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SALT (a common Teutonic word, cf. Dut...

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Originally appearing in Volume V24, Page 90 of the 1911 Encyclopedia Britannica.
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SALT (a See also:common See also:Teutonic word, cf. Dutch zout, Ger. Salz, Scand. salt; cognate with Gr. &Xs, See also:Lat. sal)  . In See also:chemistry the See also:term See also:salt is given to a See also:compound formed by substituting the See also:hydrogen of an See also:acid by a See also:metal or a See also:radical acting as a metal, or, what comes to the same thing, by eliminating the elements of See also:water between an acid and a See also:base (see ACID; CHEMISTRY) . See also:Common Salt . Common salt, or simply salt, is the name given to the native and See also:industrial forms of See also:sodium chloride, NaCl . Pure sodium chloride, which may be obtained by passing hydrochloric acid See also:gas into a saturated See also:solution of the commercial salt, whereupon it is precipitated, forms colourless, crystalline cubes (see also below under See also:Rock salt) which melt at 815.4°, and begins to volatilize at slightly higher temperatures . It is readily soluble in water, See also:loo parts of which dissolve 35.52 parts at o° and 39.16 parts at loo° . The saturated solution at 109.7° contains 40.35 parts of salt to loo of water . On cooling a saturated solution to -1o°, or by cooling a solution in hot hydrochloric acid, the See also:hydrate NaCl . 2HZO separates; on further cooling an aqueous solution to -20° a cryohydrate containing 23.7% of the salt is deposited . The See also:consideration of this important substance falls under two heads, See also:relating respectively to See also:sea salt or " See also:bay " salt and " rock " salt or See also:mineral salt . The one is probably derived from the other, most rock salt deposits bearing See also:evidence of having been formed by the evaporation of lakes or seas . Sea Salt.—Assuming that each See also:gallon of sea water contains 0.2547 lb of salt, and allowing an See also:average See also:density 2.24 for rock-salt, it has been computed that the entire ocean if dried up would yield no less than four and a See also:half million cubic See also:miles of rock-salt, or about fourteen and a half times the bulk of the entire See also:continent of See also:Europe above high-water See also:mark .

The proportion of sodium chloride in the water of the ocean, where it is mixed with small quantities of other salts, is on the average about 3.33%, ranging from 2.9% for the polar seas to 3.55% or more at the See also:

equator . Enclosed seas, such as the Mediterranean, the Red Sea. the See also:Black Sea, the Dead Sea, the See also:Caspian and others, are dependent of course for the proportion and quality of their saline See also:matter on See also:local circumstances (see OCEAN) . At one See also:time almost the whole of the salt in See also:commerce was produced from the evaporation of sea water, and indeed salt so made still forms a See also:staple commodity in many countries possessing a seaboard, especially those where the See also:climate is dry and the summer of See also:long duration . In See also:Portugal there are salt See also:works at See also:Setubal, Alcacer do Sal, Figueira and See also:Aveiro . See also:Spain has salt works at the Bay of See also:Cadiz, the Balearic Islands, &c.; See also:Italy at See also:Sicily, See also:Naples, See also:Tuscany and See also:Sardinia . See also:France has its " marais salants du midi " and also works on the See also:Atlantic seaboard; whilst See also:Austria has " Salzgarten " at various places on the Adriatic (Sabbioncello, See also:Trieste, See also:Pirano, See also:Capo d'See also:Istria,&c.) . In See also:England and See also:Scotland the See also:industry has greatly fallen off under the competition of the rock-salt works of See also:Cheshire . The See also:process of the spontaneous evaporation of sea water was studied by Usiglio on Mediterranean water at See also:Cette . The density at first was 1.02 . Primarily but a slight See also:deposit is formed (none until the concentration arrives at specific gravity 1.0509), this deposit consisting for the most See also:part of See also:calcium carbonate and ferric See also:oxide . This goes on till a density of 1.1315 is attained, when hydrated calcium sulphate begins to deposit, and continues till specific gravity 1.2646 is reached . At a density of 1.218 the deposit becomes augmented by sodium chloride, which goes down mixed with a little See also:magnesium chloride and sulphate .

