Charles George Warnford Lock.

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

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D in shallow wooden vats, usually provided with movable wooden
overs, which serve as a protection during winter and rainy weather,
^he Syracuse works, the most extensive in the United States, have an
7aporating surface of over 12,000,000 sq. ft.

The expense of making salt depends on the strength and quality
f the brine employed, on the kind of fuel and its price and quality,
a the kind of labour and the cost of the same, on the weather, on the
ear and tear and the original cost of the plant, and, finally, on the
aality and quantity of the salt made. From these considerations it
i evident that the manufacturing price per barrel or ton of salt is
ifierent in every locality and individual saltwork. In Syracuse
ton of anthracite dust wiU produce 8 to 10 barrels of salt ; in the
estem part of the State, 13 to 15 barrels. In West Virginia and the
hio Valley, the product is 5 barrels; in Michigan, 14 to 15 ^barrels
"e made with the same coal. To make a barrel of ordinary common
ae salt, including barrel, costs in Syracuse 55 c. to 60 a ; in Western
ew York, 45 c. to 50 c. ; in Michigan, 25 c. to 30 c, where wood, which

the refuse from saw-mills, has been used as fuel. For artificial
raporation, anthracite dust, bituminous coal, and wood have served.

The production of salt in the United States has steadily risen
wn 7,000,000 barrels (of 280 lb.) in 1885 to over 10,000,000 in 1891.

The rig adopted for working American brine wells is a duplicate
that described under Petroleum (see p. 280). The rate of pumping
regulated so that the brine is delivered with 25 per cent, of salt.
I it comes up it is full of gas, which is mainly nitrogen with a small
oportion of hydrocarbons. The bore-holes are arranged in fours at
e comers of a square, wiih a diagonal of 200 ft. The brine is
livered into a large storage and settling-pond, whence it flows into
eet-iron evaporating pans. 1 ton of salt costs Is, in labour and
cwt. of coal, in adcdtion to ^ cwt. of coal for pumping. By this
stem, the cost of a brine well 1000 ft. deep, including the rig, is
002., and it is drilled in 3 weeks. Some wells bored by the diamond
ill, on the other hand, cost 30002. each, and took 3 months to make.
le system presents, tiierefore, great advantages, especially where
lee nave to be numerous, and where it is not certain how long a
^1 will retain its productiveness. On the other hand, in making
eliminary explorations of a new district, the diamond drill is
perior, because it famishes actual cores.

There are many other localities where conditions favour the natu-
l separation of salt from sea- water or brine, but nothing regarding
em is of such a special or remarkable character as to deserve de-

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Two saUne mineralB of great utility and limited distribution ar
commonly known by the one name of saltpetre, though they diffie
essentially in composition. The more abundant is the South America
saltpetre, or sodium nitrate ; its Eastern ally is the nitrate of potadi

Soda nUraU. — Often called <* Chili saltpetre," nitrate of soda oocoi
along a considerable stretch of the Pacific ooast-line of South Amerioi
not confined to Chili alone. The saline beds so characteristic of tb
region are later in a^e than the Tertiary period,* and appear at intei
vaTs scattered over the whole of that portion of the western ooast o
which no rain falls, extending entirely through the desert of Atacanu
and stretching more than 550 miles north and south ; their greatea
development appears, however, between latitudes 19® and 25** S.

They are generally superficial, but occasionally reach to som
small depth below the surface, and then may be entirely covered ove
by diluvial detritus ; they always, however, show signs of their ci
istence by saline efflorescence on the surface of the ground* whic
often covers vast plains as a white crystalline incrustation.

The salts forming these *' salinas," as they are generall j t&nosi
are combinations of the alkaline and earthy bases, soda, lime, magu
sia, and alumina, with hydrochloric, sulphuric, nitric, and oarbonj
acids — and occasionally with boracio, hydriodic, and hydrobromi
acids — and in combination present themselves as the foUowin
minerals in a more or less pure state: — Common salt, epsom-sal
glauber-salt, thenordite, glauberite, soda-alum, magnesia-alum, ^
sum, anhydrite, along with calcium chloride, sodium iodide, bromi^
carbonate, and nitrate, and in some places lime borate and borax.

