Improvements in Incandescent Electric Lamps.
Year: 1893

page_text: Date of Application, 7th Mar., 1893
Complete Specification Left, 7th Dec., 1893-Accepted, 27th Jan., 1894
PROVISIONAL SPECIFICATION.
Improvements in Incandescent Electric Lamps.
GILBERT SCOTT RAM 32 Oakley Square, London N.W. Engineer do hereby
declare the nature of this invention to be as follows:-
It is well known that ordinary incandescent electric lamps are usually provided
at the terminal end with an external cap in order to facilitate the making of the
electrical connection and to secure the firm support of the lamp. Such a cap is
not a part of the lamp but is a separate attachment. It is frequently formed of a
short length of brass tube filled up with plaster of paris, two metal contact plates
being imbedded in the plaster so as to expose their upper surface flush with the
plaster and the end of the brass tube. These metal plates are connected by wire
to the platinum leading-in wires of the lamp. These caps are however sometimes made
wholly or in part of a material called vitrite, but are affixed to the lamps in a
similar manner by means of a suitable plaster. The caps usually carry two pins,
one on each side. When a lamp capped with such a cap is inserted in a lamp
holder the two pins slide in a bayonet joint in the barrel of the holder and at the
same time contact springs in the holder press upon the metal contact plates in the
cap thereby making electrical contact to the lamp.
The object of my invention is to dispense altogether with the cap, but at the same
time to make a lamp which can be used in the ordinary lamp holders such as are
commonly in use for lamps with caps.
In order to carry out my invention, instead of making the terminal end of my
lamp of a convex form as is usual, I make it concave or cup-shaped.
I may do this by sealing the leading-in wires carrying the filament a short
distance up the neck of the bulb instead of at the end. This may easily be
accomplished by previously melting some glass round the leading-in wires and
afterwards melting this glass, with the leading-in wires to which the filament is
attached passing through it, to the inside of the neck of the bulb at a sufficient
distance from the end of the neck.
This however is not in itself new, having been done in some of the early types
of lamps.
Having however made the terminal end of my lamp concave or cup-shaped with
the platinum leading-in wires passing into the lamp at or near the bottom of the
cup, I solder or otherwise connect electrically two metal contact plates similar to
those used in caps one to each leading-in wire either directly or by means of a
piece of copper or other wire. On opposite sides of the hollow cup I make a hole
through the glass. Through each of these holes I insert loosely a short pin similar
to those on the caps previously mentioned. The pin may have a flat plate or a
head on the inside. Having done this I fill the cup to the top with a suitable
plaster taking care to keep the contact plates flush with the surface of the plaster.
When the plaster has set the contact plates and the side pins will be firmly fixed
in position. The outside diameter of the hollow cup or neck of the lamp is about
the same as that of the ordinary cap. It will thus be understood that I can insert
my lamp into the usual form of lamp-holder and it will be held there by the side
pins and will be electrically connected precisely as well as though it was capped in
the usual manner. By making the lamp thus, I save the expense of the vitrite or
brass cap, besides making the lamp lighter in weight and neater in appearance.
As I have found that ordinary plaster of paris expands in setting so much as
sometimes to crack the glass in which it is contained I prefer to use with the
plaster of paris a small proportion of slaked lime which I find has the effect of