At specific gravity 1.2461 a little sodium bromide has begun also to deposit . At specific gravity 1'311 the See also:

volume of the water contained- - Magnesium sulphate . 11.45 °/ Magnesium chloride . 19.53 °A, Sodium chloride .. 15-98% Sodium bromide .. 2'04% See also:Potassium chloride 3.3o% Up to the time then that the water became concentrated to specific gravity 1.218 only o• 150 of deposit had formed, and that chiefly composed of See also:lime and See also:iron, but between specific gravity 1.218 and 1.313 there is deposited a mixture of Calcium sulphate . . . . 0'0283% Magnesium sulphate . . . o.o624 % Magnesium chloride . . 0.0153 % Sodium chloride .. . 2.7107 % Sodium bromide . . 0.0222 % 2.8389 % Of this about 95 % is sodium chloride .

Up to this point the separation of the salts has taken See also:

place in a fairly See also:regular manner, but now the temperature begins to exert an See also:influence, and some of the salts deposited in the See also:cold of the See also:night dissolve again partially in the See also:heat of the See also:day . By night the liquor gives nearly pure magnesium sulphate; in the day the same sulphate mixed with sodium and potassium chlorides is deposited . The See also:mother-liquor now falls to a specific gravity of 1.3082 to 1.2965, and yields a very mixed deposit of magnesium bromide and chloride, potassium chloride and magnesium sulphate, with the See also:double magnesium and potassium sulphate, corresponding to the kainite of See also:Stassfurt . There is also deposited a double magnesium and potassium chloride, similar to the carnallite of Stassfurt, and finally the mother-liquor, which has now again risen to specific gravity 1.3374, contains only pure magnesium chloride . The application of these results to the See also:production of salt from sea water is obvious . A large piece of See also:land, barely above high-water mark, is levelled, and if necessary puddled with See also:clay . In tidal seas a " jas " (or storage See also:reservoir) is constructed alongside, similarly rendered impervious, in which the water is allowed to See also:settle and concentrate to a certain extent . In non-tidal seas this storage See also:basin is not required . The prepared land is partitioned off into large basins (adernes or muants) and others (called in France aires, suillets or tables salantes) which get smaller and more shallow in proportion as they are intended to receive the water as it becomes more and more concentrated, just sufficient fall being allowed from one set of basins to the other to cause the water to flow slowly through them . The flow is often assisted by pumping . The sea salt thus made is collected into small heaps on the paths around the basins or the floors of the basins themselves, and here it under-goes a first partial See also:purification, the more deliquescent salts (especially the magnesium chloride) being allowed to drain away . From these heaps it is collected into larger ones, where it drains further, and becomes more purified .

The salt is collected from the See also:

surface by means of a sort of wooden See also:scoop or scraper, but in spite of every precaution some of the See also:soil on which it is produced is inevitably taken up with it, communicating a red or See also:grey tint . Generally speaking this salt, which may contain up to 15% of impurities, goes into commerce just as it is, but in some cases it is taken first to the refinery, where it either is simply washed and then See also:stove-dried before being sent out, or is dissolved in fresh water and then boiled down and crystallized like See also:white salt from rock-salt brine . The salt of the " seines du midi " of the See also:south-See also:east of France is far purer, containing about 5% of impurities . In See also:northern See also:Russia and in See also:Siberia sea water is concentrated by freezing, the See also:ice which separates containing little salt; the brine is then boiled down when an impure sea salt is deposited . Rock-salt.—To mineralogists rock-salt is often known as halite—a name suggested in 1847 by E . F . Glocker from the See also:Greek &Xs (salt) . The word halite, however, is sometimes used not only for the See also:species rock-salt but as a See also:group-name to include a See also:series of haloid minerals, of which that species is the type . Halite or rock-salt crystallizes in the cubic See also:system, usually in cubes, rarely in octahedra; the cubes being solid, unlike the See also:skeleton-cubes obtained by rapid evaporation of brine . The mineral has perfect cubic cleavage . Percussion-figures, readily made on the cleavage-faces, have rays parallel to faces of the rhombic See also:dodecahedron; whilst figures etched with water represent the four-faced See also:cube . Rock-salt commonly occurs in cleavable masses, or sometimes in laminar, granular or fibrous forms, the finely fibrous variety being known as " See also:hair-salt." The hardness is 2 to 2.5 and the spec. See also:gray.2.1 to 2.6 .