With the exception of the boracic acid compounds, all the minei
substances found in these "salinas" are such as would be left
evaporating sea-water, or by the mutual reactions of the saline mai
thus left on evaporation on the lime, alumina, and organic matl
found in the adjacent rocks, soil, and shell-beds ; and bea^ring m mi
the recent elevation of the whole of this coast, and that no rain hXi
in these regions, it appears very reasonable to suppose that all the^
saline deposits owe their origin to lagoons of salt water, the oommi
nication of which with the sea has been cut o£f by the rising of t£

The deposits situated at about 2500 to 3500 ft above the preseii
sea-level include the important beds of nitrate of soda, showing theri
selves, according to the configuration of the coxmtry, at distance
varying from 10 to 40 miles inland.

The first step in the formation of nitrate of soda appears to I
the decomposition of the sodium chloride (salt) by lime carbonate (i

• D. Forbes, ** BoliYia and Peru," Pioc. Gaol. Soc, Nov. 21, 18Ga |

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he fbnn of shell-Band, fto.) with the production of chloride of ciil-
mm and carbonate of soda, both of which salts have been shown to
« present in quantity in the soil of these nitrate-grounds.

The soda carbonate thus eliminated, when in oontact with the
lixtme of shell-sand and decomposing vegetable matter which may
16 expected to result from the luxuriant vegetation around a tropical
ramp, and from the abundant marine plants in the lagoon itself,
ronld realise the conditions of artificial nitre-beds, substituting only
oda carbonate for the potash carbonate there used.

In seeking for nitrate of soda, the searchers always look to the
[nng ed^e of such salt- basins, and further judge of the probability of
nding Uie nitrate from a peculiar moist or clammy state of the
roima, which is due to the presence of the calcium chloride produced
^ the decomposition above explained.

The mineral containing siEiltpetre is called "caliche." Caliche
enerally lies at depths of 3 to 30 ft. below the surface, and sometimes
leembles in appearance loaf sugar, and at others rock sulphur ; and
Kain it appears white, crossed with bluish veins. Its sp. gr. varies
om that of common salt to sandstone (2*41 average), according to
le amount and nature of earthy matters it may be allied with. The
Jnable mineral is found beneath a covering of calcareous earth,
merally assuming the appearance of half-formed sandstone, when it
serviceable for building purposes. A shaft, or hole, sufficiently
ide to permit of the passage of a man, is sunk through this cap as
r as the under side of the caliche, at which point the underlying
rth is dug out in a circle for several feet. The chamber thus formed
chaijzed with gunpowder (manufactured in the district), and on
ing &ed the result is to disengage and throw up to the surface the
bterranean caliche, which is picked out by hand and stacked up in
aps at some convenient point, whence it is conveyed in carts,
pable of holding about a couple of tons, to the " oficina," or manu-
^ry. Considerable skill is required in selecting the points where
begin mining operations, and it frequently occurs that large sums
moDcy are paid for lands which on being worked prove to be
tfthless, either on account of the scarcity of the caliche, its bad
ality, or its great depth beneath the surface. These losses are sus-
mi on account of the difficulty sometimes experienced in obtaining
)OTir and tools in a countiy so inhospitable in its resources, and
nessing no real indigenous population.

The <»liche lies in beds varying from 6 in. to 12 ft. thick. No
iche bed is found nearer to the sea coast than 15 miles, and the
thest beds are distant 90 miles. The Ramirez caliche is plenti-
and easy of extraction ; it contains 51 per cent, nitrate of soda,
common salt, 6 sulphate of soda, 3 sulphate of magnesia, and 14

At the ofidna the caliche is broken by hand or by jaw breaker
io cubes that will pass a 1^ in. ring. ThcDce it goes to the boiling
08, which, in all factories under European management, are steam-

Great diversity of opinion exists among saltpetre manufacturers
on the most economical form of "cachucha" or boiling-pan. Some

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advocate the cloeed cachucha, which in every respect may be ocHnpai^
to a steam chest, because they maiutain that, the steam bding endoflei
there is no waste of heat, and consequently an economy is effected i
coah Their opponents assert that the steam in the cachncha oondenie
and thereby weakens the solution, and that it prevents a most impo
tant operation — the stirring-up of the matter during the boiling. (^
the other hand, the open cachucha allows the steam which has pasM
through the caliche, and done its duty, to escape into the air, a
enables the attendants, during the entire boiling, to constantly tm
over the caliche, thereby enabling the heat to penetrate into evei
crevice of the mass. The result is to extract more nitrate from tl
caliche, and less is thrown away in the ripia or refuse ; henoe, by tl^
latter system, an economy is effected in caliche, which more tlu
balances the extra consumption of fuel.

