Charles George Warnford Lock.

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Soluble as follows : carbon bisulphide and chloroform dissolve it
completely ; benzol dissolves 95 per cent. ; ether, 86*5 per cent. ; abso-
lute alcohol, 9*5 per oent.

The output in 1892 was about 1500 tons, which found a ready
market at lOJ. a ton in St. Louis. Mixed with turpentine in the
proportion of 1 lb. to 5 pints turpentine, and heated, it makes an
excellent japanning varnish.

The total production of American asphalt is now about 40,000 tons
a year, worth 21<. a ton.

A variety of bituminous substances, from pure hard asphalt to
fluid petroleum, exist in immense quantities along the coast of the
Golf of Mexico, chiefly in the States of Tamaulipas, Vera Cruz, and
Tabasoo, but there has been no organised effort to utilise the deposits.
Almost inexhaustible beds of asphalt exist on both banks of the river
Thsmeei, about 60 miles above Tampico, in a comparatively pure state,
and containing only an insignificant proportion of foreign matter.
Asphalt, or ckapopote^ as it is called in Mexico, is frequently found
floating in masses on the rivers and lagoons, and is cast up on the
beach by the waves aU along the Qulf Coast, and especially in the
ridnity of Tuxpan, and on the Orijalva river in Tabasco, and sold at
the rate of St. to 9s. per cwt.

In many other places asphalt occurs, and is used locally as fuel.
This is notably the case in Cuba.

When the bituminous matter is to be sold as pitch, it requires to
(mdem> some purification. Usually, i^is takes tne form of melting
in boiHng water, by which the pitch is made to float and may be
ikimmed off and poured into moulds, while the sandy matters have
a tendency to collect at the bottom of the vessel. If the earthy
matters are very fine-grained, their superior specific gravity is not
oonmcuonsly exercised, and repeated meltings may be needed to effect
anyuung like complete removal of impurities. Sometimes boiling
ahale oil is employed as a substitute for the hot water, especially if
the crude pitch contains much water, as by this means separation of
both earthy matters and moisture is accomplished in one operation.

The chief consumption of asphalt is for paving purposes, either
alone or in oonjunction with gritty materials. It is claimed that the
bituminoos sandstones afford a better foothold for horses than the
hitominous limestones, as they never wear so smooth. Much so-called
"* a^halt " b simply coal-tar concrete.



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174 ECONOMIC MINING.



BORAX.

Though the term " borax " is properly applied only to minerals con-
sistine essentially of soda biborate, it forms a convenient heading for
the whole class of boracic products, more especially as their uses are
practically identicaL

While there are many minerals which contain more or less boracic
acid in various combinations, commercial supplies are obtained only
from about half-a-dozen, chiefly as follows : —

Borax or tinkal, soda biborate, Na20,2B203 + lOHjO, containing
36*65 per cent, of boracic acid.

Ulexite or boronatrocalcite, calcium-sodium borate, NaCaB^O, +
5HaO, containing 49 • 7 per cent, boracic acid.

Priceite, calcium borate, 4BO3, 30aO,6HO, containing about 49 per
cent, boracic acid.

Pandermite, calcium borate, 2CaO,3Bj,03,3H20, containing 55-85
per cent, boracic acid.

Stassfurtite, magnesium borate, 2^^^^^^+ MgCl,, containing
60*75 per cent, boracic acid.

Sassolite, boracic acid, H3BO3, containing 56*45 per cent, boracic
acid ('anhydrous).

Tne tinkal trade of Central Asia is very remarkable. The borax
does not effloresce on the upper surface of the soil ; the upper efflor-
escence consists principally of soda sesqui-carbonate and sulphate, with
more or less chloride. Under this is the borax, which appears as a
greasy greenish-yellow substance, never exceeding 2 or 3 in. deep, and
is underlaid by a deposit of inferior material.

The borax and salt fields of Gnari or Hundes, in Thibet, lie to the
north of Bongbwa Tal, in the eastern part of the Zjang of Bohtoh
^Rudukh), and at the Chapakani lake. The two salts are obtained
trom different spots in the same vicinity, and are both worked in the
same way by lixiviation from the earth taken from the surface of the
ground in which the salts are developed by natural efflorescenoe.
These salt-fields are open to all who choose to adventure their labour
in them on payment of one- tenth of the produce tu the Lhassa (Govern-
ment, who have an excise establishment on the spot. The borax is
collected from June to September and sold at the different fairs, at
Ganpa, Oartoh, Sibilam, Ghajna, Taklakhar, Dabakhar. It is brought
down by the Bhotiya traders and purchased by the merchants of
Bamnagar, where it is refined. The transport is an exceedingly
arduous and hazardous undertaking, mostly performed by pack-she^
The refining process is as follows ; — The tinkal is pounded, placed
in shallow tubs, and covered with water to a depth of a few inohes;
to this is added a mixture of about 2 lb. lime in 2 pints water, for
every 10 maunds (820 lb.) of tinkal, and the whole mass is well stirred



