Charles George Warnford Lock.

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

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n£.tobes throughout.

^^ details of one of the borings are given in illustration of these
nciples. The hole was bored 14 in. diam. to a depth of 326 ft., and


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was lined with a 13-in. iron pipe, below which point it was redtioec
to 12| in. down to 500 ft., when a diameter of 8j^ in. was adopted fo
the remaining 960 ft. A lower impure division of the salt-bed wa
then shut off by a packing of sand and concrete, after which a wood^

rking was put into the hole immediately above the bed intended t
worked, and the hole was lined for a length of 16 ft. with ooo
orete, or to within 2j^ ft. of the lower end of the lining-tnbe, whic
space was made secure by concrete put down the hole, in order to ge
a tight joint. In every case the hole was filled with concrete, whie
was allowed to set until it was sufficiently hard for reboring. Th
protection of the sides of the hole from erosion by the descendin]
current of water was effected, in the lower portion, of B^ in. diam.,lr
copper lining-tubes of 7^ and 7 in. bore, made in lengths of 10 ft
which were jointed by coupling-pieces 8 in. long, and secured b
riveting and brazing. At the top they were strengthened by a br»
collar, If in. thick, which lay in the shoulder formed by tiie o£te
fix)m the smaller to the larger diameter at the depth of 500 ft. Th
lining of the upper section, in wood, is 10 in. diam. and 1 in. thic
for the first 500 ft, being in oak tubing, built up like a cask of staTa
10 ft in length ; the remainder is in pine, bored out from the tmiib
of carefully selected trees. The brine-lifting pumps are made <
brass and copper tubes, whose diameter admits a space of about 2 u
within the Uning-tubes for the introduction of the dissolving coircii
of fresh water. This gives a length of about 100 ft. above the £n
level of the brine column, which in its turn is dependent upon th
magnitude of the fresh-water column. The suction column, i. e. tk
position of the foot valve of the pump barrel, is determined by tl
densitv of the brine. The worUng barrel of the pump is made 1
time the diameter of the suction pipe, and the suction pipe about \ s
larger than the latter dimension, so that the pump bucket may 1
easily withdrawn for repairs when required. When these dimensai
have been fixed, the weight of the pump is calculated approximate!]
and that of the column of brine above the valve accurately, in oid
to determine the necessary substance of the copper tubes and bn
collars, which are so chosen as to be subjected to a working strain y
one-fourth of the ultimate resistance. The screw collars of the suotifl
pipes are 5 in. and those of the rising pipes 7*8 in. external dian
the breadth of the annular space for tne introduction of the woridi
current of fresh water is therefore 1 in. in the lower and 1 * 2 iiL i
the upper part of the hole.

The results obtained from these borings have not quite fdlfiUe
the expectations of their projectors. A tolerably pure and stro^
brine, containing 24j^ to 25 per cent, of salt, has been obtained fra
some of the bore*holes, while others only average 21 per cent., •■
some are often muddy. Experience seems to show that the yield i
dependent more upon peculiarities in the bed of salt, than on d
power of the pumping machinery ; and that in order to obtain ban
at a maximum of concentration, the pumping must not exceed a ori
tain speed. This maximum has been attained in a well which yiflN
per minute an average of about 4 cub. ft. of brine, containing 18*ifl
of salt per foot, mien pumped at a more rapid rate tiie brioB 1
weaker, and not so well suited for boiling down.

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The brine as ptunped needs further treatment to yield its salt. In
ills oonneclion the reader may be reminded that most of the sub-
itanoes designated saline are more soluble in hot than in cold water.
rhe ordinary way of obtaining such bodies in the crystalline form, a
)rooe88 employed to free them from any impurities they may contain,
oluble as well as insoluble, is first to make a saturated solution in
tot water. This is allowed to cool, when the difference in the
[oantily capable of being dissolved in hot water and in cold is
epoflited in the form of crystals. The crystals, so obtained, usually
ontain varying quantities of solidified water, known as the water of

