Delaware gazette and state journal. (Wilmington, Del.) 1883-1902, 1889-01-17

The Electric World writes up, with IL.
lustrations, in its last issue, the Cobb
vu'csnite wire manufacturing plant
now in full blast In the buildings
formerly occupied by the Whining
ton branch of the NOR canneries,
on the eastern bank of the Brandywine
below the Pullman car shops. Without
going into technioaIities that only cleo
trioians would fully comprehend, it may
be briefly said that the Electric World re-
CARDS this establishment as big thing
and very important addition to the
rapidly growing electric industries
OF the United States. II re-
cites that, although the qualities of
hard rubber as an insulator have been
long known and tested, the employment
Of such insulation for electric wires has
been heretofore very limited on account
OF the difficulty of manufacturing such
insulated wires OF sufficient continuous
length. This difficulty has been over.
come by the Cobb process, "now EN-.
ployed by the recently established, extern
sive and we'll equipped works at Will
mington." This inhalation consists of
flexible hard rubber, the rubber being
vulcanizsd so that 1t is not burned, but,
though hard, is flexible and capable Of
being bent at an angle. During the
process the insulation is subjected to o
pressure Of rs pounds to the squars
inch, which solidiHes 1t and removes
oil the DIR holes. The wire is then in
serted into theae long lengths of tubing,
by special process, and lies wholly
though snugly in it, touching the insula-
ton at but comparatively few points.
The high insulating properties of the
rubber and the smallness Of contact be.
tween the wire aud rubber, combine to
make the Insulation resistance unusually
high, as shown BY numerous tests. The
ak rubber tubing machines now in use
at the Cobb works have q combined
capacity of over Ave miles of electric
light cable per day and ere kept running
at their fullest capacity. All this has
been said before by the GAZETTE, but
Wilmington readers cannot fail to be In
terested in this resume of o description
taken from Buch authority in this special
field.
Equally interesting but mora technical
is the Electric Worlds description, assisted
by large cut, OF the elaborate testing
apparatus, designed especially fer this
establishment by Carl Herring. It's chief
element is a double-coii nstatio Carpen-
der.Thomson galyanometer Of the most
sensitive type, with 1000 turns of wire
and 16, 100 ohms resistance, the wire
being only onesirteenth of millimeter
(about 1-400th part of an inch) In
diameter. Owing to the extremely high
insulation Of the wire to be tested, IL was
found that very powerful battery wss
required, notwithstanding the galyano-
meter was the most sensitive that could
be obtained. This battery, described in
de.SA y gne article referred 60, was alsa
dssisued expressly By Gail Herring
aud tas TESTIFY apparatus complete vas
designed to measure about so. 900 megohms
though under favorable conditions, it
will measure as high as 100, 900 megohms.
Coming down into more practical Eng
lish we are told that with "a provisional
half-meter bridge wire" dead fault was
located in piece of heavy electric light
cable 1857 feet long. The test uoated |
the fault ct 2s9 feet from one end. By |
cutting the wire it was found that tho ex- |
act location Of the fault was "a feet, z |
inches from the end, showing but little |
more than one foot of error in l 1857 feet
Of wire. The galvanometer DETECTION
showed that il the bridge wire had been
longer, or the fault nearer the middle Of
the cable, still greater accuracy could
have been obtained.