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NON'METALLIFEROUS MINERALS, 17S

eyeiy 6 hours. Next day, it is drained on sieves or doth, and after
thia is again dissolved in 2^ times its weight of boiling water, and
tbont 16 lb. lime is added for the above quantity. It is then filtered,
boiled down, and subsequently crystallised in funnel-shaped vessels,
nsDally of ftafwa, an alloy of copper and zinc or lead. The loss in
weight is about 20 per cent. The yearly contribution to European
supplies is about 500-1000 tons.

A great deal of adulteration takes place among the native dealers,
to the detriment of the reputation which this article has always had
among potters.

The American sources of borax have latterly come into prominence.
The depressed alkaline plain, known as the Oreat Basin,* contains,
along the Nevada-California border, and in California, at least ten
bondferous '* salines " or marshes. These marshes are the old beds of
relatively restricted lakes, which received boracic water, probably
from hot springs. Volcanic phenomena are abundant io the region,
and were doubtless the principal stimulating cause. Borate of lime
and soda (nlexite), borate of lime (priceite), and borate of soda (borax)
are all found, and always mingled with dust, and more or less gypsum,
Bodiom carbonate, sodium chloride, sodium sulphate, and various other
ailaline salts. Artesian wells have shown standing water at no great
depth in some of the marshes, and in at least one instance it is charged
^^ borax. The crust of borax is often renewed on the surface after
it has been removed, and after an interval of 3 or 4 years may be
gathered again. This is due to capillary attraction through the pores
of the underlying soiL

The best known of the salines in Nevada are Teel's Marsh,
Cohunbus Marsh, Fish Lake Valley, and Khodes Marsh, all in
Esmeralda Coun^. Although the marshes cover thousands of acres,
the portions productive of borax are comparatively limited.

There is a minor deposit at Salt Wells, in Churchill County,
Nev^ and in California there are three marshes in Inyo County — ^the
Saline Valley (said to be the largest of all), the Amargosa, and the
Furnace Creek ; one in San Bernardino County, the Slate Range or
Searie's Marsh ; and one, of less present importance, at Little Borax
Lake, Lake County. The last named is north of San Francisco.
Borax is also shown by analysis to be present in the water of Owen's
Lake, and boraoic acid is found in the water of Mono Lake to the
extent of *16 grm. per litre. The total American output is about
5000 tons yearly.

Great quantities of borax crvstals have been dredged from some
of these lakes, in addition to the product obtained by boiling the
water to crystallisation. A "fissure vein" 7-10 ft. thick, carrying
calctum borate, is being mined near Calioo, San Bernardino County,
Oslifomia.f

Befining the crude borax consists in collecting the material from
the plain, by simply shovelling layers of the surf^oe to a depth of
18 in., and loading it into waggons provided with wide tyres to the
wheels. Below the surface of the marsh at a depth of 4 ft, liquor is



* C. Napier Hake in Jl. Soc. Chem. Ind^ viii. 854.
t Report State Mineralogist, 1893, p. 845.



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176 ECONOMIC MINING.

found highly impregnated with borax. The material is hanled to the
refining works, which are conveniently situated upon firm ground at
the edge of the marsh, and where the next step consists in dissolying
in water all the soluble matter in the crude material. For this
purpose wrought-iron pans are used, about 35 ft long by 7 ft. wide,
semicircular in shape, set on arches of stone, beneath which are
furnaces and flues for heating the contents of the pans. The orade
borax is thrown into the pans, and with the aid of long poles is
vigorously stirred until all that is soluble is dissolved ; the liquor is
then allowed to settle for some hours, and when perfectly clear
is drawn off into round tanks made of light galvanised iron, where
the borax crystallises on cooling. When the crystallisation is
complete, the "mother liquor" is drawn off, leaving only the
crystalline borax, which is removed and packed into sacks for
commerce. The total cost of production is said not to exceed 5l
a ton.