Gonimon salt is one of the few exceptions to the law of relative
[»lubility just named, for it is taken up almost as largely by cold
rater as by hot. It possesses the further peculiarity of forming
rystals freia from water of crystallisation. The former property
mders an entirely different process necessary for obtaining it in the
rystalline form to that usually pursued in such cases. The brine as

is delivered from the wells, is run into a large reservoir, where any
Lithy matter held in suspension is allowed to settle to the bottom,
he dear solution is then run into pans, 60 ft. long, 20 ft. wide,
id 2 ft. deep. Heat is applied at one end by the combustion of
[lali coed, beyond which longitudinal walls, which serve to support
le pan and distribute the heat, conduct the products of combustion
) tne &rther extremity, where they escape into the chimney at a
mperature of 600° to 700° F. On the surface of the heated brine,
hich for salt intended for the soda-makers is kept at about 196° F.,
mute cubical crystals speedily form. On the upper surface of these
her small cubes of salt arrange themselves, in such a way that in
e coarse of time there will be a small, hollow inverted pyramid of
ystalliBed salt. This ultimately sinks to the bottom, where other
lall crystals unite with it, so that the ultimate shape frequently
oomies completely cubical. Every second day the salt is '' fished "
f, and laid on drainers to permit the adhering brine to run back
to the pans.

This process of evaporation appears very simple, but for its proper
rformanoe certain precautions are required. If the water admitted
G the brine-well contains vegetable substances, a fine covering,
[isisting of salt and this extractive matter, forms a pellicle on the
riaoe of the brine which completely stops evaporation, and, as a
^sequence, the generation of crystals.

For the production of table-salt, the boiling is carried on much
»re rapidly, and at a higher temperature (226 F.) than for chemical
t- The crystals are very minute, and adhere together by the*
idification of the adhering brine, effected by exposure on heated
e& Tlie loaves so obtained require to be pounded, and then a^ord
> fine table-salt in common use. For fishery purposes, the crystals
\ pireferred very coarse in point of size, and to produce these the
fcporating process is conduct^ at a still lower temperature (100° to
irFS) and much more slowly than when salt for the soda-makers is

As already mentioned, the usual mode of evaporating the brine is

z 2

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by means of coal burned under the salt-pans. At the Clarence Iron-
works more gas escaped from the blast- furnaces than was required for
heating the air and raising steam. The extent of this excess ha?ing
been ascertained, large pans were placed over properly constructed
flues immediately behind the steam-boilers. From these, by means of
the waste heat, about 200 or 300 tons per week of salt is obtained.
At Winsford, Blagg has introduced hot air to the fires, and finds that
he can dispense with half his fireplaces, saving fuel and labour, and
obviating the discharge of black smoke.

In the mode of evaporating the water by open pans, the amonnt
of fuel used is large. Even when the brine is very strong, 3 tim«i
the amount of water has to be evaporated as compared ¥dth tk
amount of salt raised, and when the solution is weaker, of course tk
proportion of water evaporated is still greater. In some apparatis
for evaporating from salt water, in order to get distilled water i<A
drinking purposes, is obtained as high an evaporation as 27 lb. cl
water for 1 lb. of coal burned, and with another apparatus as much ai
45 lb. of water per 1 lb. of coal, which is perhaps 10 times as high «a
the evaporation obtained by the open-pan process. In the one case il
is the water which is required, the salt being thrown away, while ii
the other case it is the salt that is needed, and the water is thron
away ; but the same plant is applicable for both purposes.

!m all ordinary pans the salt forms in the hot brine, while ^
evaporation goes on, and falls on the plates which form the bott^
From time to time the salt is removed by rakes and shovels, but som^
salt or "pan-scale'* is always lying on the bottom, impeding thf
action of the fire, and by shutting in the heat causing the iron pktd
to bend and bum. A constant strain and destructive action is tha
at work, and it is no matter of surprise that the pans often leall
About once a week they are " dodged " or beaten with hammeis u^
crow-bars in order to loa'^en and remove the hard pan-soale whid
adheres to the plates. After this operation, leakages are more £n
quent. The effect of leakage is that brine dries upon the fire or th|
heated brickwork below, and it there forms large blocks of stli
Some of this is volatilised as salt vapour and carried away in th
smoke, or it is decomposed by the silica of the hot bricks, and also n
the sulphurous acid of the coal smoke. When a salt-pan leaks, thei^
fore, the smoke from the chimney connected with it may contaa
besides the ordinary coal smoke, and its accompanying suli^nnii
acid arising from the pyrites in the coal, the vapour of votatilis^
salt, hydrochloric acid and steam. These facts must be borne in mii^
when establishing a salt-pan in populous districts, and due proviaM
be made.

