Wood County reporter. [volume] (Grand Rapids [i.e. Wisconsin Rapids], Wis.) 1857-1923, 1891-01-01
Why the Air Must Be Entirely Re-
moved From the Incandes-
cent Clio be.
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
arc on the series system. The Pittsburg
Dispatch says:
An lncandescent 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 d proper current of electricity
Is sent through the conductor it will in
stantly be brought to a white heat, and
this produces light. This conductor is
usually made of carbonized bamboo or
carbonized silk. The principal details in
the manufacture of this lamp are as fol-
lows: First the glass globe is blown,
leaving 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. A 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
first be prepared in the following manner,
whatever its material may be. A great
many short, silk threads are so wound or
adjusted on block of carbon, that each
thread will have the shape or curve of a
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 burned 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 a
red heat by passing a current of electricity
through them. This operation causes a
deposit of carbon to be made from the oil
flaments. When removed they are found
to be much less brittle than when they
came from the furnace. The next opera
ton is to attach short strip of platinum
wire, about an inch long, to each end of
the horseshoe-shapedc carbon filament.
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 filament, 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
duIl CuI1cup GICll SuIHCu Oil W
a red heat. This heat in the joint causes
carbon (soot) to be deposited there, thus
securing good electrical contact between
the carbon flament and platinum.
The filament is now ready to be inserted
into the glass globe. The loop of course,
goas in first, and after it is in the bottom
of the globe is heated and melted around
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 flament and bring it
to 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
the small glass tube on the top of the bulb
is con nected to mercury pump. and the
lair thus exhausted as far as possible. At
ter this the glass tube is melted and the
bulb sealed, leaving a little point of glass
on the top. A suitable socket is then pro-
vided and switch attached for turning the
current off and now the lamp is ready for
use.
The reason for using platinum wire to
conduct he current through the glass bot
tom to the carbon fiament is this: Glass
vii! OF course expand and contract accord
inh to the temperature to which 1t Is ex-
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 leak will be
formed and air will enter the exhausted
globe. Now to use a technical expression,
platinum has the che same ''coetficlent ex-
pansion'' as glass. This means that for a
given increase in temperature platinum
and glass will expand an equal amount.
This is the only metal known that has the
same ''coefficient of expansion" of glass,
and although it is expensive, yet without
incandescent lamps could not be made.
The object of the vacuum In the g lobe
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 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 unitfs with
the oxygen of the air to form carbonlc-
acid gas, so that when wood is burned in
to the condition of carbonlc-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 is heated to
a white heat the union of these two ele-
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 iucandescent lamp no
combustion can take place; that is, there
will be no oxygen there to combine with
the carbon flament when it is brought to
white heat through the action of the
electric current.
There now remains to be exhibited how
the electric current causes the carbon fila
ment to become white hot. This action IS
simply transformation of energy. live
rub our hands together we transform some
of the energy of the body into heat, frlc
ton being the cause of the transformation.
The condition of the body is one form OF
energy and heat is another form OF energy.
We can SO rub two sticks Of wood togeth-
er that the energy of motion can be trans
formed into the energy of heat to such an
extent as to cause the wood to ignite. Ii we
force water rapidly through a small pipe
the water can be made to boil. The heat
of the water in this case is due to the fric-
ton between the rushing water and the
sides of the pipe.
From business standpointit is neces-
sary to know how many incandescent lamps
can be worked with one horsepower OF
energy. Now, heat and electricity being
forms OF energy from one of which the
other can be obtained, the above 1nforma-
ton is calculated in the following manner !;
The unit of elect RIGA energy Is the ..Watt "