In the closed cachucha the caliche is first placed in boxes made <
perforated iron plating, which are mounted on wheels, and are poak^
along a tramway into the cachucha. To overcome the difficulty I
stirring up the mass, boxes have been made of a circular shape, a^
capable of revolving on their standards when locked to an axle workt
by a wheel on the outside. This plan, however, proved a failure, i
account of the accumulation of insoluble matter at the bottom of t|
cachucha, which completely wedged in the boxes, and the attempt j
give the latter a rotary motion could only have been done at the li^
of breaking the couplings and damaging the boxes themaelveB. TU
plan might be carried out by making the plant stronger, and \
allowing adequate space for the insoluble matter which escapes fra
the boxes ; but then that would be objectionable, on acoonnt of t^
large steam space it would afford in the cachucha, and the oonsequd
impoverishment of the solution through the condensation of thesteti

There are other forms, known as egg^baped cachuchas, owing \
their similarity in form to an egg placed on its smaller end. The
offer great facilities in the operation of charging and discharging tl
material. The caliche is conducted over a road to their upper part, ai
shot down. After being boiled, the solution is tapped, and the refu
is allowed to fall into trucks placed beneath, which convey it to ti
spoil bank. The chief disadvantage of these cachuchas conaiBts in ti
necessity of having at command considerable height for the appnw

An ideal English factory is the Bamirez, Korthem Chili, built 1
Bobert Harvey, with a productive capacity of over 6000 tons a mont
The plant comprises 6 steel boilers, 12 boiling tanks, 90 crystalliBi]
tanks, a 5-compartment washing tank, 8 large circular tanks, ai
3 crushing machines, as well as locomotives and rolling stock. Owii
to the salt and other solvents contained in the soil, great oaie w
bestowed in preparing the foundations for the carrying walla. Tl
caliche is extracted according to Shanks's lixiviating system, ai
when the solution is at llO'^ Tw. it is allowed to settle for a sbo
time, and then is run off to the crystallisation tanks at a temperatn
of 240** F. The crystallised nitrate, after the mother liquor b
drained awa^, is transferred to drying floors, where it becomes pe
'— *iv dry in the tropical sun, and it is then filled into sacks i

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ipori The cost of the machinery, plant, and oonstmction amounted
) 110,000/.

The total exports amount to abont 1,000,000 tons per annnm — 90
er oent to Europe, and 10 per cent, to the United States ; the value
Qctnates somewhat, bat averages about 92. a ton. Its principal con-
unption is as a fertiliser and in sulphuric acid manufacture.

^dU;^ mirate. — True saltpetre is nitrate of potash, and is found
biefly in India.

The generally accepted conditions necessary for the formation of
kltpetre are (1) the presence of decaying organic matter, whose de-
nnpositioD affords a supply of nitrogen ; (2) access of atmospheric
ir to oxidise the nitrogen into nitric acid ; (3) sufficient potash in an
nOable form (such as wood ashes or decomposed felspathic rocks)
)r the nitric acid to combine with as fast as it is liberated. Given
^ conditions, the formation of the salt will take place in very
uied situations, being most commonly observed in countries where
tropical climate fiEivours the decomposition of organic matters.

In the neighbourhood of Ak Serai and in other localities in Asia
[inor, saline efflorescences occur in considerable quantity, usually
iKxnated with recent volcanic phenomena, and afford saltpetre whicn
I employed in the local gunpowder factories.

Tnming to India, we find that some saltpetre is obtained from the
tiny mud deposited by the Biver Ganges during the flood season,
aalysis of a nitrous earUi from Tirhfit, in Bengal, gave 8 * 3 per cent, of
>ta68ium nitrate, and 3*7 of calcium nitrate, or 12 per cent, of total
itrates. The soil around old buildings in the Punjaub is very pro-
kctire of nitre, which appears as an efflorescence, not to be confounded
ith the sodium sulphate crust occurring on the reh, or barren lands,
be deposit is scraped up as often as it is renewed, and submitted to
mple treatment for the separation of the nitre from the accompany-
ig dirt by the agency of watei* and filtration. A small spade is used
collecting the earth, which is taken off to a depth of 1 to 2 in. and
led in heaps 2 to 4 ft. high, where it is left without taking harm
U an opportunity arises for transporting it to a spot where water
bd fuel are available. In the upper part of the Punjaub, the extrac-
3n process is conducted in a series of wide-mouthed earthen pots,
ith an aperture in the base, supported on earthenware stands, so as
admit of placing cups beneath the pots. On the bottom of each
>t is spread a b^ of straw, covered with a layer of wood ashes ;
OTo this, the nitrous earth is added till it reaches nearly to the top
the pot. Then water is applied till all soluble salts contained in
« earth have been dissolveid and carried in solution into the cups
low. The straw bed acts mechanically as a filter to hold back in-
hble matters ; the wood ashes act chemically, affording potash in
i available fi[>rm, so that any calcium nitrate present may be con-
rrted into potassium nitrate, the nitric acid in the calcium nitrate
changing bases with the carbonic acid united to the potash in the
ood adbes. The very weak nitrous solution thus obtained is used
•tead of fr^sh water for washing through the contents of another
lies of pots, and thus becomes gradually charged with saltpetre to
le extent of 2 or 3 per cent.