For additional information on salt-pans, the reader is referrei
Spons' EncyclopaBdia of Manufactures, art. " Salt."

1 he yearly output of salt in England is about 2,000,000
value 1,000,000/,

In India, the manufacture of salt from the ocean, in puis, eil
by solar or artificial evaporation, has been carried on since very ei
times, in various districts and regions which are adjacent to the oo
The industry is restricted to Eutch, portions of Madras, Bombay,

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provinoe of Orissa, in Bengal, and parts of Burma. The artificially
er-aporated salt, though of distinctly purer character than that which
is produced by the heat of the sun, is not used by the stricter Hindus,
M they regard it as having been cooked, and therefore impure.

The Bunn of Eutch is a large sandy desert for 9 months in the
^oar, and durine the remaining 3 is nearly covered by the waters
from the Gulf 01 Eutch, when it becomes a muddy swamp. Below
^Toand, in some places, very strong brine is met with, and this, when
properly treated, produces excellent salt. The apparatus used for
mising the brine is very primitive, and merely consists of a long teak
RX)od pole, tied at about a fourth of its length to a post which is stuck
n the ground. To the shorter end of the pole is affixed a bcdance
weight, formed of a lump of mud, bound to the pole with coir-line.
To the lighter and longer end of the pole is attached a thin rope, and

this is slung an earthenware pot. These machines are generally
rected in pairs. A hole in the ground having been dug, the work-
aan pnlls down the ehaUy^ or earthen pot, into the brine at the
ottom of the hole, the depth of which is 8-12 ft. When the chatty

1 foil, the man allows it to ascend by means of the balance-weight,
nd empties the contents into a small channel, formed of earth, a little
bove the eur&ce of the ground. This channel leads the brine into
ana for evaporation by the heat of the sun. The pans consist merely
fa rectangular piece of ground, perhaps 200 ft long by 100 ft. wide,
nciosed by ridges of earth 1 ft. high. This process of evaporation
Dd continued supply of brine is carried on until the contents of the
ftns are reduced to a mass of beautiful large white crystals, some of
^hich are 1 in. diam.

The soil of many parts of India is largely charged with a variety
r salts, the concentration of which has resulted from a high degree
ratmoepberic evaporation, unaccompanied by subsoil drainage. The
ITect of irrigation on such lands, even with the pure water of the
an^es canal, has, in not a few cases, produced sterility in a manner
hich admits of a very simple, though not at first sight obvious
Eplanation. It is that the general level of the highly saline subsoil
ateis has been raised to a level where they can act prejudicially by
le deposition of the efflorescent salts, collectively called reh. The
reparation of salt by lixiviation of such saline earths, though once
rgely practised, is now nearly extinct.

Saline springs and wells are very abundant in parts of Assam,
urraa, and the Punjab. As in other parts of the world, they fre-
lently occur in conjunction with petroleum springs. Wells have
»en need in many parts of India to extract the above natural subsoil
iline -waters, from which very large quantities of salt have been, and
ill are, manufactured.

There are also in India some notable examples of lakes which,
ivin^ more or less extensive drainage basins but no outlets, deposit
It when, during the heat and drought of summer, the limit of
titration is passed. The principal of these lakes are situated in Baj-
itana, and among them the Sambhar Lake is the most important The
aaniiftctare of salt, since it came into British hands, has been largely
ivdcped, and the total annual outturn now exceeds 100,000 tons.

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In the Punjab are two distinot geologioal formations, wUd^
include deposits of rock-salt of enormous extent. One of these^
believed to be of Silurian age, is situated in the salt range on bot)^
sides of the Indus, while the other, of probably Eocene age, lieri
wholly trans-Indus in the district of Eohat The former is worked
by means of mines, and the latter by open quarries. The produce ol
both is sold locally.