Rock-salt when pure is colourless and transparent, but is usually red or See also:

brown by See also:mechanical admixture with ferric oxide or hydroxide . The salt is often grey, through bituminous matter or other impurity, and rarely See also:green, See also:blue or See also:violet . The blue See also:colour, which disappears on See also:heating or dissolving the salt, has been variously ascribed to the presence of sodium subchloride, sodium, See also:sulphur or of a certain compound of iron, or again to the existence of See also:minute cavities with parallel walls . Halite occasionally exhibits double See also:refraction, perhaps due to natural pressure, It is remarkably diathermanous, or capable of transmitting heat-rays, and has therefore been used in certain See also:physical investigations . Pure halite consists only of sodium chloride, but salt usually contains certain magnesium compounds rendering it deliquescent . Minute vesicular cavities are not infrequently See also:present, sometimes as negative cubes, and these may contain saline solutions or See also:carbon dioxide or gaseous See also:hydrocarbons . Some salt decrepitates on solution (Knislersalz), the phenomenon being due to the See also:escape of condensed gases . Halite may occur as a sublimate on See also:lava, as at See also:Vesuvius and some other volcanoes, where it is generally associated with potassium chloride; but its usual mode of occurrence is in bedded deposits, often lenticular, and sometimes of See also:great thickness . The salt is commonly associated with See also:gypsum, often also with See also:anhydrite, and occasionally with See also:sylvite, carnallite and other minerals containing potassium and magnesium . Deposits of rock-salt have evidently been formed by the evaporation of salt water, probably in areas of inland drainage or enclosed basins, like the Dead Sea and the Great Salt See also:Lake of See also:Utah, or perhaps in some cases in an See also:arm of the sea partially cut off, like the Kara Bughaz, which forms a natural salt-See also:pan on the east See also:side of the Caspian . Such beds of salt are found in strata of very varied See also:geological See also:age; the Salt Range of the See also:Punjab, for instance, is probably of See also:Cambrian age, while, the famous salt-deposits of See also:Wieliczka, near See also:Cracow, have been referred to the See also:Pliocene See also:period . In many parts of the See also:world, including the See also:British See also:area, the Triassic age offered conditions especially favourable for the formation of large salt-deposits .

In England extensive deposits of rock-salt are found near the base of the See also:

Keuper See also:marl, especially in Cheshire . The mineral occurs generally in lenticular deposits, which may reach a thickness of more than too ft.; but it is See also:mined only to a limited extent, most of the salt being obtained from brine springs and See also:wells which derive their saline See also:character from deposits of salts . Much salt is obtained from See also:north See also:Lancashire, as also from the brine pits of See also:Staffordshire, See also:Worcestershire, See also:Yorkshire, See also:Durham and the Isle of See also:Man (Point of Ayre) . The salt of N.E . Yorkshire and S . Durham is regarded by some authorities as See also:Permian, but that near See also:Carrickfergus in Co . See also:Antrim, See also:Ireland, is undoubtedly of Triassic age . The Antrim salt was discovered in 185o during a See also:search for See also:coal: one of the beds at Duncrue mine has a thickness of 8o ft . Important deposits of rock-salt occur in the Keuper at See also:Berchtesgaden, in the Bavarian See also:Alps; at See also:Hall in See also:Tirol and at Hallein, See also:Hallstatt, Ischl and Aussee in the See also:Salzkammergut in Austria . Salt occurs in the See also:Muschelkalk at Friedrichshall and some other localities in See also:Wurttemberg and Thuringia; and in the See also:Bunter at See also:Schoningen near See also:Brunswick . The Permian system (Zechstein) yields the great salt-deposits worked at Stassfurt and at See also:Halle in Prussian See also:Saxony . The Stassfurt deposits are of See also:special importance for the See also:sake of the associated salts of potassium and magnesium, such as carnallite and kainite .

