Improvements in the Manufacture of Incandescing Media for Lighting Purposes.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Incandescing Media for Lighting
Purposes.
I, RUDOLF LANGHANS, of 12B, Elisabeth Strasse, Berlin, in the. German Empire,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to the manufacture of incandescing bodies for use in
gas-lighting, or of skeleton bodies, which, when clothed with incandescing sub-
stances, are adapted for use in like manner; the product being in either case
characterised by firmness combined with elasticity.
Taking the original process of Auer von Welsbach as a basis of operation, my
improved method results in the production of a peculiar compound, wherein
thorium oxide, occurring as the basic component, is combined with silicic acid
and zirconium oxide, as the acid components, cerium oxide co-operating.
In the preparation of a skeleton frame or support, I employ Auer von Welsbach's
process, using a solution of thorium nitrate, zirconium nitrate and a nitrate of
an alkali (or of equivalent salts of the metals named) in an aqueous solution of
silicic acid, the ingredients being mixed in predetermined proportions, and at the
same time make use of a high-pressure gas-flame, a body partaking of the nature
of glass resulting. The elements of the acid components, viz., the silicic acid and
zirconium oxide, are in the proportion of 1 molecular weight-unit each, and the
element of the basic component, viz., thorium oxide, is in the proportion of not
less than 4 molecular weight-units. The partial or total substitution for one of
the acid components of a proportionate additional quantity of the other is con-
ducive to the production of a friable or a readily softening mass. A reduction of
the amount of thorium oxide precludes the formation of a body suitable for
practical purposes; while very high proportions of thorium have the effect of
rendering the material more brittle or apt to crumble to powder, and of thus
impairing the strength of the structure. The omission of the alkali, again, will
result in a friable rather than a vitreous product.
Provided the following process be employed in its production, the novel substance
resulting may be termed "thorium-zirconium silicated glass."
Upon subjecting the impregnated mantle to the heat of a gas-flame under
pressure, the component substances-namely, the thorium oxide, zirconium oxide,
silicic acid and alkali (partly as a carbonate)-being in a state of close com-
mixture, part of the alkali becomes volatilized, while the remaining part enters
into a reaction with the two acid components-that is to say, the silicic acid and the
zirconium oxide in the course of which reaction there forms a poor zirconium
silicic acid glass. With this glass, the thorium oxide combines in a secondary
stage.
In view of the necessity of operating with a flame subjected to an intensely high
pressure, it is necessary, in order to obtain a serviceable mantle, to proceed with

page_text: great caution to ensure an uniform calcination of the material. The well-known
action of cerium in Auer von Welsbach's incandescing bodies, and its capability
of forming enamels, suggested the idea that, where the last mentioned oxide is
present, the fusing process might be effected at a lower temperature and at the
same time rendered more equable. Actual tests proved the correctness of this
assumption; while they, at the same time, disclosed the fact that, if the cerium
oxide is to exercise no disturbing influence upon the process of formation, it must
be employed only in an accurately predetermined quantity. It was found that
the admissible and proper quantity of that oxide was limited to about 1 per cent.
of the amount of thorium employed; even slight additions to, or subtractions
from, that percentage producing a distorting effect upon the structure.
The mantle obtained is distinguishable from the generally known thorium-
cerium-mantle, not only by its density and elasticity, but by a characteristic
glass-like appearance, and also by the fact that the mantle tapers off towards the
top smoothly, that is to say, without any folds or wrinkles. Its 'illuminating
power is however inconsiderable; but inasmuch as it may be produced in the shape
of a very narrow-meshed network of thin filaments, it is admirably adapted for
use as a skeleton frame or support for other incandescing substances.
I
I have also found that, where cerium is present, the amount of thorium may be
very considerably in excess of 4 molecular weight-units without any fear of the
structure of the material, its firmness or density, its elasticity, or its permanency
as regards shape, being affected; provided always that the above mentioned pro-
portions of the thorium and cerium are carefully maintained. I have also found
that, in consequence of such an augmentation of the proportion of thorium and
cerium, the material acquires the power of emitting an intense white light. The
limit to which such augmentation of the proportions of thorium and cerium may
safely be carried is determined by the circumstance that, when a given maximum
is exceeded, the mantle would show an ever-increasing tendency to shrink at that
portion or zone which is exposed to the highest degree of heat. In practice, the
proportion of thorium may vary optionally. between 16 and 20 parts by molecular
weight. With these quantities, a beautifully formed firm elastic mantle of about
70 candle-power is obtainable.
r
From the diverse forms of thorium mantles which have hitherto been suggested
and which are claimed to have been improved by the employment of silicic acid,
this invention differs in a very marked manner by the fact of its producing a
thorium-zirconium-silicic-acid-glass, which is poor in alkali. It is further dis-
tinguishable by the unusual proportion in which the acid component occurs therein.