The manufacture of salt, which has been carried on in China for i
period of nearly 2000 years, is conducted somewhat as follows. B^
means of a rude iron drill, holes 6 in. diam. and varying from a fe^
score of feet to 6000 ft. or 6000 ft. in depth, are bored in the rodt
The boring is sometimes continued for 40 years before brine is reached^
and is carried on from generation to generation. When brine ii
finally found, it is drawn up by bullocks in long bamboo tubes b^
means of a rope working over a huge drum. In the vicinity of Uk
salt wells, natural gas wells are also found, from which gas is supplied
to evaporate the bnne in large iron cauldrons, leaving the salt as i
deposit. The product in some districts is enormous. There are Vi
gas weUs and about 1000 brine wells now in operation, producing
annually 200,000 tons of salt, valued at about 1,000,000L

The United States possess enormous salt deposits. The salt field
at Petite Anse, Louisiana, is about 150 acres in extent, 16 to 25 ft
below the ground, somewhat triangular in shape, and, so far as known,
2500 to 2600 ft. wide. From borings made with a diamond drill some
4 years ago, it was learned that this bed is over 1000 ft thick. hX
this depth the borings were discontinued. The most singular fad
about this salt deposit is that it stands, so to say, on its edge. Thf
stratification is nearly perpendicular from east to west, indicating an
upheaval, and what was its original depth is now its width. It is al
present considered to belong to the Tertiary period, though perhapc
its true position can only be known with certainty when the under-
lying formation is reached. The salt occurs as a solid crystalline rod[
of a saccharoidal texture, the individual crystals being indistinctlj
aggregated and interspersed with microscopic crystals of gypsum.
This salt is very pure, and if it were not for the peculiarity that it
" cakes " after being ground, it would years ago have had a muc^
greater and more extended market, especially as a table salt.

The method of mining is peculiar, and consists of a series ol
galleries. The galleries of the second level are run 80 ft in width
and 45 ft. high, leaving supporting pillars 60 ft. diam. The lowes
pillars are so left that the weight of the upper ones rests upon tiiem
in part, if not wholly, with a thickness of at least 25 ft of salt-rock
between. There are 16 to 25 ft. of earth above the salt-deposit The
contour of the latter conforms nearly with that of the sur&ce. The
working-shaft is 168 ft deep. The depth to the first level or floor k
90 ft ; to the second, 70 ft farther. The remaining 8 ft are used fur
a dump. The galleries of the first level were run, on an average
40 ft. in width and 25 ft. and upwards high, leaving supporting pilltfi
40 ft diam. The galleries cross each other at right angles, and tbi
ground-plan strongly resembles a chess-board.

In running a gallery, the first work is the " undercutting" on th«

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level of the floor, of snffioient height to enable the miners to work with
BMe. The salt is then blasted down from the overhanging body. The
jreariy ontpnt is about 50,000 tons.

The salt as it comes from the mine is dumped into corragated oast-
LTcm rolls, which crush it. Next it goes into revolving screens, which
take out the coarser lumps for '* crushed salt," and let the fine stuff
paas to buhr stones. These grind the salt, and from them it goes to
pneumatic separators, which take out the dust, and separate the
narket salt into various grades. Taking the dust out is essential to
:he production of a salt that will not hat Sen, since the fine particles of
lust deliquesce readily, and on drying cement the coarse particles
together. The drill used in the mine is what is known as the
' Bussian auger." It is turned by hand and forced by a screw of 12
hreadfl per inch. The holes take cartridges 1^ in. diam.; 2 men will
XWB 76 ft. of hole per working day of 8 hours ; j lb. of 18 per cent,
lynamite is used per ton of salt mined.

The salt found at Retsof, New York, when taken from the shafte,
B of a grey colour, due to the presence of finely disseminated dark
;rey clay, which, on solution of the salt, sinks, leaving a perfectly
lear brine above. The salt is mainly an aggregation of not quite
lerfeotly developed crystals, and when the lumps are broken the
leavage of many of these cxystals is very marked ; the fracture is
oDchoidal. Large pieces of the salt show stratification.

