1010

THE COLLIERY GUARDIAN.

November 24, 1916.

CURRENT SCIENCE

The Texture of Firebricks.

In a paper read before the Faraday Society, Dr. J. W.
Mellor said the requirements from firebricks vary so
widely in different furnaces, or in particular parts of a
single furnace, that the ideal firebrick can be defined
only in abstract terms, and this the more because some
properties of firebricks are antagonistic in the sense
that some characteristics can be highly developed only
at the expense of others. The manufacturer who seeks
to develop particular qualities in his bricks, especially
fitted for particular purposes, is often handicapped by
competition against bricks made possibly with good
refractory clays, but in which no attempt has been
made to control the product.

Texture is one of the most important qualities of a
firebrick, since the life and character of a firebrick are
largely determined by its texture. The texture of a
refractory may vary from that of the light porous
bodies used in making bricks for insulating boilers, etc.,
to non-porous or vitreous bodies used in making
crucibles, acid-resisting bricks for acid towers, etc., and
there are quite a number of intermediate types.

The more important mineral constituents of clays are
the granular felspathic or micaceous fluxes, granules of
clay proper, and quartz grains. Virtually all fireclays
may be considered to have been made by Nature by
mixing these three components with what might be
called accidental—often deleterious—impurities : -schorl,
pyrites, siderite, etc.

When the clay is burnt in the kilns, the fluxes begin
to melt at about 900 degs. or 1,000 degs , and they begin
to attack the surfaces of the clays and quartz grains.
At a still higher temperature the granules of clay and
quartz which are in contact also begin to react, so that
clay is a high temperature flux for quartz (or silica),
and quartz (or silica) is a high temperature flux for
clay. With silica and ganister bricks, either clay or
lime, or both, are the fluxes. The fluxing action, of
course, is necessary to bind the brick into a compact
whole, to give the brick a high crushing and tensile
strength, and to give the brick the power of resisting
abrasion and attack by flue dust, slags, etc. This
fluxing or vitrification is a time reaction—it is relatively
slow at low temperatures and fast at high temperatures ;
a long-protracted fire at a low temperature can produce
virtually the same contraction as a shorter fire at a
higher temperature.

There is an enormous increase in the number of
granules for a given mass of clay as the dimen-
sions of the particles are reduced. Thus, reducing
the diameter of the grains from 1 to 0*0001 mm.
diameter raises the surface area of the grains from
22*6 sq. cm. to 226,415 sq. cm. Consequently, if the
vitrification of a clay is the result of a reaction between
the surfaces of contact of the granules, the speed of
vitrification must be increased when the area of the
surfaces in contact with one another is augmented. It
follows also that pressure might be expected to lower
the softening temperature of a clay by bringing the
surfaces of the granules into more intimate contact.
Observations on this phenomenon have showed that with
clays of approximately the same grain size, the softening
temperature is reduced by pressure in accord with the
exponential law—

Squatting temperature = Ce — kP,
where C denotes the squatting temperature of the clay
under no load, P denotes the pressure in lb. per square
inch, and k is a constant of the order 0 0001, but which
has in general smaller values for siliceous than for
aluminous clays.

Anything which favours the vitrification of a clay
reduces its refractoriness or fire-resisting qualities.
Consequently, other things being equal, the coarser the
grain of a clay the higher its softening temperature,
and the coarser the texture, the more refractory the
brick. This is very noticeable with high-temperature
fluxes like mixtures of clay and fine-grained quartz,
where the temperature of vitrification may be so reduced
that the admixture spoils the firebrick. On the contrary,
if the quartzose silica be coarse-grained, the refractori-
ness may appear to be improved. Firebricks made with
some clays, with or without fine-grained silica, break
down at temperatures which they withstand when made
from the same clay mixed with coarse-grained quartz.

The quartz grains should be angular, and not in the
form of rounded pebbles. The angular grains are
firmly embedded in the clay matrix, while the rounded
grains are loosely held by the clay bind and are easily
picked out. Again, angular fragments pack together
more closely and form a more compact skeleton for the
brick than rounded grains. Moreover, when clays are
heated on a gradually rising temperature the surfaces
of the more fusible granules melt first. Hence again,
quite independent of the action of the fluxes, a fine-
grained clay with its augmented internal surface will
vitrify faster and at a lower temperature than a coarser
grained clay of the same composition. There is there-
fore a cumulative action in favour of coarse-grainedness
for highly refractory bricks.

