Improvements in or relating to Electric Incandescent Lamps,
Year: 1899

page_text: Date of Application, 20th Sept., 1899-Accepted, 2nd Dec., 1899
[Communicated from abroad by ALF SINDING-LARSEN, of Fredriksvaern, in the
Kingdom of Norway, Electrical Engineer.]
Improvements in or relating to Electric Incandescent Lamps,
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 322, High Holborn, in the County of Middlesex, 6, Lord
Street, Liverpool, and 6, Bank Street, Manchester, both in the County of
Lancaster, and Lower Temple Street, Birmingham, in the County of Warwick,
Civil Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
As is wellknown, the electric incandescent lamps already in use consist of
an exhausted sealed glass vessel into which platinum wires are fused which
wires form the electric connection from outside with the incandescent (usually
carbon) filament inside the glass vessel. In order to prevent this carbon filament
from burning, which would occur if the glass vessel were filled with air. for
instance, it was necessary for it to be exhausted. The rapid volatilisation, how-
ever, to which the filament is subject at the temperature necessary to produce
a powerful light, evidenced by the inside of the vessel becoming blackened
with the separated carbon when the incandescent lamp has been long in use
is a great defect of such lamps. At the same time the disposition of the
filament to evaporation which the exhaustion of the globes produces, causes the
temperature to which the filament can be heated without breakage by volati-
lisation to be considerably reduced, which means a diminution of the light
attainable.
Attempts have been made to improve incandescent lamps so that instead of
completely exhausting the glass vessel there may be some hydrogen remaining
in it, but this process has led to no particular results.
In the present invention the glass bulb is filled with a gas (or gases) under
tolerably high pressure, which gases must be of such a nature that they do not
attack carbon even at the highest temperatures, as for instance argon, or
nitrogen. The glass vessel must of course be of suitable strength. The minimum
pressure in the lamp when the same is in action may be taken to be about
4 atmospheres.
By this means, 1) the duration of the lamp is considerably prolonged while
the filament volatilises with difficulty in such a dense atmosphere and 2) that
the light obtained is considerably increased as the filament can be heated to
a far higher temperature without breaking.
The gases or vapours to be used must be unaffected both chemically as also
physically, that is they must neither react chemically on the filament nor be
absorbed mechanically by it, the pressure of the gas must operate exclusively
on the outside of the filament. If the gas is forced into the interior of the

page_text: filament the desired effect will not take place; this consists in pressing together
the molecules of the filament from the outside so that they cannot break
away.
In a modification of the invention quick silver vapour is used as such neutral
gas. A lamp of this kind is preferably made of a tube bent in the shape of
a U instead of the ordinary glass bulb; in this tube the carbon
or other
filament is so enclosed that the end of the tube grip the pole wires. In the
exhausted interior of the tube there is a little drop of quicksilver which when
the filament is rendered glowing by means of the current, is quickly evaporated
and produces the desired high pressure atmosphere.
As at the commencement of the incandescence there is no pressure of gas
and for this reason the filament could consequently be easily damaged by the
strong heat, the lamp can be connected with a resistance apparatus so that at
the beginning a resistance is inserted so that the filament is only incandesced
slightly until the quicksilver is in the form of vapour when the full current
is switched on.
The same result may be attained in an even simpler manner by connecting
together two lamps (or two groups of lamps) by double wiring, so that at
first the two lamps (or groups of lamps) are connected in series (whereby only
slight incandescence arises) and afterwards connected in parallel in order to
produce complete incandescence.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, as communicated
to me by my foreign correspondent I declare that what I claim is: -
1. In electric incandescent lamps having filaments capable of volatilisation
enclosing the filaments in glass vessels which are filled with a gas or gases
under high pressure; said gas or gases being neutral both chemically and
physically even at the highest temperatures, for the purpose of preventing the
filament from volatilising and enabling high temperatures to be employed.
2. An electric incandescent lamp as set forth in Claim 1, in which the high
pressure atmosphere consists of quick silver vapour.
Dated this 20th day of September 1899.
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.