Charles George Warnford Lock.

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umbers are so soft that they can be washed without any prer^
grinding, but this is not generally the case. The calcination is oi
ducted at a red heat, and by this process the tint is made darker a
warmer, but it must not be pushed too far or the pigment will blaek

While di£ferent samples of umber present differences of tone a
shade, from a yellowish to a violet brown, they are alike in bei
very durable and proof against the injurious influences of air, li^
and impure atmospheres; ordinary acids and caustic soda haxe
appreciable effect. They mix well with other pigments without p
voking any change, and are equally satisfactory as oil or wa
colours. They do not admit of much adulteration, except in the i
stitution of an inferior grade for a superior one, and possihljj
addition of barytes as a make-weight.



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NON-METALLIFEROUS MINERALS, 319



POTASH.

"hi extensive deposits of potash salts at and near Stassfnrth, Prussia,
hich daring the last 20 years have created an important industry,
«re eDconntered in prosecuting the search for salt, and were long
igarded as a hindrance and incumbrance to the development of the
>ck-salt workings which they overlie. The deposits occur in the
onter sandstone (Triassio) series, and are illuptrated in section in
paper by my friend Mr. C. Napier Hake,* who was for some years
konected with the industry.

On referring to the section, it will be seen that rock-salt oocupies
te lowest stratum. The black diagonal lines which are drawn
TOSS the rock-salt region represent thin layers of calcium sulphate
Upsnm) 7 mm. thick and almost equi -distant. At the top of the
ck-salt and associated with its uppermost portions are thin strata
' polyhallite (trisulphate of potash, magnesia, and lime), followed
unediately by an accumulation of kieserite (magnesia sulphate^ and
lis again in ascending order by a zone of oarnallite ^double chloride

potash and magnesia) mixed with some magnesia sulphate and
ck-ealt. Towards the higher portions of the now inclined strata,
08 camallite bed gives pJace to kainite (double sulphate of potash
id magnesia combined with one equivalent of magnesia chloride and
tormingled veith 40 per cent of common salt), a secondary product
raiting from the action of a limited quantity of water on the
nuJlite layer. The upper bed of rock-salt, resting on a thick bank

anhjdrite, is also a later formation. Almost imperceptible layers

polyhallite are present in this deposit, at greater intervals than
Ofleocourring in the lower rock-scut beds; thus it has probably
Iginated from the action of water on the older deposit. Though of
nparatively limited extent, the upper salt beds are the more
teemed, as their product is much purer, averaging about 98 per
at. sodium chloride.

The primary minerals afforded by these deposits are seven, viz.
sk-salt, anhydrite, polyhallite (K0SO4, MgSO^, 2CaS0„ 2H3O),
eserite (MgSO*, HjO), camallite (KCl, K^Clj, 6H„0), boracite
^aBgOis, MgClj), and douglasite (2KC1, FeCl,, 2YLfi)\ added to
lich are nine secondary minerals resulting from their decompo-
ion, viz. kainite (K2SO4, MgSO,, MgCl,, 6H3O), sylvin (KCl),
Jhydrite (CaCl^ 2MGCI3, VlWjS), bischofite (MgCl,, 6H2O), kru-
te (K^O^, MgS04, 4CaS04, 2flaO), reichardite (MgS04, TH^O),
mberite (CaSO*, Na,S04), schonite (K2SO4, MgS04, eHjO), and
trakanite (MgS04, 46,0) ; but, besides the salt, only three of the

*" StMifart Salts and their Mode of Treatment,*' Jonr. Soc Ohem. Ind.; ii. 146.

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320 ECONOMIC MINING.

mineralB possess industrial importance, viz. the camaUite, kainite, ai
kieserite.

The oamallite region, which contains a variety of mineralB, \
chiefly contributed to the fame of these beds. It has an aTeii
thickness of about 80 ft., and consists essentially of 60 per cent a
nallite, 20 rocknsalt, 16 kieserite, and 4 tachydrite, besides sm
quantities of magnesium bromide; the several mineralB altem«ti
with each other in regular succession, in layers ^ in. to 8 ft tha
The predominating camallite contains 26*76 per cent, potassii
chloride, 84*5 magnesium chloride, and 88*74 water; when pureil
colourless and transparent, sp. gr. 1*618; it is very hygroeoopiotf
readily soluble in water (64} parts in 100).