By the process described, a result has been successfully achieved which in itself
differentiates the present method from those that have been previously proposed,
viz., a mantle which, in spite of the presence of alkali and silicic acid, possesses
the properties of firmness and invariability of shape in a high degree; this result,
being attained in a manner calculated to ensure uniformity in the product, even
when manufactured'on a commercial scale.
Whether it be desired to produce a skeleton or an incandescent mantle, the
process, the subject of my present invention, may be performed in the following
manner:-
"T
Crystallized sodium silicate, so-called is dissolved in as much water as-is
necessary to produce, with the whole of the components, a solution containing
30 per cent. of the salt. The solution is mixed with as much nitric acid as is.
required to liberate the silicic acid which goes into solution. The remaining
ingredients of the mixture are then added in definite proportions, in the form of
nitrates, and so that neither the formation of a precipitate nor the clouding of
the liquid results. The fabric, in the production of which..allowance has been
made for shrinkage (about 50 per cent.) is now impregnated with this solution,
dried on the shaping-block, ignited, and fused or welded in a gas-flame under
pressure until it is found that the flame is no longer coloured by .the alkali.
The body, with 4 molecular weight-units of thorium, is now ready for use as a
1.4°

page_text: skeleton; while, if the proportion of thorium be higher, it may forthwith be
employed as an incandescing body.
It will be understood that the liquid for impregnating the mantle may if
desired, be prepared by mixing an aqueous solution of silicic acid with the metallic
ingredients in the form of nitrates or equivalent salts, as the case may be. Any
one of the series of metals of the earth alkalies may be employed.
. Skeleton foundations for mantles and incandescing mantles prepared in accord-
ance with the foregoing directions will be found somewhat more susceptible. to
the influence of low temperatures; tending, in fact, to become brittle in winter.
Moreover, after prolonged burning, and especially where the percentage of thorium
is comparatively high, there becomes observable, at the most intensely heated
zone, a slight concavity which, though not a serious drawback, detracts from the
technical perfection of the mantle. The applicant has found that both these
causes of disturbance may be effectually obviated by an addition of one of the
series of alkaline earths of the type R. O., which in order to enter the glass, will
displace part of the alkali Thorium may also be used; but an addition of
beryllium has proved to answer the purpose best. This addition should not, how-
ever, materially exceed 2 molecular. weight-units (calculated as oxide). Within
these limits, the bodies obtained will be found free from the defect of brittleness.
Also, this addition offers the great advantage of enabling a higher percentage of
thorium to be used; in fact, the amount of thorium may exceed 64 molecular
weight-units. The necessity for more forcible treatment with the gas-flame under
pressure, which would otherwise be entailed by such an addition, may be obviated
by a super-addition of boron in the form of boracic acid, or of borate of an alkali.
The amount of boron or borate added should, however, on no account exceed from
1 to 2 molecular weight-units.
Improvements in the Manufacture of Incandescing Media for Lighting
Purposes.
I, RUDOLF LANGHANS, of No. 6. Orn-der-Stadtbahn, Berlin, Prussia, German
Empire, late of No. 128, Elisabeth-Strasse, Berlin, Electrical Engineer, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed; to be particularly described and ascertained in and by the following
statement; -
This invention relates to improvements in the manufacture of incandeṣcing
media for lighting purposes, more particularly to the manufacture of mineral
structures, such as caps, mantles and the like, to be used on the Bunsen burner
for emitting light, by impregnating a combustible fibrous structure or skeleton
with a solution of suitable mineral salts, drying the impregnated skeleton, burning
the fibre, and exposing the mineral structure thus obtained to the action of an
intensely hot flame. The object of this invention is to so improve said manu-
facture that it results in a mineral structure or body in which permanency of
shape and mechanical strength when in the hot state shall be combined with a by
far higher degree of elasticity and resistance to shocks and jars when in the cold
state than hitherto met with in incandescent mantles and the like structures.

