Improvements in and in the Manufacture of Incandescent Electric Lamps.
Year: 1892

page_text: COMPLETE SPECIFICATION.
Improvements in and in the Manufacture of Incandescent Electric
Lamps.
I, DEMETRIUS VON MITO, of 39 Schöneberger Ufer, Berlin, in the Kingdom
of Prussia, German Empire, Gentleman do hereby declare the nature of this
invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
My invention relates to improvements in the manufacture of incandescent lamps
and the object of my improvements is to reduce as far as possible the amount of
platinum wire required for each lamp. A characteristic feature of my invention is
that the platinum wire serves only for conveying the electric current through the
glass and is not employed either for securing the carbon filament nor the conducting
wires; the electric contact, inside the bulb, as well as outside the is effected
by means of an alloy in the manner fully described hereinafter.
The whole process is remarkable by its simplicity and by the good results
obtained.
same,
Before describing my invention specifically with reference to the drawings I will
first briefly state the different stages of the same.
Two pieces of platinum wire are secured to the glass bulb by bringing the glass
to a viscid state after inserting the said wires through two small tubes formed on
the glass bulb. Hereafter a suitable alloy being more fusible than glass and
having a co-efficient of expansion about equal to that of glass is brought into the
bulb through an opening left in the top of the same, and the space around the
inward ends of the platinum wires is filled with this alloy. By the application of
heat the alloy is then brought to fusion and the wires to which the carbon filament
is attached, are entered into the molten mass and kept in their due position till the
alloy has become solid. Thereupon I take small metal caps which are filled with
the same alloy and after having melted the alloy I bring the caps over the small
tubes from which the platinum wires project and when the metal has cooled, all
contacts are effected in a very durable manner and the air may then be exhausted
from the lamp.
In the accompanying drawings
Fig. 1 shows the form of glass bulb which I prefer to employ..
Fig. 2 represents the lower part of the same after the platinum wires are
inserted.
Fig. 3 shows the wires to which the carbon filament is secured and a holder
for these wires.
Fig. 4 shows the carbon filament in connection with the wires and holder.
Fig. 5 represents the glass bulb with the carbon filament secured in the same by
means of the alloy.
Fig. 6 shows one of the metal caps.
Fig. 7 shows the lamp with the conducting wires secured thereto.
Fig. 8 shows a form of the lamp in which a special socket may be dispensed with.
Figs 9 & 10 represent two forms of sockets.
Similar letters refer to similar parts throughout the different views.
The glass bulbs a which I prefer to employ, are of a particular form, but can be
manufactured in great quantities by blowing the glass in moulds in the same manner
as it is usual with the glass bulbs with the ordinary pattern.
The new bulbs, Fig. 1, are provided with a short and wide tube o at the top and
with two narrow tubes r at the bottom. Into these tubes r I introduce short length
of platinum wire so that they project out of said tubes about half their own length.