The kainite region, though less extensive than the otheiB, k 1
of vast dimensions. The average composition of the deposit is 94
per cent, sodium chloride, 28 potassium sulphate, 15*6 magneih
sulphate, 18*6 water, and 18 magnesium chloride; in the pureststj
is colourless and almost transparent, sp. gr. 2 * 18 ; it is soluble in wi^
(79iparts in 100).

The kieserite region embraces a thickness of aboat 180 ft, i
consists chiefly of 66 per cent, rock-salt, IT kieserite, 18 csmftli
8 tachydrite, and 2 anhydrite ; when pure kieserite is amarphons i
translucent, sp. gr. 2*517, and contains 87 per cent, magnesiiim i
phate and 18 water; it is slowly soluble in water (41 parts in 1<
at 64° F.

The entire accumulations of these Stassfurth beds are supposed
have resulted from eva^ration of an inland sea, communicating w
the ocean. Ooncentration would have followed evaporation till 1
several points of saturation were reached, when each salt in ti
would begin to separate. The deposit must originally have b
basinH9haped,but has been lifted in the centre by subsequent f<ddi]
and the cavity thus created in the crest of the antidmal has n
filled by later deposits of Oolitic limestone. The mineraU are won I
a system of shiits and drifts, the latter taking the form of lul
chambers with large pillars left between them. In a distance ^
miles along the line of fault there are over a dozen shafts, and
dip of the beds varies from 40° to nearly verticaL A con^iden
quantity of the salts are sold as mined for agricultural puxposes, 1
an extensive industrv has locally grown up in oonneotion with il
purification, chiefly by solution and re-crystallisation, as described
detail by Hake. The production of kainite is about 600,000 met
tons, value 400,000Z., and of other potash salts 800,000-900,000 to
value 500,000t yearly.



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NON-METALLIFEROUS MINERALS. 321



PUMICE.

faiLE many active volcanoes eject greater or lesser quantities of
imice, these do not a£ford any appreciable proportion of the oom-
ercial supplies of that mineral. Nearly the whole European con-
onption is derived from the island of Lipari. It is found chiefly in
le northern parts of the island, on the slopes of the mountains cidled
iBta della C^ustagna, Monte Felato, and Monte Chirica, which appear
I have formed part of a great crater, formed of inclined layers of
bnes and ashes from volcanic eruptions. The stratum containing
|0 pumice is covered with a layer of stones, in some cases reaching
!0 ft thick, and being of a light grey colour, gives a singular aspect
\ the landscape. These deposits are usually worked by an inclmed
^Ikry driven in the hill-side at right angles to the dip ; from the
fitom of this, a level 6 ft. by 6 ft is driven along the strike, and,
inn this, other galleries are driven at intervals following the inclina-
on of the stratum. When one of the ealleries has reached the
Andaiy of the workings, it is filled up wim rubbish to within 18 in.
[ the top, and another gallery about 8 ft. wide by 6 ft. high is com-
pDced parallel to the first, leaving a sufficient thickness of material

Ppport for roof. When all the lower portion of this deposit has
worked away, a slioe above 6 ft in height is removeii in the
pie way, and this operation is continued until the roof of this deposit
I reached. The pumioe is brought to surface on men's backs, the
i&ers taking in turns the excavation and transport of the materiaL
be workings are usually carried on by 8 or 10 miners, who, at the
id of their day's work, divide the pumioe obtained, and carry it
km to the village of Canneto, where the principal dealers reside.

About 240 miners are engaged in this industry, and produce about
\ tons per annum per man. The deposits of pumice chiefly belong
\ the commune, which levies a duty of 3*25 lire per ton on all
morted from the island. Some of the workings belong to private
loiYiduals, in which case the miners pay a small royalty.