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The next prooess is the removal of the water and orystaUisatk
of the salt. This is oonducted in elliptical iron dishes, measniia
1 or 2 ft. across and 6 to 9 in. deep, heated from beneath ; as eT«p
ration proceeds, fresh liquor is added, during a period of 12 to 1
hours. The scum which rises is skimmed o£f, and at a oertain poo
of concentration the crude potassium nitrate, with aooompanyii
saline impurities, is abundantly precipitated. This product in boa
districts is termed dkcmah^ and contains 45 to 70 per cent, of potassiii
nitrate. The small pans used in the Upper Punjaub give 8 to 16 1
of crude nitre per shift of 30 to 36 hours. Over 4000 pans are ks]
working in the Punjaub, In addition, there are over a dozen lai]
shallow basins, called aqar^ where sun-heat is utilised for evapon

In the different districts, slight modifications of the prooa
described above are in vogue. Thus, in Mooltan, the liquor, after i
to 24 hours boiling, is often run into a vat to cool for a night, and n«
morning the crystals are raked out and washed in a woollen cloii
being then tied up in it, and exposed to the sun till the moisture hi
been dissipated. Sometimes the filter is made on the ground in a
inclined situation, being formed with mud walls lined with stiff di
on three sides, the remaining side being left open for escape of tl
liquid, but provided with r^ds or closdy-woven grass mats, with <
without a Damboo false bottom; the liquid passes into a roeervo
made of packa masonry. In Ouzerat, the nitrous solution is passe
through a cloth filter ; it is evaporated to about one-fourth its boll
and on cooling affords an impure crystalline product {ik(ma\) worf
about 8«. per cwt.). When re-dissolved, filtered, and re-crystallise
forming Jcalmee^ it is worth 22«. The following table of the avei
cost per ton of Indian saltpetre is instructive : —

Prime cost of crude material at the fiioiory 4 2

Salaries, bags, packing, &c 1 14 2

Freights and expenses from factory to Bombay 5 17 3

Interest on outlay at 9 per cent 13 8

Government licence 2 7

Insurance at 7 per cent 17 1

13 6 9
Profit per ton 10 3

Selling price at a brisk demand at Bombay H 7

Indian, exports of saltpetre reach something like 25,000 Um
annually, with a value of over half a million sterling.

Nitrates of potash and lime are of frequent oocurrenoe in Cevl<a|
Some 30 places might be enumerated where saltpetre is produced ani
has been prepared for market. The formation of the mineral is ap
parently confined to caves in dolomitic rocks, the felspar in whiol
contributes the potash base.

An analysis of the most productive nitre rode near Doombera, il
an unfrequented cave, showed 2*4 per cent, potassium nitrate, ain
0*7 ])er cent, of magnesium nitrate. The nitre earth from the greaj
cave in Lower Ouva, near Wellaway, yields 3*5 per cent, of calciajii

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litraie, and 3*3 of potassinm nitrate. The nitre orop is harvested
Inriiig 6 months of the year by chipping off the iDomsted portions of
he avails of the caverns ; the fragments are reduced to powder, mixed
rith an eqoal portion of wood ashes, and dosed with water. The
wtaasinm nitrate present, as well as that produced from other nitrates
}7 the action of tne wood ashes, is dissolved by the water, and the
olution is evaj>orated first in pits exposed to the sun's rays, and then
the crystallising point in fire-heated pans.

In the government of Budokh, Thibet, saltpetre is obtained by
ligging np the soil, which is put into brass vessels, and treated with
lot water. The solution thus formed is decanted into another vessel,
nd there allowed to cool, that the nitre may crystallise out. By the
nide native method, one man can prepare a sheep load (say 20 lb.)
D 3 weeks.

