Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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The following comparison of British, Continental, and American
soke, is based on the returns for 1889 and 1890 :—

British: 1*65 tons of coal make 1 ton of coke, costing 7«. 11^.
per ton of 2000 lb., of which the coal amoimts to 5ff. llfi. or 74**63
per cent., and the labour to 1«. 4^ or 17*24 per cent.

Continental : 1 * 327 tons of ooaI make 1 ton of coke, costing 9«. 6(2.
per ton of 2000 lb., of which the coal amounts to 8«. 5(1. or 89*28 per
oeat, and the labour to 9^ or 8*4 per cent.

American: 1 *555 tons of coal make 1 ton of coke, costing 6«. lid.
pa- ton of 2000 lb., of which the coal amounts to h%. 0^ or 73 per
oenU, and the labour to 1«. 5^. or 21 • 1 per cent.



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2i8 ECONOMIC MINING,



EMERY AND CORUNDUM.

While emery and comndnm are very nearly allied mineralogicallj
they are sharply distinguished in the trade. Whereas oomndnm is
almost a pnre aJnmina, emery is contaminated by a large proportion
of iron oxide, ranging generally between 20 and 33 per cent
Physically also they are distinguished by the following features:—
Corundum is variously coloured, commonly grey, but never black ; it
is much harder than emery, with sharper edges, and cats more deeply
and rapidl}- ; it is, however, more brittle and therefore less durable.
Emery is practically always black.'

The chief European sources of emery are the Greek island of Naxos
and Asiatic Turkey.

The Naxos deposits occur chiefly near Bothis at the northern end
of the island, which is principally made up of metamorphio rocks,
divisible into gneiss and schist formations, the latter consisting of
mica schists alternating with crystalline limestones. The lenticular
masses of emery, which are very variable in size, ranging in length
from a few feet to upwards of 100 yd., and in thickness frum 5 up to
50 yd., are closely associated with the limestones, and follow tneiT
undulations ; they vary much in position, lying at all angles, from
horizontal to nearly vertical. The highest quality of tuineral is
obtained from two comparatively thin, but extensive deposits,
Aspalanthropo and Eakoryakos, which are 435 m. above the sea-level
The mineral is stratified in thin bands 1-2 ft. thick, crossed by two
other systems of divisional planes, so that it breaks into nearly
cubical blocks in the working. The floor of the deposit is invariablj
crystalline limestone, and the roof a loosely crystalline dolomite
covered by mica schist. The underlying limestones are often pene-
tmted by dykes of tourmaline granite, which probably have some
intimate connection with the origin of the emery beds above them.
The working of the deposits is conducted in an extremely primitive
fashion by about 600 privileged woikmen, who have the right of
working the mineral wherever and in what manner they think bett.
The produce is taken over by the Government oflficial at the mte of
about U. 6(i. per cwt^ The rock is exclusively broken by fire-setting.
A piece of ground about 5 ft. broad and the same height, is cleared
from loose material, and a pile of brushwood is heaped against it and
lighted. This bums out in about 24-30 hours, when water i«
thrown upon the heated rock to chill it and develop fractures alon^
the Hecondary divisional planes in the mass of emery, and so facilitate
the breaking up and removal of the material: Sometimes a crack if
opened out by inserting a dynamite cartridge, but the regular use ol
explosives is impossible, owing to the hardness of the mineral, wbiek
cannot be bored with steel tools. Only the larger lumps are carrM
down to the shipping place, the smaller, up to pieces as large as tfce



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NON-METALLIFEROUS MINERALS. 219

Bat, being left on tlie ground. Ab most of the suitable places for
Ere-setting at the surface have been worked out, attempts have been
made to follow the deposits underground, but none has been carried
to any depth, partly on account of the suffocating smoke of the fires^
rendering continuous work difficult, but more particularly from the
langerous character of the loose dolomite roof, which is responsible
for many fatal accidents from falls. These might, of course, be
prevented by the judicious use of timber or masonry to support the
roof; but this appears to be beyond the skill of the native miners, and
the rapid exhaustion of the forests in the neighbourhood of the mines
owing to the heavy consumption of fuel in fire-setting, has been a
cause of anxiety to the Qovemment for some years past.