This rock-salt bed is in Upper Silurian. It extends east and west,
ccording to our present knowledge, from Madison County to Lake
Srie, and north and south from Le Koy to Castile. The salt stratum
I over 100 ft. thick. In one well below the Tully Hills, Onondaga
buntj, it had a thickness of 310 ft., and in another well 228 ft.
t extends under Lake Erie, and underlies the northern counties of
>hio and Indiana, the entire peninsula of Michigan, and the western
art of the Province of Ontario along Lake Huron and the St. Clair
iver. In some parts of this salt deposit — underlying thousands of
|uare miles — ^we find the salt occurring in one vein, or even in seven
eins, with layers of shales or clay between them of varying thick-
ess, and at different depths below the surface. The phenomena are
(plained by events at any of the large salt lakes covering many
ondred miles of surface. During the hot summer months evaporation
; greatly in excess of the water entering the lake. As evaporation
rogr^sses, the less soluble salt, viz. tiie lime sulphate, separates
ret from the water as gypsum, forming a layer over last year's deposit,
rUowed, as soon as the point of saturation of the salt is reached, by
le latter in the form of a deposit, which will continue to increase
ith the advancing evaporation until a change in the weather takes
laoe. When rain-water descends in large quantities from the sur-
nmding hills, carrying all the loose material in its way into the
raally dried-up streams and brooks, they in turn discharge water
eavily laden with mud into the lake. The heavier material settles
eareat to the lake shore on the lately deposited salt, forming a more
r leoB thick layer, which in time hardens to shale or marl, while the
ghter, mechanically suspended particles are carried farther out into
!ie lake, according to the force of the incoming waters. They also

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finally settle, forming a much thinner layer. Some parts of the lake,
if it is a very large one, may not be reached by the suspended matter,
and there no sediment is formed over the salt below. Since the rain-
water is mnch lighter than the saturated brine of the lake, they mix
but slowly, the fresh water flowing over the brine. Heavy froBts
occur, and soon a strong crust of ice covers the surface of the entire
lake. With the returning warm weather, rains again set in, canyiiig
a fresh load of loose material toward and on to the ice of the lake*
where the ice keeps it from sinking to the bottom until it becomes too
weak to bear the load, and then both disappear below the sur&ce
Thus also considerable quantities of this debris may be carried by th«
floating ice into places where there was none before. Evaporation, in
consequence of the elevated temperature and the ever-moving air, soos
causes the lake water to become saturated with lime sulphate, whicli
it dissolves from the soil and suspended material. It separates, form-
ing a new layer over the bottom of the lake in the form of gjrpsom,
to be followed by another layer of salt again as evaporation progresseiy
and so the process goes on.

There are at present 4 salt shafts in Kansas — ^two at Eingmao,
one at Lyons, and one at Eanopolis — ^with a daily capacity of abcn^
2000 tons. Thus the United States now have 9 salt shafts, with a
total capacity of 4500 tons a day. The average Kansas rock salt does
not di£fer materially in appearance from the New York rock salt
Geologically this salt deposit is found at the base of the Triaasie.

The great bulk of American sea salt is obtained in California, in
the Bay of San Francisco, especially in the county of Alameda, when
there are at present over 25 worlu. In Los Angeles and Scm Diego
counties, bordering on the Pacific, there are also several works in
which sea salt is produced. It is all used for home consumption.

The most important salt lake in the United States is the Great
Salt Lake of Utah, which is 75 miles long by 30 miles wide. THe
water is said to contain about 20 percent, of pure salt and 2 per cent
of other saline matters.

The brines of the United States which serve to-day for the maniH
fiacture of most of the salt used for domestic purposes are dintribatei
over a very large territory, and oocur in several geological formationir
from the Silurian upward. As they come from the bowels of tha
earth they are often highly charged with carbonic acid gas, and ia
consequence contain traces of iron bicarbonate and sometimes of lime,
both of which will separate almost entirely as soon as the free car*
bonic acid, the solvent, has escaped, and the iron has become oxidised
Other brines are often charged with carburetted hydrogen to such aa
extent that the gas has been used as a fuel for their evaporatioB.
Petroleum is found associated with some brines. Among the othff
impurities, lime sulphate (gypsum) is the most important, since it
prevents the continuous manufacture of salt by artificial heat in oob-
sequence of its tendency to bake on highly heated surfaces, forming a
constantly increasing coating over them. This coating adheres wit^
such tenacity that it is impossible to remove it sufficiently while the
works are in operation. Being a very bad conductor of heat, it
entails a great expenditure of fuel if the operation is continued

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lejond a certain time ; henoe the necessity oi interraptiiig the pro-
ess to remove these scales. Several methods have been proposed to
precipitate the lime sulphate from the brine before the salt separates,
ither by snperheatinff the brine or by chemical means ; but thus far
he expense incorred bv these methods has been out of proportion to
he benefits derived ; hence the practical removal of lime sulphate
rom salt brines is even now the most important problem in connection
rith the manufacture of salt by artificial heat.

The manufacture of salt from brines by solar evaporation is carried

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 38 of 76)