Evening star., 1943-07-19
Du Pont Expert Calls
Explosives the Tool
Of Industry and War
BY DIR. JAMES X. HUNT,

BY DIR. JAMES X. HUNT,
e. I. Du Pont de Nemours g. Co.
WILMINGTON, Del, July 19.-
Recent announcement by Maj. Gen.
L. H. Campbell, jr., chief of Army
ordnance, of new explosive said
to be 35 per cent more powerful
than INT, has stimulated fresh
interest in the why's and where
fores of explosive materials.
Strange as it may seem to those
who think Of explosives largely in
connection with war, materials of
this type are used chiefly for peace
full jobs. Commercial explosives,
such as dynamite, blast out coal,
ores and rock, and speed the con-
struction of dams, tunnels, highways
and harbors. For such jobs, in a
normal year, the United States con-
sumes some 35O,O0OOOO pounds of
dynamite. The total this year may
reach 450,0O0,000 pounds.
In laying the big Inch," the
worlds largest pipeline, to bring
oil from Texas to- the East, ap-
proximately 100000 pounds of dyna-
mite were used
Labor Saving Device.
Dynamite unquestionably ranks
among the great labor saving de-
vices of all time With IS cents
worth of explosives, and another
IS cents worth of drilling, some
four to six tons of rock may be put
into useful form. History records
that 100000 slaves labored 80 years
to build the great pyramid of Giseh.
Grand Coulee Dam, a structure
three times as large, was built in
a fraction of the time and with
fraction of the workers-thanks to
dynamite.
No simple definition would fit
every explosive. All of them, how
ever, are substances which, suitably
stimulated, decompose with vio-
lence. That is. they go off with
bang" But the stimulus required
to set them off varies widely. Some,
like INT, are so insensitive as to
withstand the impact of a high
power rife bullet without exploding
Others, like nitrogen iodide, may
be set of by the gentle touch of a
feather.
Primer and Booster"
For the primer or detonator In
the nose Of high-explosive shell,
a small amount of rather sensitive
nvr1Nciua &c mead 1noI nj Ia
or illuminate of which is
set off by percussion when the shell
strikes something solid. or by
timing mechanism as is employed
in some antiaircraft shells. Next
may come the booster" charge, tri-
ylmethylnitramine ("tet-
ryl') being typical of this class of
explosive.
Boosters are less sensitive than
the primer, but more sensitive than
the high explosive bursting charge.
The booster" makes 1t necessary to
use only small amount of sensitive
and relatively dangerous primer,
and insures complete detonation of
the TINT bursting charge. Frequent
ly q time fuse comes between the
primer and booster" to delay de-
tonation of the main bursting
charge until, for example. the shell
has passed through the armor plate
of a battleship.
Large volumes of gases are set
free when most explosives go off.
Furthermore, the temperature of an
explosion may be 5000 degrees F..
or higher, which greatly expands
the liberated gases. AS a result,
the volume of hot gases formed may
be from 10000 to $1,000 times the
volume of the exploded material
It is the large volume of gas liber-
ated when smokeless powder burns
that "propels" the shell out of a
big gun and sends it on its deadly
mission, possibly Is miles away.
Factors Of Energy.
The energy of an explosive de-
pends on several factors, including
the volume of gases produced and
the amount Of heat given off. 1t
is commonly measured by shoot
ing definite amount of the ex-
plosive in a "ballistic mortar"
device somewhat like heavy
swinging cannon, and observing how
much swing is impaired to the
mortar by the kick" Of the explo-
sion. The greater the swing, the
greater the energy.
Explosives are divided into two
main types, propellents and high
explosives, depending upon the
speed at which they burn on de-
compose. The faster the burning,
the faster energy is released. In
turn, rate of burning depends upon
such factors as particle size, den-
sity, and pressure.
Black powder, first used as a
propellent by the English in 1916
in the Battle of Crecy, burns at a
rate of only fraction of an inch
per second in the open air. Con-
fined, however, so that high pres-
sure is built up, the rate of burn
ing may be ten times as great. The
rate of combustion of smokeless
powder likewise increases with pres
sure, but in no case-in a 16-inch
gun, for example-does the average
rate exceed three or four inches
per second. In contrast, the We
locity of detonation of a high ex-
plosive-dynamite or INT, for ex-
ample-may exceed 10000 feet a
second.
(Released Through North American
Newspaper Alliance)