Emery stone is found in nearly all parts of Asia Minor, and not
imfi:eqnently in the remote and almost inaccessible regions of the
interior, where the natural obstacles are too great to offer any induce-
ment to the miner. The principal mines are confined to the districts
of Thyra and Aidin, situated to the southward of Smyrna. When well
lacked and freed from unsound ore and rubbish, the emery from the
Chamaud, Jackson, and Abbot mines is of good and nearly equal
quality. The Glyka or Akdere stone is not as much sought after,
while that excavated near Milassa, the larger part of which finds pur-
ebasers in the United States, is of inferior quality, the grain being
Rnooth and a great deal of magnetic iron entering into its composition.
The mines are opened by pits and galleries, and the stone is obtained
in most instances by blasting, gunpowder and dynamite being fn^ly
w>ed to extract it. The overseers and principal workmen at the mines
are Italians, who are paid d«. 6(2. per diem ; the native workmen are
paid only about half as much. In some cases the mining is attended
with difficulty and expense. At the Jackson mine, for example, the
•(one is procured from a great depth, water neoesHitating the employ-
ment of a steam-pump. At Kourchak not even blasting is required,
the emery being dug up from the red argillaceous earth wherewith it
ia mixed. The coating of the stone varies with the colour of the earth
or rock in which it is found — from red to brown, grey, or white ; and
as a rule no correct judgment of the quality can be formed from its
outward appearance. The grain should be hard, bright, and coarse,
r^embling gunpowder, and varying in hue from reddish black to dark
blmsb grey. The grain must be tested before one can certainly know
its abrasive power, which does not solely depend upon the amount of
tlumina it contains, but also upon the molecular construction. In the
Tchaous concession, near Thyra, a great deal of the emery is not mined,
owing to the presence of mica in the grain. The emery is picked
dailv at the mines as fast as it is extracted, in some instances not one-
ball the quantity being selected. It is then conveyed by camels to
the nearest railway station, and from thence to Smyrna, where it is
generally picked again previous to shipment. When the mines are
litnated on heights inaccessible to camels, the ore is brought down by
donkeys. If the pieces are too large to be carried by camels, they are
brought to the station in carts drawn by buffaloes. But these very
Urge pieces are broken at the mines with sledge-hammers, after having
been subjected to the action of fire to facilitate their breaking.

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220 ECONOMIC MINING.

Gorundnm has been found in a large number of localities in tho
United States, but only three places have been actual producers. The
emery vein or bed at Chester, Mass., has furnished a large quantity of
the mineral ; but the chief American source at present is a belt of ser-
pentine that extends from south-western North Carolina into Georgia.
It is an altered olivine rock, and has gneiss for its immediate associate,
and along the contact of the two are found the veins (or beds) of de-
composed rock which have the corundum disseminated through them.
Corundum Hill, in North Carolina, and Laurel Creek, in Georgia, are
the chief producers. The mineral is crushed, sifted, and washed, and
thus comes to market in various sizes. Care is taken to avoid making
undue amounts of the finest product, or *' flour," for this has less valne
than the coarser grades.

The usual test of the quality of a sample of emery or corundum, is
to compare a weighed sample with an equal amount of the standard
grade, or of some well-recognised brand ; two weighed pieces of plate-
glass of convenient size are then rubbed together with the sample
between, and the process is continued until the grit has disappeared
and the plates no longer lose in weight from the abrasion. The amount
of loss is a measure of the hardness and abrading power of the sample,
the better grade giving the greater loss.

The presence of garnet and other hard substances, not equal to
emery in abrasive power, is liable to occur in inferior sconples. The
preparation of corundum . is much more costly than that of emery,
owing to its greater hardness, hence it commands a higher prioe
(about double), while for many purposes it is not superior. Abont
9Z. a ton is the approximate market value of corundum, the production
varying around 2000 tons yearly. The annual output of emery is
probably 10,000 tons. Pure corundum is crystallised aluminium oxide
(AI2O3) ; its hardness is 9, diamond being 10. The gems, ruby and
sapphire, have the same composition.



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NON'METALLIFEROUS MINERALS. 221



FLUORSPAR AND FELSPAR.

Fhionpar. — Until the beginning of this century, fluorspar was con-
sidered indispensable in metallurgical operations. It diminishes the
I068 of metal, and was long the only energetic means of reducing the
meltmg point of slag from ores carrying high percentages of clay
or zmc. Without fluorspar very refractory ores could not be smelted
at all

Gradually, however, as blast furnaces and smelting apparatus were
improved, fluorspar was superseded by lime and other cheap fluxes,
but of late its use has been reintroduced into nearly all branches of
metallni^.

While the cost of fluorspar is six to seven times greater than that
of limestone, 1 part of flnorspar goes farther than 1 of limestone. The
former is especially effective in reducing the quantity of fuel ; it forms
two parts of slag where limestone forms three, and it forms possibly
abo fluorsilicate, wherebv heat is likely to be liberated.

