IMPROVEMENTS IN STRUCTION AND MANUFACTURE OF ELECTRIC LAMPS
Year: 1881

page_text: LETTERS PATENT to William Crookes, F.R.S., of Boy Court, Ludgate Hill, in
the City of London, for an Invention of "IMPROVEMENTS IN
STRUCTION AND MANUFACTURE OF ELECTRIC LAMPS."
THE CON-
PROVISIONAL SPECIFICATION left by the said William Crookes at the
Office of the Commissioners of Patents on the 31st August 1881.
WILLIAM CROOKES, F.R.S., of Boy Court, Ludgate Hill, in the City of London,
"IMPROVEMENTS IN THE CONSTRUCTION AND MANUFACTURE OF ELECTRIC
LAMPS,"
This Invention relates to that class of electric lamps in which the light is
produced by the heating of a continuous conductor, which is usually composed of
a fine filament of carbon enclosed in a glass globe, and protected from combustion
by being surrounded by a vacuous space or by an atmosphére that will not support
combustion.
To make the lamp I take a cylinder of glass of any convenient size and form,
and after drawing down one end in the blow pipe to make the top of the lamp, I
draw the other end out into a wide neck and seal off its end in the blow. pipe.
While the glass is still soft (or after reheating it), I press the end inwards with a
two pointed brass tool like a two pronged fork, so as to make a hollow projection
stretching a convenient distance into the neck of the tube, and terminating in two
hollow points of glass. When the glass is cool I cut the tube in two across the
neck at such a distance from the end as to leave the two glass points projecting
from the bottom piece of the tube. These points are now opened in the blow
pipe or by breaking off their ends, and the conducting wires are passed through
the openings so made and sealed in the glass by means of white enamel, or what
is technically known as arsenic glass. The top of the cylinder, which was at first
drawn down in the blow pipe, is now finally sealed up and made into a hemi-
spherical end before the blow pipe. The carbon filament can now be attached to
I Price 6d 1

page_text: the conducting wires and the two portions of the tube are then sealed together at
the edges where the tube was cut open.
At some convenient stage of the above process a small glass tube is sealed into
the lamp, perferably at the lower edge, where the glass is bent inwards for the
purpose of exhausting the lamp and filling it with a suitable protective atmosphere.
When the lamp is completed this is sealed off.
The hollow at the base of the lamp may be filled with plaster of Paris or any
other like cement, for the purpose of giving strength to the lamp and protecting
the conducting wires and their attachments. The pores may, if thought desirable,
be filled in with a fusible cement.
If a carbon filament in a lamp breaks, the neck of the lamp can be again cut
across and a fresh filament attached, and the lamp sealed up and exhausted or filled
with gas as before.
I sometimes form the brass tool with only one prong so as to form one hollow
pointed projection into the neck, and then seal in both the conducting wires
close together, but not touching; I also use a brass tool with more than two
prongs if I wish to have two or more filaments together in the same lamp.
One of the chief difficulties in the construction of such lamps is the sealing in of
the wires. It is difficult to make a good junction between the glass and the metal,
except in the case of platinum, and the low conductivity of this metal causes it to
heat when large currents are used, and to crack the glass or cause a leak at the
junction. I get over this difficulty by using a compound wire having a core of
copper, silver, gold, or other conductor, and a platinum sheathing, so that I have
the advantage either of using a cheaper metallic conductor or a metallic conductor
of better conductivity without the difficulty of making it form a good junction
with the glass.
The wire (compound or simple) may be used either cylindrical, or in order still
further to diminish the liability to crack owing to unequal expansion, it may be
flattened out into a ribbon, or curved so that it is of a horse shoe section.
then
For practical purposes it is of the greatest importance that lamps of this class
should all have the same resistance when in use. To accomplish this I proceed as
follows I attach the ends of the carbon filament to two small hollow copper
terminals which are fixed in a small bar of arsenic glass or similar non conductor
so as to keep them at a suitable distance to fit upon the extremities of the
conducting wires. If the carbon filament is sufficiently flexible to stand the
necessary amount of manipulation I dispense with the bar of. arsenic glass;
place the filament in an apparatus consisting of a bell-shaped receiver, which is in
connection with an air-pump and capable of being exhausted by it. The plate
upon which this receiver rests is of ebonite or similar nonconducting substance,
and is fitted with pairs of pointed wires in metallic connection with binding screws
on the outside of the apparatus. The pointed wires in each pair are at the same
distance from each other as the copper terminals of the carbon filaments, so that a
carbon filament can be placed with its terminals in one of the pairs of pointed
wires and a current sent through it from outside while the exhaustion is
going on.
