Index Home About Blog
From: "donald haarmann" <>
Subject: Re: thoria
Date: 11 Oct 1999
Newsgroups: sci.chem

BillyFish <> wrote in message

> I do not believe this to be true.  Thoria is practically transparent
> even at high temperatures.  (High Debye temperature) Thermal radiation,
> therefore, is much smaller than for black bodies.  Mantles are made by
> ading ceria to the thoria, thereby providing absorption bands and
> incandescant radiation as a slective radiator.
> Bill

From one of my favorite books:
Edward Thorpe's - A Dictionary of Applied Chemistry 1913

Industrial application of Thoria v. GAS MANTLES. Gas mantles are
generally woven in cotton or preferably ramie fibre, but artificial silk
has also been employed, and formerly the thorium-cerium. solution was
added to the dissolved cellulose before it was spun into thread. The
present practice, however, is to impregnate the woven stocking just as in
the case of ramie or cotton fibre. The rare earth nitrates may be
replaced by 'the corresponding acetates or formates and, with artificial
silk, the impregnated stocking is treated with ammonia or some volatile
alkali such as hydrazine or tetraethyl- ammonium hydroxide in order to
produce within the fibres the hydroxides of thorium and cerium. Hydrogen
peroxide may also be employed as the precipitant. In either case, the
stockings are washed free from soluble salts (ammonium nitrate, &c.) or
acid; the head is hardened with a solution of magnesium, aluminium,
zirconium, glucinurn or chromium salt, and the mantle 'burnt off' and
'seasoned' as in the case of the ramie fibre.

Although in most instances the optimum effect is attained by mixing the
thorium and cerium salts in such proportions that the mixed oxides of the
mantle consist of 99-0 p.c.  of thoria and 1-O p.c of ceria, yet owing to
the yellow colour of the light produced by this amount of ceria in
inverted mantles using high-pressure gas, it is customary in this form of
illumination to reduce the proportion of ceria to 0-5 p.c.

A pure thoria mantle gives no emission in the visible region of the
spectrum and only a slight radiation of infra-red rays of short wave
length. A cerium dioxide mantle gives a maximum radiation at the extreme
red end of the visible spectrum, the intensity at first diminishes in the
infra-red region and then increases again for heat rays of longer wave
length. In this mantle there is, on the whole, a relatively considerable
loss of heat by radiation, the temperature remains comparatively low and
consequently the emission of light rays is only feeble.

In the Welsbach mantle containing 0-5 p.c. to 1-5 p.c. cerium dioxide,
the emission of light is selective and attains its maximum in the blue
region of the spectrum. On the other hand, the heat radiation is
remarkably small, except for rays of comparatively long wave length.
Consequently the temperature attained by the mantle is comparable with
that of the flame itself. The cerium dioxide colours the transparent
ground mass of thoria so that an intense selective absorption is
developed in the visible region of the spectrum and, providing that the
amount of colouring oxide is small, this result is attained without any
appreciable increase in the loss of heat by radiation and consequently
without diminution in the intensity of illumination.

One hundred parts of thoria can hold in solid solution 6-7 parts of
cerium dioxide, and as the mantle contains only about 1 p.c. of the
latter oxide, it is entirely in the dissolved condition. Owing to this
intimate mingling of the two oxides, a very small addition of cerium
dioxide suffices to bring about the intense emission of light waves
whilst the increase in heat radiation is too slight to act injuriously.
If, however, the proportion of cerium is raised, the greater loss of heat
by radiation leads to lowering of the mantle temperature and consequent
diminution in luminosity. Cerium dioxide itself is stable in the Bunsen
flame, but nevertheless the ignited mixed oxides, when treated with
hydrochloric acid and potassium iodide solution liberate an amount of
iodine corresponding with only a portion of the dioxide originally
introduced into the mixture.  This result suggests the possibility of
some chemical combination between the cerium and thorium oxides which may
be the chemical cause of the characteristic physical properties of the
Welsbach gas-mantle (cf. White and Traver, J. Sec. Chem. Ind. 1902, 21,
1012 ; Lewes, Chem. News, 1905, 26, 62 Journ. Gas Belcuchtigung, 1903,
46, 787, 974 R. J. Meyer and Anschiltz, Ber. 1907, 40, 2639).



Seldom in the industrial history of the world has any one invention
wrought such alterations in a great manufacture as has been the case with
the incandescent mantle, which, being perfected just at the time when
electricity was threatening the supremacy of gas as an illuminant,
entirely revolutionized the gas industry.

Before the introduction of the mantle, the usual quality of the gas
supplied was what was known as 16-candle power, and the light obtained
"from it by the consumer was anything from 7 to 8 candles per cub. ft.
with regenerative burners, down to less than 1 candle per cub. ft. ,with
small flat-flame burners, whilst with the incandescent mantle from 14 to
35 candles per cub. ft. can be obtained.

It was also soon found that, in practice, a much poorer gas gave as good
or better results with most incandescent mantle burners, and with the
general adoption of the mantle, the candle power of the gas supply has
been lowered in nearly every large town in England.

At the present time (1912), the annual mantle consumption of the world
approximates to:

England  38 000 000 mantles
America  60 000 000
Germany 100 000 000
France  16 000 000
Italy  3 000 000
Belgium 3 500 000
Russia  1,500,000

When Welsbach made the first thoria mantles, thorium salts were
obtainable only in very small quantities, and from such minerals as
thorite and orangite, but with the demand, new sources of supply were
found in many directions, and during the last few years, although the
amount of thorium nitrate used has more than doubled, the price has
fallen by one half, and there appears no fear of a shortage hampering the
mantle industry.

Many theories have been brought forward to explain the wonderful
light-giving power of the mixture of 99 p.c. thoria, and I p.c. ceria,
but none of them explains both the two facts, i.e. that the maximum light
is obtained only in the extreme outer layer of the Bunsen flame, where
both air and combustible gases are present, and that it is only with 1
p.c. of ceria in the mixture that it is obtained, a mantle of pure thoria
or pure ceria giving practically no light.

The probable explanation is that in the mantle, the thoria, being in a
porous condition, is a good non-conductor, and owing to this, to its low
specific heat and low power of radiating heat, it can be raised to the
temperature of the flame; ceria, on the other hand, has a wonderful power
of radiation, as shown by Fèry, and has also a catalytic action upon
mixtures of combustible gases and oxygen, but its radiation is so great
that it cannot be heated in a Bunsen flame to the temperature necessary
to give light.

When ceria is added to thoria, the light emitted by the mantle increases
until I p.c. by weight, or 0-1 p.c. by volume, is present, because the
ceria is so insulated by the excess of thoria that it is not only brought
up to the temperature of the flame, but by its catalytic power tends to
focus the combustion of the extremely attenuated flame gases upon the
widely distributed ceria particles, and so raises them to a far higher
temperature than the mantle, a temperature, however, which cannot be
detected by the thermo-couple, which gives only the average temperature
of the mass with which it is in contact, and fails to show the
temperature of the 0-1 p.c. of ceria. Addition of more ceria to the
mixture causes such a rapid cooling of both mantle and flame by
radiation, that tight at once begins to fall; and by the time 10 p.c. of
ceria is in the mixture, the mantle gives no more light than a thoria
mantle, but a much increased heat radiation.

The work of Le Chatelier, Nernst, Schmidt, and others, shows that the
thoria-ceria mixture gives light rays rich in blue, green, and yellow,
but poor in red, so that the proportion of energy

donald j haarmann - colophon

Index Home About Blog