The sorting and preparation of the material is carried on at
Knneto. It is classified according to quality, the best of which is
dd at Messina at 40Z. per ton, whilst the inferior qualities fetch
xmi 25«. to 30«. per ton. There are also mills at Oanneto, and here
Bantities of ground pumice are obtained. About 6O0O tons is
snually exported, which, at an average value of 70 lire per ton,
qjTwaita 420,000 lire (16.800L).

In 1888 a reputedly important mine of pumice was opened up in
^ Peak of Tenerifie, Canary Islands, but it has apparently not jet
Bbfrded any supply.

Some 60 or 70 tons yearly are collected at Lake Honda, San Fran-
isco county, California, and meet the local demand.

Y

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322 ECONOMIC MINING.



PYBITES.

Under this head are included only such pyrites as are mined edelj
or principally for their sulphur contents, and utilised in the mann-
facture of sulphuric acid.

While there are many deposits of iron pyrites in most parts d
the world, they are not alwa^ accessible to mining at low cost, and
situated so that transportation . of the low-valued product is eui
and cheap. These primary conditions are esseutial to the industrial
usefulness of any pyrites bed. Further, pyrites containing any earthj
carbonates are most objectionable, as they would give off carbonic wk
in *' burning " and hinder the reactions in the chambers. Anothei
point to be taken into consideration is the physical character of tiu
ore, whether compact or crumbling, as on that will greatly depeni
the proportion of dust created in breaking, and consequent difficoltzai
or losses in burning.

The ordinary sources of pyrites used in Great Britain are : —

(a) The "coal-brasses" or pyritic nodules found in the Coil
measures ; they carry up to 36 per cent, sulphur, but average mocl
less, and being contaminated by carbonaceous matters they blacka
the acid made fix)m them, but they are low priced. I

(6) Irish pyrites, mined in the neighbourhood of Wicklow, whean
immense beds occur ; containing only 30-35 per cent, sulphur.

(c) Norwegian, shipped from Ytteroen, carrying 41 1 6 per cent
sulphur, and, though often said to be free from arsenic, &equeiitlj
showing 1 * 6-1 * 7 per cent, of that undesirable element.

(d) . Westphalian and Belgian, good as to sulphur contents, bo
also carrying • 9-1 • 8 ^r cent, arsenic. i

(e) Spanish, differmg from all the foregoing in containing sob
copper, for which the " cinders " are subsequently treated ; ridi i|
STuphur and free burning, but contaminated with 1 • 6-1 • 7 per oeni
arsenic.

Canada produces yearly 40,000 to 70,000 tons of pyrites. A3
excellent sulphur ore for acid making is mined at Finney's Iskud
Newfoundland, and is shipped to the United States. Analyses &hof
it to contain

Percent.

Sulphur 52-00

Iron 46-80

Alumina .. \ -10

Insoluble matter -40

Oxygen, moisture and loss -70

The ore is firm, bums remarkably freely, is manipulated withfiJ
trouble, and can easily be burned so that less than *5 per cent q
sulphur is left in the cinders.

The production of pyrites on a commercial scale in the nmti|
States is confined to two States. Massachusetts affords annmlfi



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NON-METALLIFEROUS MINERALS. 323

20,000 to 30,000^ tons, and Virginia 30,000 to 70,000 tons. The
Bulphiir contents is about 44 per oent., and the cost of production is
about 6«. a ton.

A scarcity of brimstone has recently led to greater attention being
paid to native pyrites in the United States, especially for the manu-
factnre of sulphuric acid for dissolving phosphates and purifying
petroleum, and some very misleading figures have been officially
published in this connection. At current prices (January 1892) and
\i points where consumed, the prices of sulphiir contained in several
products are thus given ; —

100 units of sulphur in brimstone . . .. .. $81 *00 ijSL 5«.)

„ „ foreign pyrites .. 18-15 (3Z. 15«.)

„ „ Virginian pyrites .. 14-60 (Si.).

rhese figures seem to neglect the fact that the imported pyrites carries
i2 to 53 per cent, of sulphur, and the native article only 44 per cent.

