IMPROVEMENTS IN ELECTRIC-LIGHTING APPARATUS
Year: 1880

page_text: LETTERS PATENT to William Robert Lake, of the Firm of Haseltine, Lake,
& Co., Patent Agents, Southampton Buildings, London, for an Invention of
"IMPROVEMENTS IN ELECTRIC-LIGHTING APPARATUS." A communication
from abroad by Joseph V. Nichols, of Brooklyn, New York, United States
of America.
PROVISIONAL SPECIFICATION left by the said William Robert Lake at
the Office of the Commissioners of Patents on the 3rd November 1880.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co., Patent
Agents, Southampton Buildings, London. "IMPROVEMENTS IN ELECTRIC-LIGHTING
APPARATUS.' [A communication from abroad by Joseph V. Nichols, of Brooklyn,
New York, United States of America.]
This Invention relates to that class of electric lamps or lighting apparatus known
as incandescent lamps, in which light is produced by the incandescence of a
continuous conductor of low conductivity forming a part of the electrical circuit of
the lamp.
When the conductor is made of carbon, which has been found to be the most
available material for that purpose, it is essential that it should be effectually
protected when highly heated from all access of oxygen, as it readily oxidizes at
high temperatures, and the incandescent part of the lamp has usually been enclosed
in a glass globe, from which the air has been exhausted or excluded. Various
devices have been used for making perfectly tight joints about the conducting
wires, but sealing the glass of the globe directly to the conducting wires bas
proved more effective and convenient for this purpose than other constructions.
Platinum has been considered the only available material of which to make the
conducting wires in lamps so constructed, as the coefficients of expansion of other
metals differ considerably from that of glass, and glass moreover does not readily
adhere to them. The firm adhesion of the glass to the metal is obviously essential
to a perfect joint, and the lamp undergoes very considerable changes of temperature
in use; any inequality in the coefficients of expansion of the parts tends to separate
them at the joint or to crack the glass about the wire, and even with a metal of the
same coefficient of expansion as the glass there is a considerable tendency to the

page_text: formation of cracks in the glass about the wires on account of the low thermal
conductivity of glass. The platinum wire becoming heated by conduction from
the incandescent carbon expands rapidly, while the adjacent glass conducting the
heat received from the platinum very feebly expands slowly, and the glass is
temporarily subjected to a strain which tends to crack it.
The use of platinum for conducting wires in such lamps is moreover objectionable
for other reasons. Its electrical conductivity is comparatively low, and as the
leading wires have to be made quite small when sealed into the glass they are more
or less heated by their resistance to the current, thereby aggravating the tendency
to crack the glass due to the expansion caused by the heat received from the
carbon. This metal moreover, as is well known, has a remarkable capacity for
absorbing gases, and oxygen thus occluded in the conducting wires is probably to
some extent given off again within the globe when the wires become heated, to the
injury of the incandescent carbon, and the expensiveness of platinum also adds
considerably to the cost of the lamp. It is obviously extremely desirable to use
for conducting wires a metal free from these objections, such as copper, and to
construct the globe in such a manner as to avoid the tendency to the formation of
cracks about the wires.
In carrying the said Invention into practice, I form the base of the glass globe,
or that part which immediately surrounds the conducting wires, of a composition
or cement made by mixing various metallic substances with silica and potash,
whereby the adhesion of the parts may be increased and the tendency to crack
diminished, and when proper proportions are used the composition or cement so
formed will readily adhere both to glass and to copper, and will not crack when
the parts are subjected to changes of temperature. The composition so formed is
apparently metallo-vitreous in its nature, being, in fact, neither metal nor glass,
but possessing for certain purposes the properties of both. I find that a serviceable
cement of this kind is formed by thoroughly mixing and fusing together fifty eight
parts by weight of oxide of lead, seventeen parts of silica, ten parts of oxide of
iron, ten parts of oxide of copper, and five parts of potash or soda. It is not
essential to use exactly the ingredients named, or to combine them in precisely the
proportions indicated, but it is essential that the cement should be rich in metallic
constituents and at the same time contain sufficient silica to insure perfect adhesion
to the glass of the globe. I prefer to use the cement for only a small part of the
base of the globe immediately adjacent to the conducting wires and to form the
main part of the globe of glass. The conducting wires are made preferably of
copper on account of its high electrical conductivity and its cheapness, but other
metals may be used if desirable. The absence of cracks in the base of a lamp so
constructed is probably due to the assimilation of the cement to the metal of the
wires, both as regards its coefficient of expansion, and as regards its thermal
conductivity, and to its being more tough and elastic than glass. The heating of
the conducting wires by the current is also largely avoided by constructing them of
metal of high electrical conductivity.
Tubes of the composition or metallo-vitreous cement, composed as aboyo
described, are fused and sealed to the conducting wires at their upper ends, and to
the glass of the globe at their lower ends, so that the base of the globe is
hermetically sealed about the said conducting wires. The tube of cement should
be joined to the wire when both are at a white heat so as to remove all oxide
from the surface of the metal and insure perfect adhesion between the parts. By
way of additional precaution a second joint may be made between the tube and
wire a short distance below the upper end of the tube. The air may be
exhausted from the globe in the usual way so as to leave as perfect a vacuum as
practicable, or the air may be replaced with a rarefied atmosphere of hydrocarbon
vapor or gas.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Robert Lake in the Great Seal Patent Office on the
30th April 1881.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, and Co., Patent
Agents, Southampton Buildings, London. "IMPROVEMENTS IN ELECTRIC-LIGHTING
APPARATUS." A communication from abroad by Joseph V. Nichols, of Brooklyn,
New York, United States of America.
This Invention relates to that class of electric lamps or lighting apparatus
known as incandescent lamps, in which light is produced by the incandescence of a
continuous conductor of low conductivity, forming a part of the electrical circuit
of the lamp.
When the conductor is made of carbon, which has been found to be the most
available material for that purpose, it is essential that it should be effectually
protected when highly heated, from all access of oxygen, as it readily oxidizes at
high temperatures, and the incandescent part of the lamp has usually been
enclosed in a glass globe from which the air has been exhausted or excluded.
Various devices have been used for making perfectly tight joints about the
conducting wires, but sealing the glass of the globe directly to the conducting
wires has proved more effective and convenient for this purpose than other
constructions.
Platinum has been considered the only available material of which to make tho
conducting wires in lamps so constructed, as the coefficients of expansion of other
metals differ considerably from that of glass, and glass moreover does not readily
adhere to them. The firm adhesion of the glass to the metal is obviously essential
to a perfect joint, and as the lamp undergoes very considerable changes of tempera-
ture when in use, any inequality in the coefficients of expansion of the parts tends
to separate them at the joint or to crack the glass about the wire, and even with a
metal of the same coefficient of expansion as the glass there is a considerable
tendency to the formation of cracks in the glass about the wires on account of the
low thermal conductivity of glass. The platinum wire becoming heated by
conduction from the incandescent carbon expands rapidly, while the adjacent glass
conducting the heat received from the platinum very feebly expands slowly, and
the glass is temporarily subjected to a strain which tends to crack it.
The use of platinum for conducting wires in such lamps is moreover objectionable
for other reasons. Its electrical conductivity is comparatively low, and as the
leading wires have to be made quite small when sealed into the glass they are
more or less heated by their resistance to the current, thereby aggravating the
tendency to crack the glass due to the expansion caused by the heat received
from the carbon. This metal moreover as is well known has a remarkable capacity
for absorbing gases, and oxygen thus occluded in the conducting wires is probably
to some extent given off again within the globe when the wires become heated, to
the injury of the incandescent carbon; the expensiveness of platinum also adds
considerably to the cost of the lamp.
It is obviously extremely desirable to use for conducting wires a metal free from
these objections, such as copper, and to construct the globe in such a manner as to
avoid the tendency to the formation of cracks about the wires. I therefore form
the base of the glass globe, or that part which immediately surrounds the conducting
wires, of a composition or cement made by mixing various metallic substances with
silica and potash, whereby the adhesion of the parts may be increased, and the
tendency to crack diminished, and when proper proportions are used the composition
or cement so formed will readily adhere both to the glass and copper, and will not

