in
cooling, q space of that relative proportion
would be left hollow in the center of the
gun. But the process of cooling does not
follow precisely the course assumed, the
metal at the exterior being still red hot
when the solidifcation reaches the interior.
Still the outside is always in advance, as it
were, of the interior, in cooling, and shrink
ing upon itself. forms a shell upon the gun
almost as dense as steel, while the interior
metal, in contracting, becomes porous and
soft. So hard is the exterior shell that it is
considered to add materially to the strength
Of light, cast-iron field pieces to leave them
unfinished on the exterior.
In boring out one of these solid guns,
which is so dense at the surface, the center
is invariably found to be more or less
spongy. The part cut out in boring is prob
ably affected to the greatest degree by this
sponginess, but the circumference Of the
bore is still of comparatively very soft
metal, cutting away easily on every dis
charge Of the gun, altering in conformation
and dimensions, and finally bursting In
Rodman's plan the gun is cooled by stream
of water running through the barrel, while
the exterior heat is kept up as long as pos
sible. The process of contraction is thus
started at the CENTER dense shell forming
on the core-barrel, and gradually thickening
as the cooling extends outward. There is
an additional advantage, of metal shrinking
nto smaller concentric circles, gained in
this plan, and probably far less strain on
the component particles of the metal ex-
cept in the direction required-toWard the
center.
The work of boring out hollow-cast gun
is infinitely more laborious than that OF
boring solid gun through the mass of
metal is 10 be removed comparatively small
This is owing to the extreme density and
hardness Of the iron, which is almost "chill
hardened, and has stood one thousand
rounds with scarcely perceptible enlarge
ment.
The writer continues with condensation
of the report of the Board of Officers who ex-
perimented with the fifteen-inch gun, rela-
tive to the success of that monster piece of
ordnance. He draws the deduction from
the report notwithstanding the
opinion of John Whitworth that cast-iron
guns beyond certain caliber were useless
guns of the very largest caliber may be
worked in connection with rifed cannon,
for long ranges, with snch formidable effect
that no fleet, however equipped-no floating
fortifcatiop, however protected-would at
tempt to pass an array of batteries so armed.
The writer states that guns even of larger
caliber have been projected, but we have
been unable to learn that any preparations
are making for their manufacture. The
statement that a twenty-inch gun was to be
made at the Fort Pitt Works seems to have
originated in the brain of some individual,
Save struck, like the Philadelphia Press
man, by view of the huge guns not in
manufacture.