In much greater error are the computations regarding cost per
DO of sulphuric acid made from brimstone and pyrites respectively,
lie nearest approach to the truth is made by W. H. Adams, v^ho
ts^ his calculations on works situated at Atlanta, Georgia. He
rnmeously supposes H) that brimstone requires a greater consump-
ioQ of soda nitrate tnan .pyrites, whereas the opposite is the case ;
2) that the same labour will effect the handling (breaking, charging,
c) of 10 tons of pyrites as of 4 tons of brimstome — a self-evident
liBtake; and ^3) tnat the wear and tear on the chambers, &c., will
» the same with brimstone as with pyrites. Other exponents err to
f greater lengths. Adams's figures are quoted below : —

Cost of sulphuric acid from brimstone. (One day*s work) : —

4 tons of brimstone, including oosts of freight, losses in transit, &c.,\ m.^^ , ^

at$24perton | »»b OU

Nitrate of ^oda, 6 per cent of brimstone used, 538 lb. at $2*50 per\ ^n.^R

1001b. / ^^ *^

Laboor, 5 meii,at $1*25 per day 6-25

Cod. 2 tons, at 13 pr ton 6*00

Superintendent and office cost 6*00

Wear and tear 10 00

Producing 18 tons of chamber acid, at 17*65 per ton .. 137*70

Cost of sulphuric acid from pyrites. (One day's work) : —

10 tons pjrites, including costs as above, at 15 per ton 150*00

Nitrate of soda, 400 lb. at 12 -50 per 100 lb 1000

Coal 6*00

Labour 6'25

Superintendent and office cost 6*00

Wearandtear 10*00

Prodocing 18 tons of chamber acid, at 14*90 per ton .. 88*25

A common drawback to pyrites is the presence of impurities,
tably arsenic, which prevent the application of acid made from

T 2

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324 ECONOMIC MINING.

them to many pnrposeB. Nearly all pyrites contain anenicy som
eTen as much as 2 per cent. Dr. Drinrwater has described two kisd
of solphnr ore or " stone,** as it is technically called, absolutely fre
from arsenic. One was an Algerian, the other a Welsh ore. Tix
composition of the former was : —

Sulphur 44*8

lion 46*6

Insoluble 5*2

Lead 0-02

Manganese oxide 0*22

Lime carbonate 3*1

99*94

It also showed traces of nickel and cobalt.

This Algerian ore was of a greenish coloar, of a soft bharaoto
making a lai^ quantity of smalls, and difficult to bum in the kil^
It made very good acid ; bnt, with the greatest care, at least 4*5pj
cent, of sulphur remained in the burned ore.

The Welsh ore is of a different character. It is very hard, ui
difficult to break. In appearance it resembles the white p3rrit66 <
Saxony. It makes very little smalls ; bums well and completely i
the kuns.

Following is a oomplete analysis of the Welsh ore : —

Snlphnr 48*3

Iron 42-1

Inaolnble matter 5*8

Alumina 1*4

Lime oarbonate 2*5

100*1

Another specimen containing some quartz, and not, perhaps, a fid
average sample, showed only 45 per cent, of sulphur.

The burned ore sampled from a large bin with great oare, onl
contained 3 per cent, of unbumed sulphur. The great luundnei
would lead one to suspect that more than 3 per cent, would \
wasted ; but a considerable practical experience has shown this to \
otherwise.

There is no difficulty whatevei with this ore, to keep the buma
up to a full red heat.

The acid produced is certainly of a superior quality for pyriti
acid. It is of a good colour, and entirely free &om arsenic In fiM
it could not be distinguished, either by physical or chemical test
from the best sulphur acid.

The Algerian ore has apparently disappeared from the market
but this Welsh ore, raised from the Cae Coch Mine, is superior i
many respects, and will, when fully known, be largely used for tl
production of an acid which might be sold as sulphur acid.

" Becovered *' sulphur from alkali waste is always tainted witi
arsenic.



