Mineral Point tribune. (Mineral Point, Wis.) 1869-1938, 1891-01-03
Why the Air Must Be Entirely Re-
moved From the lncandeS'
cent Globe,
Construction of the Globe and How
the Filament is Attached to
the Wire.
How the Electric Current Causes the
Slender Carbon Filament TO
Become White Hot

descent are commonly used on the parallel
system of electric distribution and the
are on the series system The Pittsburg
Dispatch says;
An incandesceut lamp consists of glass
globe, in size and shape very much like a
pear; and an electric conductor inside this
globe, of such construction and material
that when proper current of electricity
is sent through the conductor it will in
stantly be brought to IL white heat and
this produces light This conductor is
usually made of carbonized bamboo or
carbonized silk The principal details in
the manufacture of Tins lamp are as fol-
lows: First the glass globe is blown,
leaving a hole at the bottom or smaller
end of the globe large enough to admit
the Illuminating conductor above men
ioned. This conductor is called the fla
ment small hole is also left in the top
of the globe and provided with glass
tube through which the air in the bulb is
eventually pumped out
The bulb in this condition is ready to
receive the filament, which, however must
first be prepared in the following manner,
the preparation being very much the same,
whatever its material may be- A great
many short, silk threads are so wound or
adjusted on a block of carbon, that each
thread will have the shape or curve Of
horseshoe--in fact, the very same shape
that can be seen in any incandescent
lamp In use. The carbon block with the
silk threads have been BURIED into car
bon.
When removed from the furnace they
are hard and brittle. In this condition
they are immersed in gasoline oil and
while under the oil they are brought to IA
red heat by passing a current of electricity
through them, This operation causes a
deposit of carbon to be made from the oil
ilaments When removed they are found
to be much less brittle than when they
came from the furnace. The next opera
ton is to attach a short strip Of platinum
wire, about an inch long, to each end Of
the horseshoe-shaped carbon flament
The method of making this Joint Is very
interesting and is as follows First the
platinum wire is twisted or camped
around the end Of the hlament, then one
pole of an electric circuit is connected to
one side Of the Joint and the other pole to
the other side of the Joint In this con-
diuon the Joint is immersed IN gasoline oil
and sufficient current then turned on to
a red Feat This heat in the joint causes
carbon (soot) to be deposited there, thus
securing good electrical contact between
the carbon flament and platinum
The flament is now ready to be inserted
into the glass globe. The loop, of course,
goes in first, and after it is in the bottom
of the globe IS heated and melted Ground
the two platinum ends and thus hermetic-
ally sealed at that point. The two ends of
the platinum wires are left protruding
through the glass bottom, and to these are
attached two copper wires, which are
eventually to be attached to the two poles
of an electric circuit, so that the current
may flow through the hlament and BRING it
to a white heat for lighting purposes.
The only thing left to be done now is to
pump the air out of the bulb and then the
lamp will be ready for use. To do this
the small glass tube on the top of the bulb
is con nected to a mercury pump, and the
! iair thus exhausted as far as possible. At
ter this the glass tube is melted and the
| bulb sealed, leaving little point of glass
on the top. A suitable socket is then pro-
vided and a switch attached for turning the
current off and now the lamp is ready for
use.
The reason for using platinum wire to
conduct the current through the glass bot
| tom to the carbon tilament is this: Glass
will OF course expand and contract accord
! inh to the temperature to which 1T Is eE-
| posed, and the wire leading through the
glass will do the same, but if the glass and
wire expand equally for given increase in
temperature the glass will mos, likely
| crack, and sooner or later a leak will be
formed and air will enter the exhausted
globe. Now to use technical expression,
platinum has the che same 'coetflclent e1-
pansion" as glass. This means that for
given increase in temperature platinum
and glass will expand an equal amonnt.
This is the only metal known that has the
! same "coeiicieut of expansion of glass,
and although it is expensive, yet without
incandescent lamps could not be made.
The object of the vacuum in the globe
Of an incandescent lamp IS to prevent
combustion. When we burn wood or
coal we do not destroy anything that Is
matter, we simply cause a change in the
condition of things. Wood when burned
is not destroyed as far as matter Is con-
cerned; it has simply changed its condi-
ton. The carbon Of the wood unitss with
the oxygen of the air to form carbonlc-
acid gas. so that when wood is burned In
to the condition of carbonic-acid gas and
the rest into ash.
Now carbonic acid gas is composed Of
carbon and oxygen-but if there is no
oxygen present when carbon j. heated TO
! a white heat tn. union Of these two ee
ments cannot take place 1t will now be
perfectly clear that if we pump the air,
which is largely composed OF oxygen out
Of the globe Of an iucHldpsgent lamp no
..ombRstioD can take mace. that is there
will be no oxygen there to combine with
the carbon flament when it is broughrto
a white heat through the action Of the
electric current.
There now remains to be exhibited how
the electric current causes the carbon fla
ment to become white hot. This action Is
simply Transformation Of energy. five
rub our hands together we transform some
Of the energy Of the body into heat fric
tiUn being the cause of the transformation.
The condition Of the body is one form Of
energy and heat j. another form Of energy.
We can so rub two sticks Of wood togeth-