page_text: The length of these wires c may be about half an inch and the thickness of the wire
may be such, that 30 feet of the same weigh about dram. Hereafter the tubes r
are heated till the glass begins to melt and in this manner they are firmly secured
to the glass bulb a (Fig. 2). The carbon filament d (Fig. 4) is secured to wires e
of any suitable metal and in order to keep these wires equally apart, I employ a
glass rod or holder b (Fig. 3) as it is usual in the manufacture of incandescent
lamps. The connection between the wires e and the filament d is effected in the
ordinary manner by winding the extremities of the wires e spirally and inserting
the ends of the carbon filament into these wire spirals. The connection_is
improved by either depositing carbon by means of an electric current or by
employing a glue or cement which is a good conductor of electricity. It is
preferable that the wires e should be the same distance apart as the platinum
wires c.
In order to secure the carbon filament within the lamp I employ a particular
alloy which has the same co-efficient of expansion as glass. This alloy consists
of about 95% of tin and 5% of copper; the alloy may be rendered more or less
fusible by adding besides 1-0, 5% of lead or zinc.
The alloy is made in or cut into small rods and pieces wherewith the tubes r
are filled through the top tube o, hereafter the tubes are heated by means of a
Bunsen-burner which is held at about 4 inches below the bulb. The alloy will
melt soon and then the carbon filament and the wires e secured thereto are
brought into the bulb e through the open tube o and the wires e are immersed
in the molten alloy (Fig. 5). Then the burner is removed and the alloy cools
very rapidly so as to solidify and to firmly hold the wires e, which are imbedded
in the same. At the same time a very reliable electric connection is obtained
between the platinum wires c and the wires e. As the alloy adheres very intimately
to the glass and to the platinum wires it is almost impossible that air should get
into the bulb a after the same has been closed.
'
In order to obtain an equally good contact between the platinum wires c and the
exterior conducting wires, which are generally of copper, I employ metal caps s
preferably of the form shown at Fig. 6. These caps are filled about to the half
with the alloy, which I have already described and after melting the alloy in
the
caps s I bring the tubes r and the conducting wires w into the molten metal
(see Fig. 7).
The alloy solidifies very rapidly and thereby I obtain at the same time a good
transmission of the current and a firm connection between the conducting wires w
and the platinum wires c.
The lamp is then ready for the further treatment in the ordinary manner, that is
to say, the air is exhausted through a small channel left at the top by melting and
contracting the orifice o and when a suitable degree of vacuum is obtained, the
tube o is closed completely.
The different parts constituting the lamp's socket may be secured in the ordinary
manner by means of a coating of plaster of paris. The conducting wires are of
course secured to the corresponding parts of the socket; sockets of any form may
be employed and the lamp may even be used without a socket as shown by Fig. 8,
where the metal caps s are provided with small eyes t to which the conducting
wires may be secured directly. In this case a good contact may be insured by
means of springs pressing the conducting wires against the eyes t.
The plaster of paris which is employed for securing the lamp to its socket is
dried only after 3-6 days and it sometimes occurs that only lamps without sockets
are available and must be made ready for use in a short time. In this case the
construction shown at Fig. 9 & 10 may be employed with advantage.
A piece of cork k is provided with holes for the reception of the caps s and
tubes and fitted over the same, the socket u is then pushed over the piece of cork
and at the place of contact between the socket and the glass bulb k I employ a
layer of plaster of paris of the thickness of about half a line. This thin layer dries
very rapidly. Lamps of the Edison pattern may be provided with a layer of

page_text: plaster of paris on the caps s and the piece of cork k.
use in this manner within 6 hours.
A lamp may be fitted for
Having now particularly described the nature of my said invention, and in what
manner the same is to be performed, I declare that what I claim is :-
1. An incandescent lamp consisting of the combination of parts substantially as
hereinbefore described.
2. In an incandescent lamp as above claimed, a glass bulb provided with two
tubes for the reception of the platinum wires c, substantially as described with
reference to the accompanying drawings.
3. In incandescent lamps as above claimed, an alloy for imbedding therein the
ends of the platinum wires, of the conducting-wires, and of the wires holding the
carbon filament, consisting of the metals herein stated, to be used in about the pro-
portions specified.
4. In an incandescent lamp as above claimed, the metal caps s containing an
alloy in which are imbedded the exterior ends of the platinum wires and the ends
of the conducting-wires, substantially as described with reference to the accompany-
ing drawings.
5. In an incandescent lamp as above claimed, a lamp-socket constructed substan-
tially as shown in Figs. 9 & 10 of the accompanying drawings and described with
reference thereto.
6. The hereinbefore described process of manufacturing incandescent lamps,
substantially as set forth.
Du this 90th day of November 1805
DEMETRIUS VON MITO,
By Geo. Thos: Hyde,
4, Moorfields, Fore Street, London, E.C., Agent for the Applicant.