These deposits, in addition to having a high commercial importance, present certain problems which have received much See also:

attention, more particularly at the hands of See also:van't Hoff and his collaborators, whose results are embodied in his Zur Bildung der ozeanischen Salzablagerungen, vol. i . (1905), vol. ii . (1909) . (A See also:summary is given in A . W . See also:Stewart, See also:Recent Advances in Physical and Inorganic Chemistry, 1909; see also van't Hoff, Lectures on Theoretical and Physical Chemistry, vol. i.) A typical See also:section is as follows: Beneath the surface soil of See also:sandstone there is a layer up to loo ft. in thickness of carnallite, MgC12•KC1.6H2O, mixed with a little salt; this is followed by a thicker deposit of kieserite, MgSO9•See also:H2O, containing rather more salt than the upper See also:bed . Deeper down there are successively strata of polyhalite, MgSOi.K2SO4.2CaSO4.2H2O, and anhydrite, CaSO4, interspersed with regular layers of rock-salt; whilst below the anhydrite we have the See also:main rock-salt deposits . A bed of rock-salt in the Zechstein at Sperenberg near See also:Berlin has been proved by See also:boring to have a thickness of upwards of 4000 ft . The salt of Bex in See also:Switzerland is See also:Jurassic, whilst Cretaceous salt occurs in See also:Westphalia and See also:Algiers . Important deposits of salt are See also:developed in many parts of the See also:Tertiary strata . At See also:Cardona, near See also:Barcelona, Tertiary salt forms See also:hill-masses, while the Carpathian sandstone in See also:Galicia and Transylvania is See also:rich in salt . The extensive mines at Wieliczka are in this rock-salt, as also is the salt of Kalusz in Galicia, which is associated with sylvite, KC1 .

In North See also:

America salt is widely distributed at various geological horizons . In New See also:York it occurs in the See also:Salina beds of the See also:Onondaga series, of See also:Silurian age; and Silurian salt is found also in parts of See also:Michigan and in See also:Ontario, See also:Canada . Some of the salt of Michigan is regarded as Carboniferous . Rock-salt is mined in several states, as New York, See also:Kansas and See also:Louisiana; but See also:American salt is mostly obtained from brine . Deposits of salt, regarded as either Cretaceous or Tertiary, occur in the See also:island of Petite Anse, See also:west of See also:Vermilion Bay, in Louisiana . Salt often occurs in association with See also:petroleum and natural gas, and extensive beds were discovered in the See also:Wyoming valley in boring for petroleum . In the dry regions of the West salt occurs as an incrustation on the surface of the soil—a mode of occurrence found in See also:desert areas in various parts of the world . Cubic pseudomorphs representing rock-salt are sometimes seen in strata which have been deposited in shallow water, especially on the margin of a salt-lake . The salt has been dissolved out of its See also:original See also:matrix, and the cavity so formed has then been filled with See also:fine clayey or other mineral matter, forming a cubic See also:cast . Such casts are not infrequent in the Keuper marls and sandstones, and in the Purbeck beds of England . Manufacture.—The See also:chief centres of manufacture in England are at See also:Northwich, See also:Middlewich, See also:Winsford and See also:Sandbach in Cheshire, See also:Weston-on-See also:Trent in Staffordshire, Stoke See also:Prior and See also:Droitwich in Worcestershire and See also:Middlesbrough in Yorkshire.' The Cheshire and Worcestershire salt deposits are by far the most important . Although brine springs have been known to exist in both these counties ever since the See also:Roman occupation, and salt had been made there from time immemorial, it was not till 167o that rock-salt about 30 yds. thick was discovered at Marbury near Northwich by some men exploring for coal, at a See also:depth of 34 yds .