page_text: crack when the parts are subjected to changes of temperature. The composition
so formed is apparently metallo-vitreous in its nature, being in fact neither metal
nor glass, but possessing for certain purposes the properties of both. I form a
serviceable cement of this kind by thoroughly mixing and fusing together fifty
eight parts by weight of oxide of lead, seventeen parts of silica, ten parts of oxide
of iron, ten parts of oxide of copper, and five parts of potash or soda. It is not
essential to use exactly the ingredients named, or to combine them in precisely the
proportions indicated, but it is essential that the cement should be rich in metallic
constituents, and at the same time contain sufficient silica to insure perfect adhesion
to the glass of the globe. I prefer to use the cement for only a small part of the
base of the globe immediately adjacent to the conducting wires, and to form the
main part of the globe of glass. The conducting wires are made preferably of
copper by reason of its high electrical conductivity and its cheapness, but other
metals may be used if desirable. The absence of cracks in the base of a lamp so
constructed is probably due to the assimilation of the cement to the metal of the
wires, both as regards its coefficient of expansion, and as regards its thermal
conductivity, and to its being more tough and elastic than glass. The heating of
the conducting wires by the current is also largely avoided by constructing them
of metal of high electrical conductivity.
In the accompanying Drawing I have shewn a lamp constructed in accordance
with my Invention.
A is the incandescent conductor; B is the glass globe enclosing the conductor ;
C, C, are conducting wires of copper; D, D, are tubes made of cement, such as that
above described, fused and sealed to the conducting wires at their upper ends and
to the glass of the globe at their lower ends, so that the base of the globe is
herinetically sealed about the said conducting wires. The tube of cement should
be joined to the wire when both are at a white heat, so as to remove all oxide from
the surface of the metal and insure perfect adhesion between the parts. By way
of additional precaution a second joint may be made between the tube and the
wire a short distance below the upper end of the tube. The air may be exhausted
from the globe in the usual way so as to leave as perfect a vacuum as practicable,
or the air may be replaced with a rarefied atmosphere of hydrocarbon vapor or gas.
Having thus fully described the said Invention as communicated to me by
my foreign correspondents, and the manner of performing the same, I wish it
understood that I claim,-
First. The combination in an electric lamp of a glass globe enclosing an
incandescent conductor in a vacuum with conducting wires connected with the said
conductor and metallo-vitreous cement interposed between the glass of the globe and
the said conducting wires and united to both by fusion, substantially as above
described.
Second. In an electric lamp, a glass globe enclosing the incandescent or light
giving part in a vacuum, in combination with conducting wires of copper or other
inetal of high conductivity and metallo-vitreous cement interposed between the
glass of the globe and the conducting wires and united to both by fusion,
substantially as herein described.
In witness whereof, I, the said William Robert Lake, have hereunto set my
hand and seal, this Thirtieth day of April, in the year of our Lord One