While the rather high price of fluorspar prevents its use in the
production of ordinary white and grey pig iron, it has proved a rapid
and energetic solvent in blast furnace work, where it is blown in as
powder through the nozzles.

In making silicon iron, fluorspar plays a more important part.
A ferrosilioon iron, with 10 per cent, silicon, made especially in Upper
Sileeia, is almost indispensable for works that make very tough,
deep-grey castings. This ferrosilioon can be obtained in any ordi-
nary blast furnace from any silicious iron ore if it is only fluxed with
fluorspar, and the slag is strongly basic. The fluorspar reduces the
sOicon energetically; at all events fluorsilicon is formed, which is
reduced to silicon bvthe hydrogen contained in the furnace gases, and
poflsibly also directly by the coke. It does not seem impossible that
the greatly increased price of coke will result in a reintroduction of
fluorspar as a fuel-saving flux in the manufacture of foundry pig,
particularly as even a very small quantity of fluorspar added to the
charge at once raises the product to No. 1 deep-grey pig, rich in
graphite.

The remarkable property of fluorspar, that it facilitates the re-
duction of the most difierent bodies — a property common to almost all
the flnoridea — makes it a valuable flux in the production of spiegeleisen.
It has long been known that fluoride of manganese, as well as a mixture
of a manganese combination with fluorspar, can with comparative ease
be reduced to metallic manganese by means of sodium. The modem
application of this method to the blast furnace substitutes carbon for
Bodinm. A highly basic slag, lich in fluorides, seems nearly indispens«
able for the production of a rich ferromanganese in the blast furnace.

The property of fluorspar, to carry phosphorus into the basic slag,
has never been of special importance as far as pig iron is concerned.



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222 ECONOMIC MINING.

but it is utilised by the Krupp and Bollet methods of dephosphorising
pig in the basic-lined cupola-fumaoe. Whilst, at all events in the
blast furnace process, the property of lime fluoride to form an easily
melting slag with phosphates is of some importance, fluorspar, in the
process of purifying the pig iron, serves probably only as a flux for the
tdghly basic lime-slag saturated with phosphorus.

In the Thomas process too, and even in the Bessemer converter,
fluorspar is in reoent practice being added in small quantities for the
purpose of oonpentrating the slag and reducing the loss of metal ; very
great care, however, is needed to prevent such a slag from attacking
the acid lining. It is also said that in puddling in the various steel-
making methods, and in the Siemens-Martin process, fluorspar is added
partly as a slag-forming flux.

In foundry work, it is a fact that limestone, which, because of iU
cheapness, superseded fluorspar, of late is losing ground to the latter.
The limestone flux in cupola-furnace work serves only to slag the ashei
of the fuel, the sand adhering to the pig, <&c., no chemical effect on the
iron being intended. But the fluorspar affects the iron noticeablj,
keeps it grey and soft by holding the silicon as an alloy, whilst a lime-
stone flux favours the tendency of the silicon to slag. Besides, fluorspar
carries some phosphorus and sulphur into the slag. Fluorspar makee
it possible to melt inferior kinds of pig iron and a higher percentage
of scrap. But practice has shown that too much fluorspar is rather
injurious than advantageous, one reason for this being that the man-
ganese contained in the iron is thereby prevented from slagging.

The quantity of fluorspar which is added to 100 lb. of pig iron
to be remelted, is ^, or at the most \ lb. The improvement of the
product caused by this flux is specially manifest in the improTed
cupola furnaces, particularly Herbert's, which has much facilitated the
utilisation of inferior iron for soft castings. The property of fluorspar
to protect manganese does not seem favourable enough to offset the
injury due to its silicon-reducing power. Its use would, at least,
require melting in a basic furnace, or as cold as possible.

As the small quantity of phosphorus and sulphur contained in
Swedish charcoal iron, is almost entirely carried off* in the compara-
tively acid slag by fluorspar, this is of prominent importance for the
treatment of very pure qualities of iron.

Dr. Foehr states that fluorspar was formerly the most important
flux for smelting copper ores in the German stack, as well as in the
English reverberat6ry furnace. The Mansfeld copper slate, for instantei
was fluxed with up to 10 per cent, of fluorsptir, the cost of this beiu;
about 8 per cent, of the total smelting cost. The effect of this flvx
depended essentially on the volatilisation of silica fluoride, wherebT the
strongly acid slag was reduced in silicon. The iDtroduction of im«
proved and heated blasts in the Mansfeld works has almost conlined
the use of fluorspar to the blowing in of furnaces ; 5 per cent, of fluor-
spar is commonly added at the start, but the quantity decreasei
gradually, until after 2 to 5 weeks no fluorspar at all is used* The
English reverberatory furnace process fluxed formerly with as mudi
as 10 per cent, of fluorspar, but nowadays this takes place only with
ores rather rich in arsenic. Fluoride of calcium, with arsenic metak.