page_text: According to the present invention the said improvements are obtained by so
carrying out the process of producing the mineral structure that definite pro-
portions of thoria (thorium dioxide, Tho₂) and ceria (cerium dioxide CeO2) are
caused, by the agency of an alkaline metal oxide, to chemically combine, as basic
components, with definite proportions of silica (silicon dioxide, SiO2) and zirconia
(zirconium dioxide, ZrO2), as acid components whereby a compound is formed
which chemically speaking, has the nature of a glass, being a silico-zirconiate
of thorium combined with some ceria and alkaline metal oxide.
Moreover, the invention comprises means whereby the resistance of the structure
to the action of low temperatures which tend to render it brittle, is considerably
increased.
In order to obtain the best result the fluid for impregnating the fibrous structure
with such salts of the said components as are reducible to oxides by heat, should
contain the elements zirconiumi and silicon of the acid components zirconia and
silica in a quantity as close as possible to one molecular weight of each; the
quantity of thorium present, i.c. the element of the basic component thoria, may
be from at least four molecular weights up to twenty molecular weights, whereas
the quantity of cerium must be such that the proportion of ceria present in the
mixture of oxides left behind on burning the fibre is as close as possible to
one per cent. of the thoria present. As regards the alkaline metal oxide, it is
to be noticed that a small quantity suffices for causing the compound to be formed
but that a great proportion of it is volatilised in the calcining step.
With the fluid composed as described the manufacture results in a very regu-
larly shaped mantle having an evenly rounded head, which will stand the heat of
the Bunsen burner without shrinking or being distorted and has proved to possess
a considerable degree of elasticity in the cold state combined with a degree of
strength not hitherto found in incandescent mantles; moreover, the mantle or
otherwise shaped mineral structure looks like a vitrified mass by which appearance
it can readily be distinguished from any known description of incandescent bodies.
The result obtained is due to the fact that the constituents of the mantle or
other structure are not in the state of a mere mechanical intermixture or aggrega-
tion as is the case with the well known thoria-ceria mantle, but are bound together
chemically into a glass-like compound.
If
This may be explained as follows: When the impregnated and dried fabric is
burnt, the mineral structure left behind is composed of a molecular aggregation
of thoria (thorium dioxide, ThO₂) ceria (cerium dioxide, Ce0); alkaline metal
oxide, zirconia (zirconium dioxide, ZrO2), and silica (silicon dioxide, SiO2).
now the heat of a blue flame fed with gas under pressure is applied, part of the
alkaline metal oxide is volatilised, whilst another part combines with the
silica and zirconia, forming an alkaline zirconio-silicate poor in alkaline metal,
with this silicate the thoria and ceria combine in a second phase, the ceria acting,
moreover, somewhat as a flux.
"
The molecular proportions of the several components as above stated are those
which are preferred because they give the best result; in cases, however, where
perfect regularity of shape is of minor importance, the proportions of silicon and
zirconium may be slightly increased or diminished, and for this reason it is to
be understood, that the term one molecular weight" is intended to include such
slight variations. Besides considerably distorting the shape the effect of too
great a variation of the proportion of either one or of both of these components
is either to render the structure brittle in the cold state or to diminish its
resistance to the softening action of the Bunsen flame. As to the proportion of
ceria the more the same is increased or diminished the easier the mantle will
soften when used on the burner. The proportion of thorium should not be
greater than twenty molecular weights and not less than four molecular weights as
higher and lower proportions do not permit of obtaining the strength and elasticity
nor the regularity of shape which it is the object to impart to the mantle.
A structure, mantle or body so, composed as to contain four to eight molecular

page_text: weights of thorium will, though emitting light when used on the Bunsen burner,
not shown such a high illuminating power and agreeable colour of light as obtained
with bodies containing from eight to twenty molecular weights of thorium. Con-
sidering, however, the permanency of shape in the hot state of such low thoriated
bodies or mantles, their resistance in the cold state to shocks and jars, and the
fact that, owing to their glass-like nature, fabrics can be used that are made of
very fine threads, said low thoriated structures may be used with great advantage
as foundations or skeletons for supporting any desired special light emitting com-
position, with which they may be covered in the form of an adhering paste (for
instance prepared with a collodion solution), or by electrolytical deposition, the
structure being first covered with a fine layer of carbon, platinium or other suitable
conductors of electricity...
A structure, mantle or body containing from eight to twenty molecular weights
of thorium, when used on the Bunsen burner, will radiate a brilliant white light
and show a maximum illuminating power which is not inferior to that of the
wellknown thoria-ceria mantles, but is retained for a considerably longer period
of time.