There is no difficulty in refining crude borax, but with ulexite it
is a different matter. This can be changed to. sodium borate bj
boiling with sodium carbonate, but losses ensue from the reacticm
being incomplete, so that various other processes have been devised
Steam, when superheated and passed over ulexite, volatilises the
boracic acid and yields sassolite. In the Formhals prooess the fome^
of bumine sulphur are introduced into a hot emulsion of ulexite ii*
water : sodium sulphite and sassolite are yielded. In the Bobertsoij
process there are conducted into a similar emulsion the fumes whicU
are employed in the usual manufacture of sulphuric acid. In the
Gutzkow process the ulexite is first treated with sulphuric acid, and
then the gypseous residue is distilled with superheated steam. Bal
by whatever process the solution of borax is procured, some
precautions in obtaining its crystals are necessary. Thus, borai
(Na2O,2B2O3+10H2O) crystallises best when an exoess of sodina
carbonate is added to the solution, equal in amount to 5 per cent oj
the resulting borax. Bat if the excess be too great, the neutnl
borax (NaBOs+^H^O) results. Further, if the hot solution exceed^
24°-28° B., octahedral borax (NapB^OT t SHjO) is formed. For largi
crystals, slow cooling in capacious vats is necessary. For smd
crystals, small vats, which are kept in agitation, are best. Ira
tanks are undoubtedly preferable.

As to the relative merits of the various processes referred to ii
the last paragraph, it may be observed that by the use of hydru
chloric or sulphuric acid, a pure boracic acid is easily obtained, whicl
with soda gives fine clear lyes. The voluminous slimes of caldnii
carbonate are done away with, because when hydrochloric acid i
used calcium chloride is formed, while when sulphuric add \
employed calcium sulphate is produced, forming a heavy precipitatl
which settles to the bottom. Farthermore a considerable saving o
soda is effected, because a large part of the soda used in direct boiliiu
is required for the conversion of the calcium sulphate into cald^
carbonate. But there are just as weighty grounds against thi
method of manufacture. In the first place we must consider tb



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NON^METALLIFEROVS MINERALS, 177

wear of the factory when acids are used. A second reason is the
volatility of the boracic acid with steam, which causes considerable
]o», and finally soda is so cheap and pure that an increased con-
Bumption is of no great importance. The great point in adopting the
simple boiling with soda carbonate is to leach in boiling water the
Blime-cakes from the filter presses.*

Boronatrocalcite is fonnd in inexhaustible deposits on the high
plateaus of the Cordilleras in northern Chili It is mined at
Maricunga, Pedemal, and Acostan, and these places supply almost all
the calcium borate which is shipped to Hamburg ma Antofagasta.
The borates which are brought from Bosario (Argentine Eepublic)
are also mined near Acostan, from a deposit at Tecuman on the
Argentine side of the Cordilleras. This boronatrocalcite contains 18
to 24 per cent, anhydrous boracic acid, the higher grade being worth
about 18i, a ton. Chilian exports of borax range from 30 to 3000 tons
a year, and of calcium borate from 3000 to 6000 tons annually.

Pandermite occurs in a bed occupying over 13,000 acres, near
Panderma, Asia Minor, and is being extensively worked. The field
is situated in a basin of Tertiary age, surrounded by volcanic rooks,
which vary from granite on the east to trachyte on the north, and
oolnmnar basalt on the west. Several basaltic hills and dykes protrude
in different portions of the basin, and the presence of hot and mineral
springs further testifies to the volcanic influences which have been at
work, and in which, doubtless, originated the boracic mineral. The
latter occurs in a stratum at the bottom of an enormous bed of
gyptnm, its greater specific gravity probably impelling it downwards
while the whole mass was yet in a soft state. Several feet of clay
cover tb© gypsum bed, which is here 60-70 ft. thick, though in
places it attains to double that thickness.

The boraciferoDs stratum varies in depth, it has been proved for
a vertical distance of 45 ft. The mineral exists in closely packed
modules, of very irregular size and shape, and of all weights up to a
ton. It can be applied directly in place of borax, and is more
wonomicaL The yearly output is about 8000 tons.

The boracic acid lagoons of Tuscany have been repeatedly
described. They occur in a volcanic district of limited extent. The
inost abundant supplies are obtained from artesian wells, which
invariably strike the boracic vein at a short distaooe from the
«nrfeoe. The boring, however, is carried down until the well yields
water, when the machinery is withdrawn, and water is let into the
rfiallow pond previously dug around the bore hole. This water very
<KH)Q becomes heated up to boiling point, and impregnated with the
horacic acid, which rushes up from the opening of the artesian well,
*ft«r which the water is drawn off" and evaporated by passing it over
t series of 15-20 shallow metal pans, aiTanged like a cascade. The
horacio add as it reaches the bottom pan is half solidified, and when
«oW, has the appearance of being frozen over with a skin of rotten
ice. This skin is removed and strewn on the floor of a drying-house
Ideated by hot pipes, and by this means the boracic acid becomes

• See also Spons* * Enoyclopiedia.' p. 526.