The speaker also dealt with after-contraction and
after-expansion; grog; machine v. hand-made fire-
bricks ; chemical analysis ; and coarse — and fine-
grained firebricks; and concluded with the following
remarks:—“We are all aware of the difficulty in
laying down general rules with respect to clays,
since, taken individually, clays from different deposits
have a remarkably varied character. In spite of this,
I felt that probably more good would obtain if
I opened this discussion by trying to show that the
texture of a firebrick is virtually as important as
refractoriness and chemical composition. The texture
can be largely controlled by the manufacturer. The
consumer has to carefully consider the conditions which

AND TECHNOLOGY.

prevail in different parts of any particular furnace
before he selects for trial particular types of firebrick as
likely to suit particular parts of his furnace. The
bricks near the top of the furnace are not exposed to
high temperatures, but there they have to withstand a
certain amount of abrasion, impact and change of
temperature. The bricks are liable to spalling and
disintegration, due, as is supposed, to the deposition of
carbon formed by reactions between the iron oxide in
the brick and the furnace gases. Nodules or patches of
iron oxide in the bricks are more liable to serious
trouble than is the case when the iron oxide is more
uniformly diffused throughout the mass, possibly
because, in the latter case, the iron oxides are
fixed by the alumino-silicates of the brick, and
they then resist better the action of the furnace
gases. The bricks should also be close and compact;
such bricks are usually tough and are not so permeable
to gases. The temperature conditions become increas-
ingly severe in descending the furnace. The upper
parts of the lining are normally protected to some
extent by the development of a surface film of carbon,
but the friction of the descending charge and the
impact of fine particles of solid carried forward by the
blast may produce erosion, particularly if concentrated
in local parts. The bricks in the mid zone are also
exposed to the slagging effects of particle$*of salt and
other basic fluxes from the coke. There are no very
abrupt temperature changes, so that a close-textured
compact brick is desirable for this region. The condi-
tions which prevail in the hearth and bosh require a very
special brick to withstand high temperature, to resist
the scouring action of highly basic molten slag, and a
rather heavy mechanical load; the volume changes
should be small, since the bricks must be tight without
leakage; but there is comparatively little wear and tear
by abrasion. The stove bricks should have a high
thermal capacity, so that they can absorb and give up
the largest possible amounts of heat and be capable of
resisting the sand-blasting action of flue dust. I do not
know if the former quality can be controlled by
the manufacturer, although the remarkable rise in
the specific heat of firebricks with temperature is
worthy of note. It will, however, be clear that the
mechanical resistance of a firebrick to the cutting action
of swift streams of flue dust can be to some extent con-
trolled by the manufacturer. The chemical resistance
of a firebrick to types of flue dust is largely determined
by the chemical composition of the firebrick. For
instance, other things being equal, ferruginous coal
ashes in a stream of burning producer gas will have
a more severe action on siliceous than on aluminous
bricks.”

Harnessing a Volcano for Power Production.