In preparing the fluid it is preferred to proceed as follows: So called crystallis-
able sodium silicate is dissolved in so much water that after all of the other com-
pounds have been added, a liquor results which contains 30 per cent. of salts in
total and 70 per cent. of water. To this solution is added so much nitric acid as
is necessary for decomposing the sodium silicate, the silicic acid or silica liberated
thereby entering in solution as also the sodium nitrate formed. Then such salts
of thorium, zirconium and cerium as are reducible to oxides by the action of heat,
are added in the quantities necessary for causing their metallic elements to be
present in proportions as stated. It is preferred to use the nitrates of said earth
metals, especially the so-called basic nitrates of thorium and zirconium because
they are richer in oxides than the corresponding neutral compounds which are,
moreover, apt to do harm to the fibre owing to their acidity. The nitrates used
should be as free from iron as possible.. Instead of sodium silicate water-soluble
silicates of the other alkaline metals (potassium, lithium) may be used if desired.
Obviously the fluid may also be prepared by adding the nitrates of thorium,
cerium, zirconium and the alkaline metal to a watery solution of silicic acid.
The first way described is, however, preferred.
To serve as a guidance for those skilled in the art of making incandescent bodies
two examples for composing the fluid are given:
1. SKELETON (CONTAINING | MOLECULAR WEIGHTS of Thorium)
5,443 grammes of basic thorium nitrate (containing 48,5 per cent. of Tho₂).
0,690 gramme of basic zirconium nitrate (containing 44,27 per cent. of ZrO₂).
0,612 gramme of crystallisable sodium silicate (containing 48 per cent."of
water).
0,138 gramme of cerium nitrate (containing 38 per cent. of CeO₂).
2. INCANDESCENT MANTLE (CONTAINING 20 MOLECULAR WEIGHTS OF THORIUM).
6,804 grammes of basic thorium nitrate (containing 48,5 per cent. of Tho₂).
0,172 gramme of basic zirconium nitrate (containing 44,27 per cent. of ZrO2).
0,153 gramme of crystallisable sodium silicate (containing 48 per cent. of
water).
0,087 gramme of cerium nitrate (containing 38 per cent. of Ce0₂).
For making the structure or body, for instance a mantle, the usual fabric,
howing
.
5,443 grammes of basic thorium nitrate (containing 48,5 per cent. of Tho₂).
0,690 gramme of basic zirconium nitrate (containing 44,27 per cent. of ZrO₂).
0,612 gramme of crystallisable sodium silicate (containing 48 per cent. of
water).
0,138 gramme of cerium nitrate (containing 38 per cent. of CeO₂).
2. INCANDESCENT MANTLE (CONTAINING 20 MOLECULAR WEIGHTS OF THORIUM).
6,804 grammes of basic thorium nitrate (containing 48,5 per cent. of Tho₂).
0,172 gramme of basic zirconium nitrate (containing 44,27 per cent. of ZrO2).
0,153 gramme of crystallisable sodium silicate (containing 48 per cent. of
water).
0,087 gramme of cerium nitrate (containing 38 per cent. of CeO₂).
For making the structure or body, for instance a mantle, the usual fabric,
having, for sons hereinafter stated, twice the length and width of the mantie
to be produced, and meshes of double the width as compared with those of the
fabric generally used, is impregnated with the fluid prepared as described; the im-
pregnated fabric is placed on a mould and dried, when it is removed from the
mould, and the fibre burnt, all as well known to those skilled in the art; finally,
the mineral structure left behind is exposed to the action of a blue gas flame which

page_text: is fed with gas under pressure. Under the action of this flame, a shrinking of the
structure takes place amounting to fifty per cent. of the volume of the moulded and
dried fabric. This calcining process is continued until the flame ceases to show
the yellowish colour imparted to it by the vapours of the volatilised sodium, when
the structure is ready for use either as a skeleton or as an incandescent mantle
according to the proportion of thorium contained therein.
Skeletons and incandescent mantles produced as described manifest a tendency to
become brittle under the action of low temperatures so that very cold winter days
might be fatal for them. This defectuosity can be perfectly removed by adding,
on preparing the fluid, a salt reducible to oxide under the action of heat, of an
alkaline earth metal of the series RO, or of thallium. In any case it is preferred
to use a beryllium compound, such as beryllium nitrate, beryllium chloride, or
basic carbonate of beryllium. The proportion present of such earth alkaline metal
should not, however, be higher than two molecular weights. When the mineral
structure obtained by burning the impregnated fabric, is acted upon with the
calcining flame, the glass-like compound as specified in the preceeding part of
this specification is first formed, when the oxide of the alkaline earth metal,
possessing a higher resistance to heat than the alkaline metal oxide enters into
the composition of the said compound by substituting part of the sodium oxide.