The carbon filaments are placed in this apparatus and the air exhausted, and
their resistance is measured when they are under the same circumstances as in
finished lamps. If any are found to have too high a resistance the current is
maintained through thein, while some hydrocarbon vapour, either pure or combined
with chlorine or analogous element, is admitted into the receiver by putting it into
connection by means of a stop cock with a vessel containing chloroform. This
causes a deposition of carbon on the heated filaments, and so soon as the resistance
of any filament is reduced to the standard amount the current is turned off from
it and the deposition ceases.
I by preference use chloroform vapour on account of the facility of manipulation
and of decomposition, but the vapour of a hydrocarbon or a hydrocarbon gas
can also be used.

page_text: If the resistance of a carbon filament is too low I reduce it by passing the
current through it before the oxygen is wholly removed from the receiver so as to
burn away a portion of the filament.
In order to increase the rigidity of the carbon filaments I make them of a flat
section, and give to them a twist of a quarter of a circle in placing them in the
terminals, so as to make the flat section at the one end of the filament perpendicular
to the flat section at the other. The filament which is fixed in the shape of a horse-
shoe will be found to possess great rigidity.
The improvements last described are chiefly practicable when the carbon is very
elastic and homogenious, as in the case of carbons manufactured by means of the
process described in the Provisional Specification lodged by me on the 15th June
last, No. 2612.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Crookes in the Great Seal Patent Office on the 27th February
1882.
WILLIAM CROOKES, F.R.S., of Boy Court, Ludgate Hill, in the City of London.
"IMPROVEMENTS IN THE CONSTRUCTION AND MANUFACTURE OF ELECTRIC LAMPS."
This Invention relates to that class of electric lamps in which the light is
produced by the heating of a continuous, conductor that is usually composed of a
fine filament of carbon enclosed in a glass globe or vessel, and protected from.
combustion by being surrounded by a vacuous space, or by an atmosphere that
will not support combustion.
In order to form the glass enclosure of the lamp I take a cylinder of glass of any
convenient size, and after drawing down one end in the blow pipe I draw the
other end out into a wide neck and seal off its end in the blow pipe, the neck will
then have been brought approximately to the form shewn at A, Figure 1. While
the glass neck is still hot, or after reheating it, I press the end inwards with a two.
pointed metal tool like a two pronged fork, which may be of the shape shewn in
Figure 2, so as to make a hollow projection B stretching a convenient distance into
the neck of the tube, and terminating in two hollow points of glass; the tube then
has the appearance shown in Figure 3.
At this or some other convenient stage of the process a small glass tube C,
shewn in dotted. lines in Figure 3, is sealed on to the lamp (preferably at the
lower edge where the glass is bent inwards) for the purpose of exhausting the
lamp and filling it with a suitable protective atmosphere if such is desired.
It is desirable that the mouth of the drawn down end of the cylinder should be
previously sealed, as shewn by the dotted line D, so as to facilitate the blowing on
of the tube.

page_text: If this tube be sealed on to the lamp at this stage it will present the appearance
shewn in Figure 3, but it is not necessary that the small tube last described should
have the particular position there shewn. The top of the lamp should now be
sealed off before the blow pipe and formed into a hemispherical end, as shewn by
the dotted line E. It is not however necessary that this should be done at this
stage, but any other convenient stage of the process may be selected for doing it.
