The record-union., 1898-09-25
RIFLED MORTARS.
Large Numbers of Terrible En-
gine of Destruction Ordered.

For coast defense the 12-inch NOR
tars are favored pieces of ordnance.
and a large number of these. with re-
turn mortar carriages, have been or
dered by the United States Govern
ment from the Builders Iron Foundry.
Providence, r. l. They are to be dis
tributed along the seaboard in groups
of sixteen, are to be shielded from
the enemy's fire by high earth en-
banlxments and the mortars fired stimuli
taneously by means of electricity.
The Pinch mortars are made from
charcoal pig castings, the mixture of
metal suitable for the purpose being
determined by test trials. The castings
are made breech down, with a straight
cylindrical bore, the exterior, inclusive
of the surplus metal at the bottom, be-
ing cylindrical, With q diameter not
less than thirty-three and one-half
inches. According to the speCifica-
tfons. the metal must flow into the
mold continuously and uniformly, and
any evolution of gas from the mold
or core through the metal may be suffi-
cient cause for rejecting the casting
As soon as the melted metal is found
to be in proper condition for casting
the furnaces are tapped simultaneous
ly and the metal is conducted by
troughs connecting with the side gates
of the mold, and, passing down, enters
the mold cavity by the branches These
branches connect with the side gates
at regular intervals, and are so con-
structed that the metal enters in q
horizontal direction toward the axis of
the mold cavity.
The surface of the metal as it enters
is stirred to prevent the "scoria" from
lodging, care being taken to prevent
a swirl, which throws the lghtest
metal around the core, where the
heaviest should be. When the mold
is filled the tap holes of the furnaces
are closed, and the surface of the metal
in the shrinking head is covered with
a layer of charcoal TO prevent its chill
ing.
The casting is cooled from the in
terror by a current of water, care be-
ing taken that no steam is generated
The metal is then tested. and it's tensile
strength must average at each end at
| least 10000 pounds to the square inch.
When a casting has become cooled
| it is hoisted out from the pit. The
molding composition adhering to the
| interior or exterior is then removed by
| is placed in a lathe, where the surplus
metal is turned off and the interior is
| bored and finished. The mortars are
/ all rifled and finished with breech
! mechanism, and are mounted on car
| riages similar to cannon carriages, eX-
cept that the recoil takes place 30 de-
/ grees from, instead of in. the horizontal
1 plane.
| In these mortars about eighty pounds
! of powder will produce an initial
pressure of some $4,000 pounds to the
] square inch, and give a muzZle velocity
| of 1900 feet a second to a shell of $50
! pounds. This will insure a range of
| about six miles at 40 degrees eleva-
| ton. The shell or hollow steel shot
| contains about thirty pounds of fine
! powder. It's front is turned to a curve
/ called the "ogival," and it's back con-
/ tans a soft metal collar which, when
| forced into the ritiing grooves, gives it
/ the required rotary motion. The primer
| is also placed at the back end of the
shell. It does not move from it's place
when the shot is fired, but is pro-
| jected forward against a Illuminating
cap when an object is struck. - New
| York Tribune.