The idea of utilising volcanic heat to drive an
important electric power-house of 15,000 h.p. might
have been considered Utopian in ordinary conditions.
It has, however, become a reality now that the price of
coal in Italy has reached £8 to £9 a ton in the harbours
and £9 to £10 in inland towns. As reported in
Engineering, the installation had this origin : In Central
Tuscany, near Volterra, there are numerous cracks in
the ground, from which powerful jets of very hot steam
spout high in the air with great violence and constancy,
bringing up boric acid—which is very valuable—and
other mineral substances of less importance. These
powerful jets of superheated steam are called soffioni
—the “ blowers ”—and have been utilised for many years
in the production of boric acid and borax, and
occasionally for warming the houses in the village of
Larderello. The larger proportion of the steam, how-
ever, is lost, having no local application, and with it is
lost its very valuable heat Prince Gin ori-Conti, the
president of the ‘‘ Societa Boracifera di Larderello,” was
the first, in 1903, to try to utilise this superheated steam
for the production of motive power. At fir.>t he applied
a strong jet to a small lotary motor, then to a very
modest reciprocating steam engine connected to a
dynamo, which generated sufficient current to light part
of the borax works. In the meantime he tried to get a
more ample supply of steam by boring holes in the
ground, lined with iron pipes, driven down to the very
source of the steam, which is under a hard stratum of
rock about 300 to 500 ft. below the surface. These
boreholes vary from 12 to 20 in. in diameter, and give
forth steam with a pressure from 2 to 3, and excep-
tionally np to 5. atmospheres, and at temperatures
varying from 150 to 190 degs. Cent. For several
years these jets have not diminished in their capacity,
nor does a new boring seem to interfere with the pre-
ceding ones, provided the distance from one to another
is not less than 50 ft. Experiments have demonstrated
that each bore can provide steam at a temperature of at
least 150 degs. Cent., and from 15,000 to 25,000 kg.
per hour, that is, practically, from about 1,000 to 2,000
theoretical horse-power per hour. Encouraged by these
results, Prince Ginori-Conti, in 1906, applied the steam
to an ordinary steam engine of about 40 h.p. The
experience of several years has shown that this arrange-
ment works well so far as the mechanical power of the
steam is concerned, but that the borax salts and the
gases mixed with the steam—especially sulphuretted
hydrogen and traces of sulphuric acid—have a corrosive
action on the iron parts of the engine and are the cause
of frequent repairs. This difficulty was avoided by
applying the superheated steam not directly in the
engine, but to a boiler; that is, by applying it instead
of fuel to an ordinary multitubular boiler, in which steam
was produced at a pressure of 2 atmospheres, then
passed through a superheater, and afterwards used for
driving a 300-h.p. condensing steam turbine, directly
connected with a tri-phase electric generator, which
supplies the works and the villages around Larderello.

This installation had been at work successfully for
several months when the war broke out. Then, coal
becoming very scarce, and prices rising up to prohibitive
limits, the possibility of using on a large scale this
natural steam became very important. Prince Ginori-
Conti carried out trials on a large scale, availing him-
seb of his long and successful experiments ; and, on the
advice of the Tosi Works, of Legnano—he ordered three
groups of condensing turbo-electric engines, each of
3,000 kw., working with super-heated steam at atmo-
spheres, generated in especially-constructed multi tubular
boilers, the latter arranged vertically and with
aluminium tubes, both for greater utilisation of the heat
and better resistance to the corrosive action of the
natural steam from the soffioni.

THE GERMAN COAL AND IRON
TRADES.

We give below further extracts from German
periodicals that have reached us, showing the course of
the cofil and iron trades in Germany :—

German Pig Iron Output in September.

Of a total output of 1,116,752 tons in September
(1,034,124 tons in September 1915), 169,102 tons were
foundry pig; 11,302 tons acid Bessemer pig; 725,142
tons basic Bessemer pig; 195,744 tons steel-iron and
spiegeleisen; and 15,462 tons puddling pig. Of the
various producing centres, Rhenish Westphalia turned
out 473,577 tons (462,393 tons); Siegerland, Hesse-
Nassau and Wetzlar, 71,975 tons (66,115 tons); Silesia,
60,637 tons (64,559 tons); Mid Germany, 34,875 tons
(32,261 tons); North Germany, 21,091 tons (20,262 tons);
South Germany and Thuringia, 22,241 tons (18,658
tons); Saar district, 85,870 tons (69,418 tons);
Lothringen, 184,068 tons (160,259 tons); Luxemburg,
162,418 tons (140,199 tons).

Fuel Traffic in Ruhr Harbours During September.

The shipments to Coblenz and places higher up
river amounted to 406,580 tons (561,282 tons in Septem-
ber 1915); to places below Coblenz, 26,998 tons (18,274
tons); to Holland, 100,851 tons (139,459 tons); to
Belgium, 22,101 tons (45,738 tons) ; to other destina-
tions, 21,898 tons (9,699 tons). The total shipments
from the various ports were:—Duisburg-Ruhrort,
431,872 tons (618,995 tons); Rheinpreussen. 74,148 tons
(66,739 tons); Schwelgern, 11,492 tons (25,173 tons);
Walsum, 60,914 tons (63,544 tons), an aggregate of
578,427 tons (774,451 tons) or a decrease of 196,024 tons.

Renewal of the Coal Syndicate.