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NON-METALLIFEROUS MINERALS,



325



Br. Drinkwater examined a number of varieties of pyrites for
irsenic, and gives the following resnlts :—



Absinio in Ptbitbs.








a


6





Comiah Bkme

IriA „

BdgUm, „

Spaoi^BtoDO


percent.

•93
2-
103

•82
1-81


percent
•56

•40

•20

1-65


percent
•5

•22

•89



In addition^ most Spanish pyrites oontain selenium.

F6r estimating arsenio, Dr. Drinkwater prefers the fusion method
the oxidation with nitrio acid. After fusion, dissolve in water,
nd precipitate with washed H^, redissolving the pj^t. in carbonate
f ammonia, and again precipitating with acid, weighing on tared
Iter as AS3S3.

As a rapid and accurate method of estimating the sulphur avail-
ble to the acid maker in a sample of pyrites, J. Cuthbert Welch has
ubliahed the foUowing^in the AnaXyni :— Place '5 gmu of pyrites in a
oroelain boat in a combustion tube, heat to redness, pass oxygen*
Ter till combustion is complete, and absorb the gas formed in about
CO. of a solution of bromine in a mixture of equal parts of hydro-
Uorio acid (sp. gr. 1 * 1) and water, in potash (or preferably nitrogen)
albs. Wash out the solution into a beaker, boil, precipitate by
aQing solution of barium chloride, cool, filter, and wash, dry, and
;nite the barium sulphate.

The annual production of iron pyrites in the United Kingdom is
5,000-20,000 tons, valued at 10-12«. a ton. The cinders are deprived
r the copper, silver, and gold which they may contain, and the residue
r iron oxide is converted into an excellent pigment. In America
soot 100,000 tons of pyrites residue is thrown aside annually,
mtaining about 55 per cent, iron, 8 silica, 3 alumina, 2 sulphur,
zinc, and \ copper.

* The oxygen should be prepared from pure potaadam chlorate in glass Tessels,

at anv imte in an iron one. Kept specially for the purpose, and the gas should be

■aed through a strong solution of potash in the bulbs, through a U-tube oon-

ming oaldnm chloride, and lastly either through another calcium chloride tube

, preferably, orer phosphoric anhydride before use.



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326 ECONOMIC MINING,



BEFBACTORY MATERIALS.
(See also Clay, p, 185.)

An absolute essential in metallurgical processes connected with iron
and steel is a refractory material capable of much greater resistance
to chemical action, and possessing a far higher melting point tlian
any body which contains silica, because the latter will melt and sweat
off in the furnace, even though it be not exposed to bases that fora
fusible compounds with silica.

Lime and magnesia are in themselves as refractory to heat as the
best other materials, not a trace of melting being shown on piecei
exposed to the highest temperatui-e of steel-melting furnaces. It is a
different matter, however, when lime and magnesia are subjected botb
to chemical action and elevated temperatures.

Experience has shown that no natural product can be used directly^
owing either to uncertainty of composition or to scarcity. The
available substances* that may be used in combination or after treat-
ment are bauxite, chrome-iron, Ume, dolomite, magnesite — (when it
does not contain too much silica, which is seldom), — and artifidallj
prepared ma^esia.

Bauxite is comparatively rare, and of uncertain composition;
little silica or an excess of oxide of iron makes it fusible ; pure as
burned, it is not plastic, and must be mixed with some aluminoi
material. Thus it cannot be used on a very large scale, and has onl;
been successfully applied to the separation of the basic and ad<
materials in the basic open-hearth prooess.

Chrome-iron is used in large pieces for lining the cupolas ftic
burning dolomite, and is generally crushed and mixed with tar to
form the junction between the basic and silicious material in th«
open-hearth furnaces.