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NON-METALLIFEROUS MINERALS, 223

pves very volatile fluoride of arsenic, which, with a reducing flame,
BBfiily eficapes. The risk of loss involved in the volatile fluoride of
oopper necessitates the presence of excessive carbon whenever fluor-
^MT is employed in the metallurgy of copper.

While fluorspar is at present of small value in the treatment of
oopper ores containing sulphur, its property to give fluid combinations
with gypsum and barytes may prove an important means to work poor
oxides and silicious ores as well as charges containing azurite, mala-
obite, red oxide of copper, atacamite, and earthy red oxide of copper,
by reducing the smaller part of the sulphate, and forming a matte
very rich in copper, and by forcing its larger part together with the
Buoride of calcium into the slag, which thereby becomes thin and very
fluid. Equal quantities of fluorspar with gypsum or barytes produce
the most fluid slag. A significant point, particularly with poor ores
bigh in silica, is fliat this slag is poor in copper, a fact on which was
biaed the former Freiberg practice of resmelting the copper slag, to-
cher with pyrites and fluorspar, thus obtaining copper matte and
poor slag, the intention probably being to enrich the matte in copper
md impoverish it in iron.

Fluxing copper ores containing nickel, with fluorspar, is very
bvourable for the collection of the nickel in the matte, and has been
in use in the Reichelsdorf, Griinthal, and Mansfeld works. The
chemical process is still entirely obscure, and worthy of study in the
laboratory. Possibly, nickel-arsenic is decomposed into volatile fluoride
of arsenic and nickel, which latter goes into the matte. Fluorspar is
in almost indispensnlDle flux for making tough copper, and, generally,
irbenever silicon, which makes copper highly brittle, has to be removed.
&B a means to produce a matte poor in iron in the reverberatory
Ebmaoe, a mixture of fluorspar, barytes, and quartz is more energetic
Ukd rapid than an addition of only the two last named, the proportion
rf the fluorspar and the barytes being for this purpose as between one
ud three, whilst the quantity of quartz depends on how much iron
the roasted matte contains. Too much fluorspar gives a matte rich in
iron. For refining and remeltiug copper, fluorspar finds a constantly
increaaing use. Mixed with some soda, it is excellent for remelting
copper ingots, and for removing from the m)etal bath small quantities
dC arsenic and silicon. The process is kept a secret ; the refining slag
is, however, reported to be remelted with gypsum or glauber salts and
luarspar.

• In composition fluorspar is essentially fluoride of calcium, and con-
piats of 51 '3 per cent, calcium and 48' 7 per cent, fluorine. It occurs
aAably in association with lead veins in limestone formations, the
British oatput coming chiefly from Derbyshire, while the American
product is exclusively derived from the Rosiclare mines, in Hardin
oounty, Illinois. In the latter case, deposits of fluorspar and galena
occur in the limestones underlying the coal measures, in enormous and
well-defined fissure veins, the fluorspar being the more valuable portion
of the mineraL Tiie British production of fluorspar varies between
100 and 500 tons yearly, and the American between 6000 and 9000 tons,
the value being about 25«. a ton.

Fehpcar. — There are many places at which felspar is mined, or



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224 ECONOMIC MINING.

rather quarried, the product being in most instances oonsumed locally,
as the value of the article, about 15«. to IZ. a ton, does not admit of
long carriage. The mineral is a common ingredient of granites and
syenites, and is generally a bye-product of china-day works. It is a
double silicate of alumina and potash, and "contains about 64 per cent.
silica, ISj^ alumina, and 17 potash. Its principal use is in poroelun-
making.



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NON-METALLIFEROUS MINERALS, 225



FUEL.

ITuEts are of three kinds — solid, tbe most oommon form ; liquid, the,
Aost eoergetio ; and gaseous, the most easily controlled.