page_text: preventing this action. In order at the same time to make the plaster harder than
ordinary plaster-of-paris I may add a small percentage of dextrine which I find
makes it very hard. I may however use any other suitable plaster. Moreover
I do not confine myself to the method described for making the glass cup at the
end of the lamp. I might for instance seal the filament in the bulb in the ordinary
way and then melt on a piece of glass tube, which could then be cut off to the
required length & filled up with plaster as in the other case. This piece of
tube being melted on would be equally part of the lamp and not a separable
attachment.
Dated this Seventh day of March 1893.
COMPLETE SPECIFICATION.
Improvements in Incandescent Electric Lamps.
GILBERT SCOTT RAM 32 Oakley Square London N.W. Engineer 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:-
It is well known that ordinary incandescent electric lamps are usually provided
at the terminal end with an external cap in order to facilitate the making of the
electrical connection and to secure the firm support of the lamp. Such a cap is not
part of the lamp but is a separate attachment. It is frequently formed of a short
length of brass tube filled up with plaster of paris, two metal contact plates being
embedded in the plaster so as to expose their upper surface flush with the plaster
and with the end of the brass tube. These metal plates are connected by wire to
the platinum leading-in wires of the lamp. These caps are however sometimes made
wholly or in part of a material called "vitrite," and are attached to the lamps by means
of a suitable plaster or cement. The caps usually are provided with two projecting
pins, one on each side. When a lamp, fitted with such a cap, is inserted in a lamp
holder, the two pins engage in a bayonet joint in the barrel of the holder and, at
the same time, contact springs in the holder press upon the metal contact plates in
the cap, thereby making electrical contact to the lamp.
The object of my invention is to dispense altogether with the cap, but at the
same time to make a lamp which can be used in the ordinary lamp holders, such as
are commonly in use for lamps with caps.
In order to carry out my invention, I make the end of my lamp into the form
of a cup.
The leading-in wires pass through the bottom of this cup-shaped end
of the famp. The ends of the leading-in wires are connected either directly or by
another piece of wire to metal contact plates, one to each wire. The cup-shaped
end of the lamp is externally of such a diameter that it will pass easily into the
barrel of an ordinary lamp holder. On opposite sides of the cup, I make a hole.
In each. of these holes I insert a pin, from the inside, having a head or enlarge-
ment on the inner end. I then fill up the space within the cup with a suitable
plaster, which, on setting, holds the contact plates and the side pins firmly in
position, the outside surface of the contact plates and the plaster being flush with
the end of the cup.
It will thus be evident that the lamp so constructed is capable of being used in
exactly the same way as though it was an ordinary lamp with a cap attached to it.
It can be inserted in the usual form of lamp-holder and it will be held by the side
pins in the bayonet joint and will be electrically connected to the contacts in the
holder precisely as though it were a lamp with an external cap attached. By
making the lamp thus I save the expense of the metal or vitrite or other cap, while
the lamp is lighter in weight and neater in appearance.
The lamp may be formed, with the cup-shaped base, in several different ways,

page_text: for instance, as shown in Fig. 1 of the accompanying drawings. The lamp bulb A
is blown with its neck, B, of such a diameter as to fit easily within the barrel of
the lamp-holders in which it is intended the lamp shall eventually be used. Two
holes are made in the neck, B, opposite. each other for the reception of the side
pins. These holes may be inade by softening the glass at the required spot with
the blow-pipe flame and then blowing the glass outwards or punching out a piece
of the glass with a suitable instrument. The leading-in wires CC are wound
round with soft glass forming a disc of such a diameter that it is just able to pass
into the neck B. This disc C carrying the leading-in wires with the filament
attached is then sealed into the neck of the bulb B at the required distance from
the end by means of the blow-pipe flame. The neck B of the bulb may be cut
off to the required length either before or after the scaling-in. The neck of the
lamp thus forms a cup, through the bottom of which, D, the leading-in wires pass
into the lamp.
Another method of forming the cup-shaped end is as follows. The filament is
sealed into the lamp in the ordinary way. In this case the neck of the bulb may
be very short or there may be no neck. A piece of glass tube, E, Fig. 2, of the
required diameter is then melted on to the base of the lamp, enclosing the
leading-in wires C C. The holes for the side pins are made and the tube is cut off
to the required length.
Another method for forming the cup-shaped end is shown in Fig. 3. The
leading-in wires are sealed through the end of a piece of glass tube, G, of the
required diameter. The filament is preferably attached to the wires after the wires
are sealed into the tube.
The tube G, carrying the leading-in wires with the
filament attached, is then sealed into the bulb A. The side holes are made and
the superfluous tube is cut off.
The filament being sealed in the bulb with the wires passing through the bottom
of the cup-shaped end, the lamp may be exhausted in the usual manner. Two
metal contact plates, H H, are then attached to the leading-in wires by soldering or
otherwise, one to each wire. In each of the holes in the side of the cup is inserted
a pin, KK, having a head on the inside. The cup is then filled up with a suitable
plaster, M, taking care that the contact plates are kept flush with the end of the
cup. When the plaster has set, the contact plates and the side pins will be
firmly held in position. The end of the lamp may, if desired, be ground so as to
ensure that the plaster and the contact plates are perfectly level with the rim
of the cup.
Instead of making holes in the sides of the cup and inserting pins therein, I may
make projections on the cup by fusing small lumps or knobs of glass upon it, or
pins of metal may be directly fused into the glass.
As I have found that ordinary plaster of paris expands in setting so much as
sometimes to crack the glass in which it is contained, I prefer to use with the
plaster of paris a small proportion of slaked lime which I find has the effect of
preventing this action. In order at the same time to make the plaster harder than
ordinary plaster of paris, I may add a small percentage of dextrine, which I find
has the desired effect. I may however use any other suitable plaster.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is :-
An incandescent electric lamp having contact plates secured by plaster or cement
within the base of the lamp itself capable of being used in an ordinary bayonet-
joint spring-contact or similar holder."
GILBERT S. RAM.