The presence of the alkaline earth metal oxide makes it necessary to apply a
higher pressure in feeding the calcining flame with gas. This may in some
extent be avoided by adding to the fluid boric acid or a borate of an alkaline
metal, preferably sodium borate, which, as is well known, will be come active
as a flux in the calcining step. The proportion of boron thus introduced in the
structure must not, however, be more than two molecular weights for the reason
that the increased fluxing power of higher proportions does not allow sufficiently
refractory structures to be obtained.
In the examples given above if beryllium oxide is desired to be combined with
the silico-zirconiate of thorium, 0,489 gramme of beryllium nitrate (containing
13 to 14 per cent. of beryllium oxide) and 0,380 gramme of boric acid may be used
for the skeleton (1st exaniple), and 0,164 gramme of beryllium nitrate (containing
13 to 14 per cent. of beryllium oxide) and 0,108 gramme of boric acid for the
incandescent mantle (2nd example).
Besides making the structure better withstand the cold, the presence of beryllium
oxide allows the proportion of thoria to be increased up to a quantity correspond-
ing to 128 molecular weights of thorium without in the least injuring the elasticity,
strength, permanency of shape and light emitting power of the mantle, provided
the proportion of cerium be simultaneously increased accordingly, that is to say
so that in any case the proportion of ceria present in the mixture of oxides left
behind on burning the fibre is as close as possible to one per cent. of the thoria
present.
The following example may serve as a guide for producing such highly thoriated
incandescent mantles.
3. INCANDESCENT MANTLE HAVING 64 MOLECULAR WEIGHTS OF THORIUM:
15,240 grammes of basic thorium nitrate (containing 48,5 per cent. of Tho₂).
0,110 gramme of basic zirconium nitrate (containing 48,46 per cent. of ZrO2).
0,107 gramme of crystallisable sodium silicate (containing 48 per cent. of
water.
0,196 gramm of cerium nitrate (containing 38 per cent. of CeO₂).
0,164 gramme of beryllium nitrate (containing 13 to 14 per cent. of oxide).
0,064 gramine of boric acid.
I am aware that attempts have been made to strengthen incandescent mantles
by the aid of silicic acid, but never, as far as I know, has this substance been
used in combination with zirconia as a second acid component for forming a
ceriated glass-like compound with thoria, and no man has discovered prior to me
that the use of said substances in proportions as stated has the effect of giving the

page_text: structures formed with them a high degree of elasticity and strength in the cold.
state and permanency of shape in the hot state without damaging but improving
the light as well as the constancy of maximum illuminating power.
Having now particularly described and ascertained the nature of said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:-
1. The herein before described improvement in the manufacture of mineral.
structures for use with incandescent burners as the incandescent bodies thereof or.
as the skeletons or foundations of such bodies by impregnating a combustible.
fibrous structure with a fluid, being a solution of suitable mineral salts, drying.
the impregnated fibrous structure, burning the fibre, and exposing the mineral
structure left behind to the action of an intensely hot flame, which consists in
impregnating the fibrous structure with a fluid prepared from compounds reduc-
ible to oxides by the action of heat, such as nitrates of thorium, an alkaline metal
and zirconium together with silicic acid and a cerium compound such as cerium
nitrate, in such quantitative relation that the elements silicon and zirconium are.
present, each in the proportion of one molecular weight or slightly more or less,
and the element thorium in the proportion of at least eight molecular weights for
the incandescent body, and of at least four molecular weights for the skeleton, the
proportion of cerium being such that the amount of ceria present in the mineral
structure left behind on burning the fibre will, not he materially greater than one
per cent. of the thoria then present, substantially as and for the purpose stated.
2. A modification of the improved manufacture as specified in the First Claim
which consists in adding to the fluid specified in the First Claim a compound
reducible to oxide by the action of heat, of an alkaline earth metal of the.
type RO or of thallium, particularly compounds of beryllium, the proportion of.
alkaline earth metal or thallium introduced by such addition being not materially
greater than two molecular weights, substantially as and for the purpose stated.
3. The products manufactured according to the 1st Claim.
4. The products manufactured according to the 2nd Claim.
RUDOLF LANGHANS.