Saltpetre abounds in Eastern Turkestan, especially in the hills
eyond Earshi (Neksheb), a large town 91 miles south-east of
k)khara. Here, previous to 1875, the Emir had a large powder
KJtory. Other factories existed in Khokan.

On the Bio das Yelhas, Brazil, saltpetre is found in quantities at
b Bonth-eastem side of the Serrote, in a series of caves. The process
f extracting the nitre from the chocolate-coloured earth is one of
xiviation. The earth is put into a bangue or strainer, generally
ansisting of a square pyramid of bockrding, with the base upwards,
lie poorer people use a hide, supported on four uprights. When
chansted with not water, the nitrous particles find their way, duly
Itered, through a tube leading to a cocke^ or trough, often a bit of
\d canoe. The decoaiay as it is now called, is a thin greenish liquid,
bich must be boiled in a tocAo, or metal pan, like that used for sugar.
\v^ ia^ko is sometimes mounted upon an ant-hill. The nitre is
lified by repeating the process, and assumes a yellowish-white

Potassium nitrate possesses a qualitv which distinguishes it from
idiom nitrate, and gives it a greater value, viz., that it is notably leas
ible to deUqueecenoe in the presence of a moist atmosphere. Its
lief use is in the manufacture of gunpowder and fireworks.

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«* Alkali linds," '* alkali dust," "alkali water," are familiar tern
indicating the presence of varioas sodium salts (bicarbonate, carbonat
chloride, and sulphate), as incrustations or in solution, and geneiaU
condemned as unmitigated evils by the agriculturist, but represeo
ing considerable mineral wealth when properly utilised.

Most prominent are the deserts and " sinks " (undrained lakes) <
the Oreat Basin of Western America. Here the salts are mixtures i
varying proportions of carbonate, chloride, and sulphate, carbonal

§nerally piedominating on the Western side, chloride in the oenti
reat Salt Lake), and sulphate on the Eastern side. Dr. T. 1!
latard* has made an interesting estimate of the carbonate of sod
contained in only three of the alkjtline lakes, based on his analyses i
the waters of these lakes, which give the following results stated i
grams to the liter : —






Fe,0, .. ..
A1,0, .. ..



!f°':: :: ::

H (in NaHCOa)

Albert Lake.





39 172

Mono Lake.


\ 0030


12 1036









If we unite these constituents into the combinations in whid^
for all practical purposes, they exist in the water, we shall get Uiea
figures: —

Silica (SiO,)

Iron and alnmina (Al,Fe,0,)
Oalcinm carbonate (OaCOg) ..
Magnesinm carbonate (MgOOg)
Sodinm borate (Na^B^O^r) . .
PotasBinm chloride (KOI) . .
Sodinm chloride (KaCl) . .
Sodinm snlpbate (Na^OJ ..
Sodinm carbonate (Na,CO|) ..
Sodium bicarbonate (NaHOO,)





















\ 055








* 'Mineral Industry/ i. 421.

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If we take the cub. ft. = 28 '32 lit, the lb. =453 '6 grm., the acre-
rat =43,560 cub. ft., and the areas and depths of the Gtkes, we shall
let for the amount of sodium carbonate and bicarbonate in these three
ikes alone the following surprising figures : —

Area and Depth.




fooo Lake

wens Lake









These are but three localities. They are the largest, but there
re many others. Of these the best known are the two lakes at
^gtown, Nevada, from which alkaline carbonates have been ex-
acted for many years, as is also the case in Long Valley, California,
[any of the smaller occurrences are near existing main lines of
^nsportation, and can be made feeders to centrally located refining
orks. The refining cost at such works must be less, and it should
»t no more to produce the crude material at small places than at
rger ones. The difference is the increased cost of transportation to
le refinery.

All the alkali on the western side of the Great Basin contains
dium carbonate and bicarbonate, and it is upon their property to
rm a C(»mpound more soluble than the bicarbonate but le^s so than
le carbonate that the method of extraction is founded. If we have
solation of the two salt*<, with or without sulphate or chloride, and
cpoee it to spontaneous evaporation, we shall, at a certain degree
^ concentration, get a crop of acicuLar crystals which have the
1 lowing composition : —

Snda (Na,0)
Carbonic acid (CO,)
Water (H,0)

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 39 of 76)