N



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178 ECONOMIC MINING.

orystallised. The lagoons have a most peculiar aspect during tbe
issuing of the boracic vapours. Wlien full of water, the boiling is
continuous, rising to some feet in height, but the vapour is quite
clammy and unpleasant from its sulphurous odour. The production
is about 3000 tons of crude boracic acid per annum, containing
84-89 per cent, of crystallised, or 46^-60]^ per cent, of anhydrous
boracic acid, worth 252. a ton, in addition to 1000-2000 tons of borax.



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NON'METALLIFEROUS MINERALS, 179



BROMINE.

This substance is not met with in the free state in nature, bnt always
in combination as bromides, notably as magnesium bromide. Bro-
mides are present in small quantity in all sea water, but the chief
sources of the European supplies are the kainite beds of Stassfnrt.
The raw salts are dissolved in water, and when the potash and soda
chlorides have crystallised out, magnesium bromide remains in the
mother liquor. Through this liquor a current of chlorine gas is
passed, and the bromine is distilled off.

The brines produced in the salt regions of West Virginia and
Pennsylvania, in Midland County, Michigan, and in the Tuscarawas
Valley and Pomeroy, Ohio, contain so large a proportion of bromides
that it is profitable to save them and prepare bromine as a by-product.
All the bromine produced in the United States comes from these
sources. The bromides in the brine are concentrated in the bittern
druing the process of salt manufacture. The bittern, at a specific
gravity ranging from 36® to 42° B., is treated with sulphuric acid and
black oxide of manganese (pyrolusite), the amount of reagents used
beiog dependent upon the percentage of bromides in the bittern. The
nilphnric acid combines with the base of the bromide and forms
hydrobromic acid ; the latter is oxidised by the pyrolusite with the
eTolntion of bromine gas, which is collected and condensed in suitable
vessels. In Michigan, potassium chlorate is the favourite oxidising
agent, because of the large proportion of calcium chloride in the
liquor. A detailed and illustrated account of the manufacture will
be found in Spons' ' EncyclopsBdia.'

At the places named the bittern is very rich in bromides, the
estimate being that for every 2 barrels of salt 1 lb. of bromine should
be made. This, however is not strictly correct, as it differs in different
localities and at wells in close proximity. The material at every salt
well where bromine can be made is now worked, and the production
is as large, probably, as it will reach, unless salt should be found in
other places containing it.

The annual production amounts to about 400,000 lb. in America,
400,000 lb. at Stassfurt, and 300,000 lb. in Scotland and Ireland from
seaweed. The trade is in few hands, and the price is about 9(2. a lb.



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i8o ECONOMIC MINING,



CEMENT.

Cements are a group of mineral substances oonsistiug essentially of
argillaceous magnesian limestone or of mixtures of clay and lime,
which, after calcination, possess the property of hardening in contact
with water, this property being due to the crystallising energy
developed by combination of water with the silicates of lime and
alumina formed by the calcination.

It is usual to divide cements into two classes, Koman and Port-
land, the former being derived from natural rocks and the latter from
artificial mixtures, but inasmuch as some Portland cements are now
made from natural rocks, a better classification is ** natural" and
«* artificial."

Natural hydraulic cements are made from (a) nodules of calcareous
clay called "septaria," found in clay beds of Lower Eocene age
(Tertiary), and from (6) argillo-magnesian limestones occurring abun-
dantly for the most part in Tipper Silurian rocks. The analyses
given on the next page illustrate the divergence in their compositioD.
All but the two last (from Lehigh Valley) contain much magnesia
and are made into Eoman cement. The Lehigh rocks afiford Portland
cement.

The process of manufacture consists in quarrying and breaking
the rock, calcining in kilns, which are usually continuous in operation,
and grinding. The burning is light, and usually not strong enough
to expel all the carbonic acid in the rock. The cement until ground
is simply a mass of partially vitrified clinker, which is not affected by
water. It is only after it is ground that the addition of water in-
duces crystallisation, of the silicates formed by calcination. The
dej^ree of fineness is wholly a matter of economy. Coarse particles
will have no " setting " power, and may for practical purposes be con-
sidered as so much sand. The usual demand of finene«>s is that 90
to 95 per cent, shall pass through a sieve of 2500 meshes to the square
inch. Colour is not now regarded as of much importance, except that
a yellowish tinge may indicate insufficient burning. Colour is chiefly
due to iron and manganese oxides.