When the glass is cool I cut the tube in two across the neck at such a distance
from the end as to leave the two glass points projecting from the bottom piece of
the tube, as shewn at Figure 4. This division of the tube may easily be effected
by slightly scratching it with a file or cutting with a diamond, and applying a
hot iron or hot piece of glass. When this has been done the two hollow points at
the top of the projection B are opened in the blow pipe, or by breaking off their
ends, or in any other convenient way, and conducting wires are passed through
the openings so made and then sealed in the glass by means of white enamel, or
what is technically known as arsenic glass. If platinum wires are used to pass
through the glass for the purpose of acting as conducting wires, they can be sealed
into the glass in the usual way without the use of such enamel. The most con-
venient method of fixing the wires in the lamp is to coat them with enamel or
arsenic glass, and to pass each wire through a separate short cylinder of glass of
small section, and heating it in the blow pipe so as to melt the glass and enamel,
and then seal them together. A conducting wire having a short cylinder of glass
so sealed on to it is shewn at Figure 5. The wire is now passed through the open
point of the glass projection above mentioned until the glass cylinder on the wire
rests against the end of the glass projection, and the two are then sealed together
in the blow pipe either with or without the interposition of arsenic glass or
enamel the parts will then have the appearance shewn in Figure 6.
The carbon filament can now be attached to the conducting wires; afterwards
the two portions of the tube forming the lamp are sealed together in the blow pipe
at the place where the tube was cut open; the lamp is now in a fit condition for
exhaustion, which is effected through the small tube which has been sealed on to
it for the purpose, and when the exhaustion has been effected this tube is sealed
off, preferably close to the point of junction with the lamp; the finished lamp then
presents the appearance shewn in Figure 7.
The hollow at the base of the lamp may be filled with plaster of Paris or any
other like cement_for_the-purpose-of-giving-strength to the lamp, and protecting.
the conducting wires and their attachments. The pores of the cement may, if
thought advisable, be filled in with a fusible cement.
If a carbon filament in a lamp breaks, the neck of the lamp can be again cut
across and a fresh filament attached, and the lamp sealed up and exhausted or
filled with a protective atmosphere as before. It will however be convenient to
insert a small tube for exhaustion in one of the portions of the lamp before it is
opened, as it is more difficult to do it afterwards.
I sometimes form the metal tool used for forming the hollow projection B with
only one prong so as to form one hollow pointed projection into the neck, and
then seal in both the conducting wires near together but not touching. I also use
a metal tool with more than two prongs if I wish to have two or more filaments
together in the same lamp. I also in some cases make the ends of the prongs
chisel shaped instead of pointed, more especially if one prong only is used.
One of the chief difficulties in the construction of such lamps is the sealing in
of the wires. It is difficult to make a good junction between the glass and the
metal except in the case of platinum; and with thin conducting wires of platinum
the low conductivity of the metal causes it to heat when large currents are used,
and to crack the glass or cause a leak at the junction I get over this difficulty
by using a compound wire having a core of copper, silver, gold, or other good
conductor, and a platinum sheathing, so that I have the advantage either of using
a cheaper metallic conductor or a metallic conductor of better conductivity without
any increased difficulty in making it form a good junction with the glass. The

page_text: wire, whether compound or simple, may be used of a circular section; or in order
still further to diminish the liability to crack owing to unequal expansion it may
'be flattened out into a ribbon or curved, so that it is of a horse shoe form in cross
section.
For practical purposes it is of the greatest importance that lamps of this class
on the same circuit should all have the same resistance when in use. To accomplish
this I proceed as follows:-I attach the ends of the carbon filament to two small
hollow copper or platinum terminals, which are fiexd on a small bar of arsenic
glass or similar non-conductor so as to keep them at a suitable distance to fit upon
the extremity of the conducting wires. If the carbon filament is sufficiently
flexible to stand the necessary amount of manipulation I dispense with the bar of
arsenic glass. I then place the filament in an apparatus consisting of a bell shaped
receiver, which is in connection with an air pump and capable of being exhausted
by it. The plate upon which this receiver rests is of ebonite or similar non-
conducting substance, and is fitted with pairs of pointed wires in metallic con-
nection with binding screws or terminals on the outside of the apparatus. The
pointed wires of each pair are at the same distance from each other as the copper
or platinum terminals of the carbon filaments, so that a carbon filament provided
with the tubes above mentioned can be placed with its terminals on one of the
pairs of the pointed wires, and the copper or platinum tubes being slipped over the
ends of the wires a current is sent through it from the outside while the exhaustion
is going on.