By good and proper firing, a utilisation of 66 per cent, of the
Boergy contained in coal may easily be accomplished,. and 80 percent.
b not impoesible. These figures may usefully be borne in mind when
ittcttflsin^ the supposed immense advantages of gaseous fuels. No
prooess €:an add to gaseous fuel more energy than it derives from the
nlid coal, in fact a loss of energy must take place in the conversion,
ind the greater utilisation, taking place in the case of gaseous fuel, is
limply due to perfected combustion, incidental to the feed being more
leadily adjusted and controlled. The consumption of solid fuel is not
likely to be affected to any extent by artificially produced gaseous fuels.

Liquid fuel, in other words, ordinary petroleum, is a very valuable
ikeating agent under certain conditions, as it contains much more
snergy, in proportion to its volume, than any other form of fuel. Its
ximposition is practically 84 per cent carbon and 14 per cent, hydro-
gen, so that its energy per lb. is about 20*860 heat-units, or 44 per
pent greater than that of good coal. In addition, it can be burned
vith less relative wuste, so that it really can give about 50 per cent,
bore duty than coal. But the available supply prohibits any idea of
ItB replacing coal in a general way.

Of gaseous fuels, the least costly per unit of heat is common
•producer" ga*», in which the oxygen for burning the carbon to
aubon monoxide is derived mainly from the air. The associated
Ktmoapheric nitrogen dilutes the carbon monoxide, making air-gas the
weakest of all useful gases, or the lowest in combustible. Next in
arder of heat-energy comes water-gas, in which the requisite oxygen
b derived from water-vapour, and hydrogen is liberated ; for equal
Ndumes, this gas has more than double the calorific power of air-gas.
third in the ascending scale stands the ordinary illuminating gas
listilled from bituminous coal, which carries more than double the
beat-energy of water-gas. Highest in the list comes natural gas, the
s^osific power of which is about 50 per cent, greater than that of
soal-gas.

The following table gives the bases for calculating the heat units
[British thermal units) developed in the burning of various oom-
PQStibles: —

Hcat.-aittBdM«lopedtntmnUDg. of combusUble. of oombutttble.

CtoCO 4,400

CtoCO, 14.500

COtiiCO, 4.325 319

HtoH,0 62,00i» 327

CH« to CO, and water 23,500 1007

C,H^ to CO, and water 21,4 159:^

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226 ECONOMIC MINING.

In making producer gas, it is possible, by utilising the sensible
heat of the eas through close attachment of producer and furnace, and
by introducing with the air blast as much steam as can be tolerated
without destroying good incandescence, to recover 60 per cent, of the
energy of primary combustion. Even counting the sensible heat as
lost, and adding radiation and other losses, stiU the gas should carrj
87 per cent, of the heat-energy of the fuel, while if the sensible heat
be utilised the figures will reach 93 per cent. The heat which 572 IW
of this gas, derived from 100 lb. of carbon, is capable of generating by
combustion is : —

GO burned to 00„ 233-33 lb. x 4,325 .. 1,009,160 heat-units.
H „ water, 4-17 lb. x 62,000 .. 258,540
Sensible heat in 572 Ih. of gas 85,800



1,353,500
Solid C bnmed to 00^ 100 lb. x 14,500 .. 1 ,450,000



Loss in conyerrion, 6*65 per cent 96,500 ^

In generating gas from anthracite coal, the products will be : —

186-66 lb. CO 807,304 heat units.

5001b.CH, 117,500

3-75 lb. H 232,500 „

Total 1,157,304

Total energy in 100 lb. of ooal 1,349,500 „

EfBciency of conversion 86 per o^it.

Heat-nnits in 1 lb. gas 2,248

In the case of a bituminous coal containing 55 per cent, carbon
and 32 per cent, volatile combustible matter, the yield should be : —

116-66 lb. CO .. 504,554 heat units.

32-00 lb. voL HC 640,000 „

2-50 lb. 155,000



Total 1 299.554 „

Total energy in 100 lb. coal 1 ,437,500 „

Efficiency of oonTersion 90-0 per cent.

Heat-units in lib. of gas 3,484

As compared with anthracite, the greater energy of bitnminoa
gas is even more than appearance indicates, since the high percentag
of hydrocarbons is associated with lower nitrogen. But the 32 p<
cent, of volatile combustible matter must be volatilised and utilise!
in its full strength, therefore it should not be suffered to cool belw
300*^ F. before it enters the combustion-chambers or regenerators,
the higher its temperature at the furnace the better.

Though water-gas cannot be produced without entailing great loi
of energy in its formation, and therefore enhanced cost per uni



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NON'METALLTFEROUS MINERALS, 227

tbttined, it possesses qualities which will ensure it a limited applica-
ion. It is made intermittently by blowing up the fuel-bed of the



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 25 of 76)