The weekly herald. [volume] (Cleveland, Tenn.) 1876-1888, 1880-02-12
EdI,or,s Lat.st Ele,trie Lirht.

1t is somewhat strange that carbon,
the only substance OF any value for the
contact surface Of telephone transmit
tiers, should also prove to be the only
substance suited to the light giving
portion Of electric lamps. The produc.
ton of an electric light by the incan.
descence of platinum is, for the present
at least, laid aside by Mr.. Y lison for
the o promising and more satisfsc.
tory carbon. Not the carbon so fam
iliarly known in connection withe ~lectrie
lighting, but a new article having
different qualities, and remarkable both
for the simplicity OF the process by
which it is made, snd its eff ciency as a
light-giying body when raised to mean
descence by the passage Of an electrical
current.
The discovery OF this new form OF
carbon was partly accidental, but more
the result OF Mr.. Edison's faculty OF
%6eizipg on the slightest suggestion and
following it as long as it invites investi-
CATION
The first carbon prepared by Mr..
Edison for this purpose was formed Of
a thread enveloped in a paste made Of
lampblack and tar, and ~carbonized by a
high temperature. This carbon thread,
although not remarkably successful,
gave sufficient encouragement to war
rant further investigation in the same
direction. After the trial OF a number
OF other substances it was determined
that the best Of all was paper, simple
plain paper, without lampblack or other
applications. In making these carbons
the quality of cardboard or paper known
as Bristol board is used.
The manufacture OF these little car
bon 'horaeshoes,' as they are called at
Mr.. E1ison's laboratory, is very simple.
The paper blanks, after being cut by
diesin the form Of a horseshoe, about
the size OF the periphery of a silver
dollar, are subjected 70 heat suf1 3iently
strong to drive off by destructive distil-
lation all volatile matter. The paper
horseshoes thus prepared are placed
with alternate layers Of tissue paper in
shallow iron boxes, and weighted down
with tin plates of ordinary carbon.
These boxes are closed by tight. fitting
covers and placed in a muf1e, when
they are raised to q high temperature,
which is maintained for q considerable
time, until the horseshoes are reduced
to the size Of a common thread. The
only index Of the completion of the
process is the cracking of the oxide
formed on the exterior of the iron boxes.
After cooling the carbons are renewed
from the iron boxes and placed between
the jaws of small platinum vises, which
are supported on thin platinum wires
blown in the glass base and forming the
electrodes. A portion of the glass base
and the carbon and its supports are
inclosed in a glass bulb, from which the
air is so completely exhausted by means
Of a Sprengel pump that only a millionth
part Of the original volume remains.
MI. Edison has improved the Sprengel
pump so that high vacua may be pro-
duced in twenty-five minutes instead of
the forty Eve hours consumed in the
operation by some Of our physicists.
The vacuum is so nearly perfect that
none of the tests to which the lamps
have been subjected so far, indicate the
presence of the slightest trace of air.
The electrical resistance OF the slender
carbon horseshoe is 100 ohms, and,
while the lamp is intended to afford
light equivalent to a single four-foot gas
jet, it may be forced to give q light
equal to that of eight or ten such jets.
We saw q single lamp of this kind that
enabled us to read the american 100
feet away. This was certainly an extra
ordinary piece of carbon having a SUI
face no larger than that Of a thread.
The carbon is very tough and flexible.
and not liable to be broken or injured
by jars. We saw one of the carbon
horseshoes nearly Strengthened before it
broke. The carbon not only wristbands
rough mechanical usage; it is also proof
against injury by the sud len turning on
and off Of the electric current. One of
hese carbons has been subjected to the
severe test of applying and removing
the electric current a number of times
equivalent to tEirSy.six years Of actual
daily use, and yet the carbon is not the
least impaired.
The horseshoe firm OF the carbon has
a great advantage over the straight
pencil or the voltaic arc, the light being
more difused, and therefore softer aud
mellower, casting no sharp black shad-
ows, nor giving such an intense light as
to be painful to the eyes. The light
resembles that of q gas jet excepting in
the matter of steadiness, the electric
ightbeing perfectly uniform and steady.
The lamps are connected in multiple
arc, 4. c., tho two wires leading from
the electrical generator run parallel to
each other, and the lamps are placed
between and connected with each wire.
As Mr., Edison has his arranged it does
not make the slightest difference, so far