Year: 1897

page_text: Date of Application, 23rd Aug., 1897
Complete Specification Left, 22nd Apr., 1898-Accepted, 28th May, 1898
I, WALTHER NERNST, Ph.D., of 50, Burgerstrasse, Gottingen, Germany,
Professor, do hereby declare the nature of this invention to be as follows:-
My invention relates to a new kind of electrical glow light; with the existing
constructions of glow lights conductors of the first class (metallic conductors, &c.)
serve as the resistances to be heated.
These are, however, in principle, unsuitable, because they strongly absorb, besides
light, also all the ultra red rays, and consequently also when incandescent they
preferentially emit these, so that only a small portion of the electrical energy
supplied is regained as light.
When using conductors of the second class (electrolytes) as incandescence bodies,
it is, in principle, possible to find out a material that, when incandescent, will,
at least preferentially, emit rays of such a wave-length as to be sensible as light;
tho excellent action of the Welsbach light for instance, appears mainly to be
based upon such a behaviour of the incandescence bodies employed.
As a matter of fact, it is possible to bring substances such as lime, magnesia,
and the like to an intense white heat by means of suitable currents, and measure-
ments have proved, as was to be theoretically forseen, a considerable superiority
of the new electric glow lights as compared with those hitherto employed.
The circumstance that the said substances permanently withstand very high
temperatures, of course contributes to the farther increase of the useful effect.
For example a small hollow cylinder of burnt magnesia of 7 milimetres length,
15 m.m. thickness and about 0'4 mm. internal diameter, when heated to incan-
descence in the open air, gives with an alternating current of 0.23 Amperes and
118 volts pressure (equal to 27 Watts), 31 Hefner lamps = 26 normal candles,
It is not to be doubted that with the
therefore, per Watt 0.96 normal candles.
use of larger incandescence bodies, and correspondingly stronger currents as also
by the use of exhausted globes, or globes filled with gases that act as bad con-
ductors of heat, the useful effect would be considerably raised.
The said conductors when at ordinary temperature are almost perfect insulators,
and it is only when they are highly heated that they begin to act as comparatively
good conductors. In order therefore to be able to pass the electric current (whether
alternating or continuous current) through the incandescence body, a preliminary
heating is necessary, which can be readily effected either by a flame or by an
electric spark-current sent through the tubular incandescence body, or in any
other suitable manner.
Under certain circumstances a simultaneous employment of flame-heating
together with the electric heating may be advantageous, as by this means an
exceedingly bright light can be attained with the consumption of only a com-
paratively small amount of electrical energy.
Dated thin 22nd day of August 1897.

page_text: I, WALTHER NERNST, Ph.D., of 50, Burgerstrasse, Gottingen, Germany,
Professor, 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 a new and improved kind of electric incandescent light.
The invention consists in substituting for the conductive substance forming
what is generally called the filament of the lamp a substance which at the ordinary
temperature is a nonconductor and only becomes a conductor at the high tempera-
ture of incandescence.
It has been known before to those conversant with the art, that certain oxides,
sulphides, fluorides, silicates, and other salt like compositions of metals are
specially qualified to emit light when heated to a high temperature and such
bodies have therefore been repeatedly used to coat or impregnate the carbon usually
constituting the filament of electric incandescent lamps.
These bodies however have been looked upon heretofore as non-conductors of
the electric current and therefore inventors have always supplied special means
for heating them when employed as incandescent bodies in electric lamps.
Now I have discovered that a large number of these bodies, which may be
classified under the general expression of electrolytes or of conductors of the
second class (as compared with conductors such as metals or carbon, which
conduct the current without any electrolytic action taking place and which are
classified as conductors of the first class) when used in a dry state though they
are almost perfect non-conductors when cold, acquire so high a conductivity when
once heated to an incandescent state, that a current of sufficient strength can be
passed through them at ordinary low electrical pressures to keep them in the
incandescent state.
The advantage gained by the use of dry electrolytes instead of ordinary con-
ductors for the filaments of glow lamps are twofold. Firstly a considerably
higher efficiency is obtained, because these bodies emit more light for an equal
consumption of energy than any known filament, ranging in fact very much
nearer the arc lamp in this respect than the ordinary glow lamp and in some
cases even surpassing it.
Secondly the specific resistance of these bodies varies so much with the tempera-
ture that within practical limits a filament, of any dimensions can be used at any
desired absolute resistance and consequently my lamps can be burned at much
higher voltages than ordinary glow lamps, thus causing a considerable reduction
of copper section in the conductors.
I have found by experiment, that the oxides of magnesium, of zirconium and
of rare earths are specially well adapted for the use indicated.
The accompanying drawing is a side view partly in section of one form of my
lamp, and a means for heating the incandescent body.
In the drawing B+, B- indicate binding posts being connected with any source
of electricity setting up a pressure of for instance 100-200 volts between them.
S+, S are two elastic strips of metal of suitable section.
I is a small cylinder made of magnesia or any other suitable dry electrolyte 4
which itself forms the incandescent body of the lamp and the conductor between
S +, S Preferably cylinder I is not enclosed in an air tight globe but is open
to the air, but this is not essential.
The operation of this lamp is as follows.

page_text: When the pressure is set up in the binding posts, no current can pass through I
because when cold its resistance is equal to many thousands of ohms.
But as soon as the temperature of I is sufficiently raised, for instance by applying
a powerful gas flame 4 for a few seconds, the conductivity of I is raised and con-
sequently a current is set up which immediately takes upon itself the function
of the flame and continues supplying the amount of heat which is being dissipated
by radiation. Therefore the flame can be withdrawn and the lamp will continue
to glow like any ordinary electric glow-lamp. A. Bunsen burner 1 is shewn
below cylinder I for heating it. 2 is a flexible gas tube leading to the burner,
and 3 is a cock for turning on and off the gas.
The base of the electric lamp
has a centrally located recess 5 into which the base of the gas burner may be
set. This serves to properly locate the gas burner.
In some cases I prefer not to withdraw the flame but to continue heating the
body I by a flame and by the current simultaneously, thus obtaining a compara-
tively high amount of light with an exceedingly low expenditure of electrical
energy because the flame creates an atmosphere of very high temperature around
the incandescent body and thereby considerably reduces the loss of heat.
Having now particularly described and ascertained the nature of my invention
and in what manner the same is to be performed, I declare that what I claim is:-
1. An improved electrical incandescent lamp, in which the filament is composed
of a substance, preferably a dry electrolyte such as for instance magnesia, which
is an almost perfect non-conductor when cold and becomes a fairly good con-
ductor, when heated to incandescence, substantially as and for the purpose
described.
2. In an electric glow-lamp the filament of which is composed of a dry
electrolyte the method of starting such lamp, which consists in applying any
known means of heating said filament, until its conductivity is sufficiently
raised to enable it to conduct a current applied at the ordinary low pressures,
substantially as and for the purpose described.
3. In electrical glow-lamps the filament of which is composed of a dry electrolyte
the method of keeping such filament in the incandescent state by heating it with
a flame and by means of an electric current simultaneously passed through it,
substantially as and for the purpose described.
3