If the rock contain too great an exoess of clay, the resulting
cement will be quick-setting, soon attaining its maximum hardness.
Such cements have but limited tensile streno^th and deteriorate by
age. In burning such stone, a heat hardly sufficient to drive off the
carbonic acid can be used : if greater, a slag is the product. If the
limestone contains an excess of lime to clay, a greater neat is required,
and when such cement is used it swells, and if water is allowed to act
upon it in situ, the free lime hydrate washes out, thus weakening the
mortar. What is required is a stone in which the lime and clay are
in such proportion that when burned they will chemically react on
each other, forming silicates and aluminates of lime. Such a natiural

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1 82 ECONOMIC MINING.

9 ft. 6 in., then contracting for the next 7 ft. till top of pit is reached
to 3 ft. The discharge is 3 ft. high by 2 ft. 6 in. wide. The kiln is
lined for the first 12 ft. from the top with firebrick, the remaining
distance with well-burned common brick. Coke, anthracite, or semi-
bituminous coal can be used.

The kiln is fired up by placing about 3 ft. of cordwood in the
lower portion of the kiln. Overlying the wood, a thick layer of rock
is placed for about 1 ft, then a thin layer of coarse coal, and from
there up alternate layers of coal and rock. This coal or coke should
be broken up quite fine. After the kiln is running smoothly, 1 ton of
coal will bum about 13 tons of rock, or 55 to 57 barrels of 300 lb.
each. The size of the stone should not exceed 6 in. any way. The
kiln is drawn at the bottom twice every 24 hours, raw stone and fuel
being added at top after each drawing.

Natural cement should weigh 49 to 56 lb. per cub. ft., and set in
2 to 30 minutes. It should give a tensile strain of over 85 lb. when
immersed in water 7 days, showing a gradual increase up to one year
or even longer.

Artificial cement is made from mixtures of clay and some form of
lime carbonate, usually chalk. It is practically a double silicate of
alumina and lime. There are three methods used in Europe to
reduce the raw material to the required degree of fineness, known as
the '* wet," ** hemi- wet,'* and " dry " processes.

The '* wet " method is principally used on the Thames and Med-
way. The chalk is first passed through rock-breakers and then
ground wet in Chili mills, from which it is passed to the wash mills,
where the requisite days and water are added. The wcwh mills are
large circular tanks with arms or racks revolving in them. Through
this agitation the combined materials are thoroughly incorporate,
and rendered about the thickness of cream. From the wash mill the
mass is allowed to flow to the reservoirs. After the ''slum" or
" slurry " has settled, the water is drawn off, and the residual " slurry"
is allowed to evaporate till it becomes a thick mud. From thetie
reservoirs it is carried to the dry floor, where all i-emaining crater is
expelled, and it is then broken in pieces the size of a brick. The
great disadvantages of this process are (a) the limestone and clay
being of difierent specific gravities separate from each other, (6) large
areas of land are required for reservoirs, (c) excessive labour in hand-
ling and re-handling, (d) the time from the first manipulation of the
raw material till it is ready for kilning is months. Nevertheless it
continues to be used by many of the original works.

In the semi-wet method the chalk and clay mixture is passed
through the wash mill with as little water as possible, and after
being intermixed, is conveyed to millstones, from which it flows to
the drying plates, where it is dried and is then ready for the kiln.
Even by this process large areas of dry floors are required, as weD as
labour, time, and fuel.

In the dry method, the dry raw materials are mixed in their
correct proportions, passed through rock-breakers which feed rolls,
and from here the yet coarse powder is conveyed to millstones, by
which it is reduced to such a fineness that 80 per cent, will pass

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NON-METALLIFEROUS MINERALS, 183

through a lOO-inesh screen. From the stones it is elevated to bins,
whence it is carried by double conveyors to pug mills.

During this passage to the pug mill suJQScient water is added to
make the particles firmly adhere together. From the pug mill it is
carried to the dry house, and is ready for the kiln in 24 hours.

In place of *' pugging,'' the mixture has a little water added, and
is conTeyed directly to a dry brick press, from which it comes ready
for the kiln.

The advantages of the " dry process " are (a) the rapidity with
which the materials can be combined ready to bum, (6) the saving of



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 20 of 76)