As already announced, the Westphalian Coal Syndicate
has been renewed for a period of five years, dating
from April 1 next. The number of members has been
increased to 93, chief among them being the following
(with a participation of 1,000,000 tons of coal and
upwards):—Arenbergsche A.G., 2,243,300 tons (and
687,250 tons of coke); Augusta Viktoria, 1,000,000 tons
(and 325,000 tons of coke); Concordia, 1,200,000 tons
(and 100,000 tons of coke); Consolidation, 1,951,800 tons
(and 515,400 tons of coke); Constantia der Grosse,
2,762,800 tons (and 1,200,200 tons of coke); Dahlbusch,
1,210,000 tons (and 183,000 tons of coke); Deutscher
Kaiser, 1,650,000 tons (and 35,000 tons of coke) ;
Deutsch-Luxemburg A.G., 3,635,000 tons (and 853,600
tons of coke); Emscher Lippe, 1,150,000 tons (and coke
increasing up to 1,100,000 tons); Essener Bergwerks-
verein Kbnig Wilhelm, 1,138,100 tons (and 543,367 tons
of coke); Essener Steinkohlenbergwerke, 2,325,900 tons;
Ewald, 2,449,000 tons (and 300,000 tons of coke); Fried-
rich der Grosse, 1,189,900 tons (and 506,500 tons of
coke); Friedrich Heinrich, 1,200,000 tons (and 450,000
tons of coke); Gelsenkirchener Bergwerks A.G.,

9.995.700	tons (and (1,826,808 tons of coke); Graf
Bismarck, 2,326,600 tons (and 300,000 tons of coke);
Gutehoffnungshiitte A.V., 2,116,600 tons (and 40,000
tons of coke); Harpener Bergbau AG., 7,788,800
tons (and 2,050.000 tons of coke); Helen and Amelia,
1,015,000 tons (and 357,800 tons of coke) ; Hibernia,
5,813,500 tons (and 1,512,000 tons of coke); Koln-
Neuessener B.V.. 1,971,800 tons (and 553,540 tons
of coke) ; Kgl. Bergwerks direction Reckling-
hausen, 5,000,000 tons, to be increased progressively to
6,815,000 tons in 1921 (and 2,000,000 tons of coke);
Kbnig Ludwig, 1,434,300 tons (and 593,050 tons of coke);
Konigsborn, 1,124,800 tons (and 413,900 tons of coke);
Lothringen, 1,214,800 tons (and 545,000 tons of coke);
Loth ringer H.V. Aumetz-Friede, 1,905,300 tons (and
331,940 tons of coke); Mannesmannrohren-Werke,
1,300,000 tons (and 400.000 tons of coke); Mathias
Stinnes, 1,729,000 tons (and 248.195 tons of coke) ;
Mulheimer B.V., 1,380,000 tons (and 95,000 tons of
coke); Neumuhl, 1,650,000 tons (and 563,000 tons of
coke): Phbnix, 3,190,000 tons (and 742,640 tons of coke);
Rheinpreussen, 3 million tons (and 795,000 tons of
coke); Trier III., 1,200,000 tons (and 410,000 tons of
coke) ; Zollverein, 1,950,200 tons (and 540.000 tons
of coke). In addition, a number of firms have received
allotments, to raise coal for their own consumption in
iron works, the largest being :—Bochumer Verein,
792,400 tons; Concordia, 700,000 tons (increasing to
1 million tons in 1920); Deutscher Kaiser, 2,723,000
tons; Deutsch-Luxemburg A.G., 2,021,300 tons ; Eisen
und Stahlwerk Hoesch, 905,400 tons; Fried. Krupp,

2.992.700	tons; Gelsenkirchener A.G., 2,085,000 tons;
Gutehoffnungshutte AV., 1.635,200 tons ; Loth ringer
A.V. Aumetz-Friede, 1,040,200 tons; Minister Achen-
bach, 900,000 tons; Phbnix, 2,473,400 tons; and
Rheinische Stahlwerke, 1,100,200 tons.

As in the interim Syndicate, the Prussian State is
represented by the Minister of Commerce and Industry,
who retains the right to dispose of 450,000 tons of coal
(in addition to the participation allotted to the State
Collieries) for the public service; and this figure may