It is of course not necessary that pointed wires should be used within the
apparatus, as any other form of pairs of terminals situated at the right distance
from one another will serve equally well; but if the ends of the carbon filament
are encased in metallic tubes in the manner described it will be found most
convenient to use these pointed wires. A convenient variation of the method is
by suspending the portion of the lamp marked B, in Figure 6, by the conducting
wires from pairs of terminals, the terminals in this case being fixed in a plate
forming the top of the receiver instead of the bottom.
The carbon filaments are placed in this apparatus, the appearance of which, with
the several carbon filaments, will be as shewn in Figure 8. The air is then
exhausted and a current is passed through each filament, and its resistance is
measured. when it is as nearly as possible under the same circumstances as in
finished lamps. If the resistance of any of the filaments is found to be too high,
the current is maintained through them, while some hydrocarbon vapour, or
chlorinated hydrocarbon vapour, or some other analogous compound is admitted
into the receiver by putting it into connection by means of a stop cock with a
vessel containing the hydro-carbon or the chloroform. Instead of chloroform,
naphaline, xylol, or some other hydrocarbon may be used, as described in my
Patent 1881, No. 2612. This causes a deposition of carbon on the highly heated
filament, and so soon as the resistance of any filament is reduced to the standard
amount the current is turned off from it and the deposition ceases.
A large
number of carbon filaments can be operated on at one time by this method.
In Figure 8 A is a glass vessel; B, a collar cemented into top of this vessel;
C, a thick plate, preferably of vulcanized fibre, fitting into B with a conically
ground joint; D, D¹, glass covered wires passing through C, ground conically and
cemented into place; E, mercury poured over top to prevent access of air; F,
lamp ends with filaments connected to them in electrical contact with D, D¹; G,
tube leading to exhaust pump; H, tube leading to vessel containing chloroform or
other substance. The tubes G and H should preferably both be fitted with taps.
The chloroform or hydrocarbon might be placed in a cup I.
The operation of regulating the resistance may be performed after the filament
is attached to the lamp and the lamp attached to the pump. If the lamp is
blackened in the operation it can be cut open, cleaned, resealed, and reexhausted.
In order to increase the rigidity of the carbon filaments I may make them of a
flat section, and give to them a twist of a quarter of a circle in placing them in

page_text: the terminals or ends of the conducting wires, so as to make the flat section at one
end of the filament perpendicular to the flat section of the other. The filament,
which is fixed in the shape of a horse shoe, will then be found to possess great
rigidity.
The improvements lastly described are chiefly practicable when the carbon is
very elastic and homogeneous, as in the case of carbon filaments manufactured by
means of the process described in the Specification of a Patent granted to me on
the 15th of June last, and numbered 2012.
I claim as my Invention,-
First. The process of forming the glass enclosures for the filaments of incan-
descent lamps, substantially as herein described.
Second. The process of forming a junction between the conducting wires of
electric lamps of the incandescent type and tho glass enclosures through which
they are passed, consisting in forming an internal projection or projections in the
glass enclosure by means of a tool with one, two, or more prongs or blades, then
perforating the inner end of the projection or projections to pass the wires through
them, and then sealing the wires to the ends of the projections, substantially as
herein described.
Third. The use of cored wires with an external platinum surface for conducting
wires at the points where they pass through the glass of the enclosures of
incandescent lamps, substantially as herein described.
Fourth. The arrangement of apparatus for enabling the regulation of the
resistance of carbon filaments for electric lamps on the incandescent principle to be
readily effected, substantially as herein described.
Fifth. The use of chloroform to produce a vapour from which carbon can be
deposited on the filaments of electric lamps on the incandescent principle;
substantially as herein described.
Sixth. The method of mounting the filaments of electric lamps, herein described,
for the purpose of giving to them greater rigidity.
In witness whereof, I, the said William Crookes, have hereunto set my hand
and seal, this Twenty fourth day of February, in the year of our Lord
One thousand eight hundred and eighty two.
MAYNA