Improvements in Electric Incandescence Lamps.
Year: 1898

page_text: Date of Application, 12th Mar., 1858
1000
OUIL
4000
PROVISIONAL SPECIFICATION.
Improvements in Electric Incandescence Lamps.
I, Dr. WALTHER NERNST, Professor, of 50, Bürgerstrasse, Gottingen, Germany,
do hereby declare the nature of this invention to be as follows;-
-
This invention relates to the choice and composition of the materials, which I
find to be best fitted for the use as filaments of electric glow lamps.
In a former Application for Letters Patent filed August 23rd 1897 No. 19424
I have described a novel kind of glow lamp, the essential feature of which consists
in this, that the filament or incandescence body of this lamp is not made of an
ordinary conductor such as metals or carbon but of a dry electrolyte, such as the
oxides, sulphides, fluorides, silicates of metals and the like. These bodies are almost
perfect nonconductors of the electric current, when cold, but when heated to incan-
descence, become such good conductors, that they can be kept incandescent for an
indefinite time by an electric current passing through them at an ordinary work-
ing pressure.
In another Application for Letters Patent, filed October 12th 1897 No. 23470
I have described certain means for heating the filaments of such glow, lamps and
thereby starting them or making them fit to conduct a low pressure current.
I have now found by experiment that the oxides of metals as for instance of
magnesium, beryllium, zirconium and others, though they emit an exceedingly
large proportion of the energy received, in the shape of light, nevertheless are not
very well adapted for the use as filaments of electric lamps, when in a pure con-
dition, because their conductivity increases very slowly with the temperature.
Thus for instance a filament made of pure magnesia is a very fair insulator even
at temperatures surpassing 1000° Centigrade. Thus in order to use such bodies
as filaments of incandescence lamps it becomes necessary to provide very powerful
means for heating up such bodies before they will allow the electric current of
ordinary pressure to pass. Another drawback encountered with the use of filaments:
made of pure bodies is that such bodies, as is well known, have a very clearly defined
melting point. The effect of this circumstance is that filaments made of such
bodies are peculiarly liable to suffer from breakage and other mechanical faults,
because the temperature will rise considerably above the average at the points of
rupture as the electric resistance is highest at such points and when once it surpasses
the melting point, the filament will fall to pieces.
Now I have further found by experiment that these difficulties are not
encountered, when instead of using the pure bodies, impurities of almost any
kind are added to them or even if different chemically pure bodies are mixed
together.
Thus for instance magnesia, by an admixture of only a few per cents. of boric
acid, chloride of calcium, tungstic acid, or the like, has its conductivity increased
to such a degree, that with a pressure of about 100 volt at the terminals of the lamp,
the current will start if the filament is only. warmed with a weak flame such as for
instance the flame of a match. The same holds good for the mixtures of various

page_text: bodies, and I have found that especially the mixtures of the oxides of the rare
earths are well adapted for the specified purpose. The oxides of metals moreover
I find to be the only bodies that will withstand the effects of the atmosphere at
the high temperature of incandescence without being seriously affected.
Furthermore I obtain another very important advantage by the use of mixtures
instead of chemically pure bodies, which results from the peculiarity of mixtures
not to pass suddenly out of the solid into the liquid state, but to soften gradually,
when heated, like wax. Thus a filament formed of a mixture of oxides of rare
earths when ruptured by any mechanical influence will not be destroyed by the
action of the current, but on the contrary the higher temperature generated at the
point of rupture in consequence of the higher electric resistance at this place will
soften the material of the filament gradually to a welding state and the rupture
will thus be automatically healed.
Dated this 12th day of March 1908
ABEL & IMRAY,
Agents for the Applicant.
I, Dr. WALTHER NERNST, Professor, of 50, Bürgerstrasse, Göttingen, Germany,
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:-
This invention relates to improvements in that description of incandescence
bodies for electrical incandescence lamps in which the said incandescence body
does not consist of a conductor of the first class but of a conductor of the second
class.
The present improvements consist in the selection and combination of those
substances which I have found to be most suitable for the production of such incan-
descence bodies.
I have found from experiments that incandescence bodies of the above mentioned
kind, when made of pure substances only attain a sufficient conducting power to
act as an incandescence body when raised to a very high temperature, but that
when these bodies are mixed either with each other or with certain other substances,
the conducting power rises considerably more rapidly with the increase of
temperature.
Thus pure oxides, such as those of magnesium, beryllium, zirconium, thorium,.
yttrium, and the like, still act as comparatively good insulators even when heated
to 1000° C. But if there be added to them certain other substances, or even if
two or more such bodies be mixed together, their conducting power will be very
greatly increased. Pure magnesia for example, can only be brought with great
difficulty to a state of electrical incandescence, but if only a small percentage of
boric acid, calcium chloride, tungstic acid, or other suitable substance be added,
the conducting power is increased to such an extent by heating, that rods or
filaments made of such materials can be rendered incandescence, conductors with
a pressure of 100 volts and less, even when only warmed with a slight flame, such
as that of a match.
Only bodies formed of oxides are enabled to permanently withstand the energetic
action of oxygen at high temperatures, and in particular oxides of zirconium, and
the rare earths related thereto, have given excellent results as regards durability,
good light emitting power, and excellent conducting power.

page_text: Thus bodies composed of zirconium oxide with an addition of about five per cent.,
or slightly more, of yttrium oxide are very efficient; also bodies composed of
thorium oxide with an addition of about 20 per cent. of yttrium oxide, and bodies
composed of thorium oxide containing 3 per cent. of zirconium oxide, 3 per cent.
of yttrium oxide and 03 per cent. of cerium oxide afford very excellent results. Small
quantities of erbium oxide and didymium oxide may also be advantageously mixed
with the above mentioned bodies."
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, I declare that what I
claim is:-
1. Manufacture of electrical incandescence bodies from metallic oxides for electric
glow lamps, consisting in the admixture with pure metallic oxides of the kind
herein referred to either of other pure metallic oxides or of substances, for
the purpose of increasing the conducting power of such bodies when heated, sub-
stantially as described.
.'
2. In the manufacture of electrical incandescence bodies such as are referred to
in the first claim, the use of mixtures consisting mainly of zirconium oxide com-
bined with one or more of the rare earths related thereto, substantially as described.
3. In the manufacture of electrical incandescence bodies such as are referred to
in the first claim, the use of mixtures consisting mainly of either zirconium oxide
or thorium oxide, or a mixture of these, together with a small admixture of either
yttrium oxide, cerium oxide, erbium oxide, or of two or more of these combined,
substantially as described.
Dated this 8th day of December 1898
ABEL & IMRAY,
Agents for the Applicant.