In 1779 three beds of rock-salt were discovered at Lawton, separated from one another by layers of indurated clay . The old See also:

Marston or Marston Rock mine is the largest and perhaps the See also:oldest in England . It was worked for about a See also:hundred years in only its upper bed, but in 1781, after traversing a layer of indurated clay intersected with small See also:veins of salt 10k yds. thick, a layer of rock-salt 33 to 37 yds. thick was found . Beneath it are others, but they are thin and impure . The See also:total depth of the mine to the bottom of the See also:lower level is 120 yds . At Winsford, where the same formation seems to recur, it is 159 yds. from the surface . The Marston mine covers an area of about 40 acres . The salt is first reached at 35-40 yds. in the Northwich See also:district, and the upper layer is 25-50 yds. in thickness (Marston 23-26 yds.); it has above its apparently lying in the recesses of its surface, a layer of saturated brine . This is the brine which is raised at the various pumping stations in Northwich and elsewhere around, and which serves to produce white salt . The beds are reached by sinking through the See also:clays and variegated marls typical of this formation . The salt is blasted out with See also:gunpowder . The Middlesbrough deposit was discovered by Bolckow and See also:Vaughan in boring for water in 1862 at a depth of 400 yds., but was not utilized, and was again found by Messrs See also:Bell See also:Brothers at See also:Port See also:Clarence at a depth of 376 yds .

Phoenix-squares

In Cheshire the surface-water trickling through the overlying strata dissolves the salt, which is subsequently pumped as brine, but at Middlesbrough the great depth and impermeability of the strata precludes this, so another method has been resorted to . A See also:

bore is made into the salt, and lined with tubing, and this See also:tube where it traverses the salt is pierced with holes . Within this is hung loosely a second tube of much smaller dimensions so as to leave an See also:annular space between the two . Through this space the fresh surface water finds its way, and dissolving the salt below rises in the inner tube as brine, but only to such a level that the two columns See also:bear to one another the relation of ten to twelve, this being the inverse ratio of the respective weights of saturated brine and fresh water . For the remaining distance the brine is raised by a See also:pump . The fresh water, however, as it descends rises to the surface of the salt, tending rather to dissolve its upper layers and extend superficially. so that after a time the superincumbent soil, being without support, falls in . These interior landslips, besides choking the pipes and breaking the communication, often produce sinkings at the surface . The same inconvenience is See also:felt in the environs of See also:Nancy, and a similar one produces on a larger See also:scale the sinking and subsidences at Winsford and Northwich . In the See also:United States extensive deposits and brine springs are worked, and also incrustations (see above) . Canada also is a producer . South America possesses several salt deposits and brine springs . See also:Asiatic Russia is very abundantly supplied with salt, as likewise is See also:China; and See also:Persia is perhaps one of the countries most abundantly endowed with this natural and useful product .

In See also:

India there is the great salt range of the Punjab, as well as the Sambhur Lake, and salt is obtained from sea water at many places along its extensive seaboard . The termination "wich " in See also:English place-names often points to See also:ancient salt manufacture—the word " wich " (See also:creek, bay; Icel. vik) having acquired a special sense in English usage . In See also:Germany the various forms of the non-See also:Teutonic words Hall, Halle occurring in place-names point in the same way to ancient salt-works . Rock-salt is the origin of the greater part of the salt manufactured in the world . It occurs in all degrees of purity, from that of See also:mere salty clay to that of the most transparent crystals . In the former See also:case it is often difficult to obtain the brine at a density even approaching saturation, and See also:chambers and galleries are sometimes excavated within the saliferous beds to increase the dissolving surface, and water let down fresh is pumped up as brine . Many brine springs also occur in a more or less saturated See also:condition . In cases where the atmospheric conditions are suitable the brine is run into large tanks and. concentrated merely by See also:solar heat, or it may be caused to trickle over faggots arranged under large open sheds called " See also:graduation houses " (Gradirhauser), whereby a more extensive surface of evaporation is obtained and the brine becomes rapidly concentrated . After settling it is evaporated in iron pans . The use, however, of the " graduation houses " is dying out, as both their construction and their See also:maintenance are expensive . The purer rock-salt is often simply ground for use, as at Wieliczka and elsewhere, but it is more frequently pumped as brine, produced either by artificial solution as at Middlesbrough and other places, or by natural means, as in Cheshire and Worcestershire . One great See also:drawback to the use of even the purest rock-salt simply ground is its tendency to revert to a hard unwieldy See also:mass, when kept any length of time in sacks .