Lime and dolomite, alone or together, or magnesia extracted from
dolomite by some chemical process, seem to be the only matenab
available for basic refractory linings. Limestones will answer well
provided they contain a small proportion of clay. If the limestone is
pure, it is difficult to bum ; if too impure, it is very likely to frit a
to fuse. It has been found that 8 per cent, of foreign matters doe«
not affect it seriously, but of this percentage some should be aluminai
and as little silica as possible ; iron is to be avoided. Dolomite maj
be used either by itself or simply for the magnesia which is extracted
from it It is impossible to say just how much or how little foreign
matter it should contain to be of the greatest utility. Whether it ii
to be used by itself, or the magnesia is to be extracted from it, tha

^ T. Egleaton, *• Basic Befraciozy Materials," Trans. Amer. Inst Min. Eog^ xh.
455.



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NON-METALLIFEROUS MINERALS. 327

igher its contents in magnesia the better. Dolomite contains gene-
dlj 2-3 per cent, of silica, 2-3 per cent, of iron, and 30 per cent, of
laf^esia carbonate. Lime is expensive when burned at the same
igh temperature as dolomite ; and there is very little if any advan-
ige in nsing it.

Owing to the difficulty of finding a limestone that will answer all
onditions, dolomite is generally used, for though the magnesia is not
idiroensable, a favourable combination of constituents is usually
land associated with it. Yet it seems likely to be replaced by
rtifioially prepared magnesia. Native magnesia carbonate is costly,
Qt if it could be had free from silica, it would afford a most useful
ttterial after calcination.

\Nasum made a number of experiments under the conditions of
otnal practice on bricks made of dolomite, lime, mamesia, and
la^esite, using different binding material and additions, whose
ebon upon the base was to be examined. These bricks were pressed
Kth as little water as possible in iron moulds, dried, and were then
zpofied to the highest white heat attainable in kilns used for making
wic Bessemer brick, the shrinkage being simultaneously noted. A
art were kept in the dry air, in order to test their resistance to
inntegration.

A second set was heated to redness, when red-hot was cooled in
fiter, and was then kept in the air until it disintegrated ; while a
bird set was treated in the same manner, but, after cooline in water,
iu again heated to redness, and thus kept till the brick feU to pieces.
^ crude materials used had the foUowmg composition :

Dolomite. Magnestte.
P«r cenL Per oeoi.

Lime 31*62 1*69

Magnesia 2019 44*98

Silica 1*70 0*10

Almnina 0*09 0*84 *

Iron protoxide .. .. 1*22 1*68

Manganefle protoxide trace 0*29

Garbouioaoid 43*35 50*57

Total 100-17 100*00

LiiDMtoiie.

Carbonate of lime 98*80

Inaolnble residue 1*07

Total 99*87

The magnesia was prepared by burning the magnesite at a white
lett

Many experiments were carried out with each of these four
ftaterials, in order to test the action of clay (with 49*4 per cent.
Oica^ silica, phosphoric acid, oxide of iron, sesquioxide of iron,
ttqmoxide of manganese, and a basic converter cinder.

The latter had the following composition : — 8*14 per cent, silica,
18*25 lime, 4-65 magnesia, 15*84 phosphoric acid, 9*48 protoxide



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328 ECONOMIC MINING.

of iron, and 6 * 14 peroxide of iron. In the case of dolomite the inTes-
tigation embraced experiments on the action of protoxide of iron,
phosphate of protoxide of iron, and phosphate of peroxide of irosu
Wasum tabulated the resolts, and draws from them the following
conclusions : —

(1) Oood brick may be made of dolomite, limestone, and of mag-
nesia burnt at a white heat, without the addition of any binding
material. This, however, is not the case with magnesite, because
the latter, when ground, is not sufficiently plastia Much finer brids
are obtained when clay is added ; and under these conditions, eTeii
magnesite yields faultless brick. Unless the new material used las
the manufacture of the brick is very inferior, the addition of clay may
go as high as 5 per cent, without materially affecting the re&actory
character of the brick. They must be burned at the highest white
heat for a long time.

(2) Dolomite and lime bricks, made without any binding material,
will, on an average, last 3 weeks in dry air. Bv the addition of day.
their durability is materially increased. Bricks made of magnesia
or magnesite, with or without clay, last more than 3 months. Tbe



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