As usually made, white salt from rock-salt may be classified into two See also:

groups: (1) boiled: known as fine, table, lump, stoved lump, superfine, See also:basket, See also:butter and See also:cheese salt (Fr. sel fin-fin, sel a la minute, &c.); (2) unboiled: common, chemical, See also:fishery, Scotch fishery, extra fishery, double extra fishery and bay salt (Fr. sel de 12, 24, 48, 6o and 72 heures) . All these names are derived from the See also:size and See also:appearance of the crystals, their uses and the modes of their production . The boiled salts, the crystals of which are small, are formed in a See also:medium constantly agitated by boiling . The fine or stoved table salts are those white masses with which we are all See also:familiar . Basket salt takes its name from the conical baskets from which it is allowed to drain when first it is " See also:drawn " from the pan . Butter and cheese salts are not stove-dried, but See also:left in their more or less moist condition, as being thus more easily applied to their respective uses . Of the unboiled salts the first two, corresponding to the Fr. sel de 12 heures and sel de 24 heures, show by their English names the use to which they are applied, and the others merely depend for their quality on the length of time which elapses between successive " drawings, and the temperature of the evaporation . The time varies for the unboiled salts from twelve See also:hours to three or four See also:weeks, the larger crystals being allowed a longer time to See also:form, and the smaller ones being formed more quickly . The temperature varies from 55° to 180° F . One difference between the manui`acture of salt from rock-salt brine as carried on in See also:Britain and on the Continent lies in the use in the latter case of closed or covered pans, except in the making of fine salt, whereas in Britain open ones are employed . With open pans the vapour is See also:free to diffuse itself into the See also:atmosphere, and the evaporation is perhaps more rapid . When covered pans are used, the loss of heat by See also:radiation is less, and the salt made is also cleaner .

It has also been proposed to concentrate the brines under diminished pressure . In S . Pick's system a triple effect is obtained by evaporating in these connected vessels, so that the See also:

steam from one heats the. second into which it is led (see See also:Soc. of Eng., 1891, p . 115) . In Britain the brine is so pure that, keeping a small stream of it See also:running into the pan to replace the losses by evaporation and the removal of the salt, it is only necessary occasionally (not often) to reject the mother-liquor when at last it becomes too impure with magnesium chloride; but in some works the mother-liquor not only contains more of this impurity but becomes quite brown from organic matter on concentration, and totally unfit for further service after yielding but two or three crops of salt crystals . Some-times, to get rid of these impurities, the brine is treated in a large tub (bessoir) with lime; on settling it becomes clear and colourless, but the dissolved lime forms a skin on its surface in the pan, retards the evaporation and impedes the See also:crystallization . At times sodium sulphate is added to the brine, producing sodium chloride and magnesium sulphate by double decomposition with the magnesium chloride . A slight degree of acidity seems more favourable to the crystallization of salt than alkalinity; thus it is a practice to add a certain amount of See also:alum, 2 to 12 lb per pan of brine, especially when, as in fishery salt, fine crystals are required . The salt is " drawn " from the pan and placed (in the case of boiled salts) in small conical baskets hung See also:round the pan to drain, and thence moulded in square boxes and afterwards stove-dried, or (in case of unboiled salts) " drawn " in a heap on to the " hurdles," on which it drains, and thence is carried to the -See also:store . In most See also:European countries a tax is laid on salt; and the coarser as well as the finer crystals are therefore often dried so as not to pay See also:duty on more water than can be helped . The brine used in the salt manufacture in England is very nearly saturated, containing 25 or 26.% of sodium chloride, the utmost water can take up being 27%; and it ranges from 38 to 42 oz. of salt per gallon . In some other countries the brine has to be concentrated before use .

Saltmaking is by no means an unhealthy See also:

trade, some slight soreness of the eyes being the only See also:affection sometimes complained of ; indeed the atmosphere of steam saturated with salt in which the workmen live seems specially preservative against colds,