Kitabı oku: «The History of Salt», sayfa 3
CHAPTER IV
GEOGRAPHICAL DISTRIBUTION
Salt, fortunately for us, is a commodity remarkably easy to obtain; almost everyone knows it is in great abundance in the ocean,30 and there are inexhaustible supplies of it in the earth; it is also present in some rivers, and in no inconsiderable quantity. Mr. John Ashley, in the Quarterly Journal of the Chemical Society, in his “Analysis of Thames Water,” tells us the exact amount:
Composition of Thames Water at London Bridge in grains per gallon of 70,000 grains.
We may account for this great proportion of salts by the fact that the Thames collects its water from the drainage of comparatively soft and soluble rocks; we should also remember the vast amount of refuse organic and inorganic matter which is being continually thrown into this river; and we must also call to mind that it is nothing more or less than the main sewer which receives the ordure of the modern Babylon.31
We may naturally suppose that in those rivers which flow through sparsely inhabited countries, where there is little or no traffic, the amount of saline matter would be next to nothing, and probably not a trace would be discovered. In a river like the Thames, owing to the vast quantity of its shipping, the great percentage which Mr. John Ashley has given us need not afford the least surprise. Sea-water is deficient in its proper proportion of salt at the mouths of great rivers, where the volume of fresh water displaces that which properly belongs to the sea, and therefore a river does not obtain much saline matter from that source.
Before we pass on to consider the geographical distribution of salt, we will just cursorily glance at the position it occupies in the vegetable world. It is present in all plants growing near the sea, and in variable quantities in some of those which are in or near districts where the soil is mixed with salt; though its place is taken by potash when they grow inland. Dr. Balfour writes as follows: “Soda and potash occur abundantly in plants. They are taken up with the soil in combination with acids. Those growing near the sea have a large proportion of soda in their composition, whilst those growing inland contain potash. Various species of salsola, salicornia, halimœnenum, and kochia yield soda for commercial purposes and are called halophites (ἁλς, salt, and φυτὸν, plant). The young plants, according to Göbel, furnish more soda than the old ones. There are certain species, as Armeria maritima, Cochlearia officinalis, and Plantago maritima, which are found both on the seashore and high on the mountains removed from the sea. In the former situation they contain much soda and some iodine; while in the latter, according to Dr. Dickie, potash prevails and iodine disappears.”
Soda being present in those plants growing near the sea, and potash in those which are inland, are two points well worthy of notice, and which we will now discuss. The number of vegetables which are cultivated near the coast shrink into insignificance when compared with those which grow inland; and naturally the markets are supplied with inland produce on account of a larger supply, therefore the consumption of those vegetables containing potash is in the same ratio. This being unquestionably the case, we ought, on that account alone, to use salt freely with our vegetable food in order to supply that which is absent, arising from the difference of locality and dissimilarity of the atmosphere. I shall enter fully into the relation salt bears to vegetable food while it is going through the process of digestion further on, when we come to consider the effects which food salted beforehand has upon the system when continued for any length of time, with little or no variation, which dietary is supposed to be the sole cause of the attacks of scurvy on board ship.
The sea is that grand reservoir which supplies the earth with its fertility; and the air and sun are mighty engines which work without intermission to raise the water from this inexhaustible cistern. The clouds, as aqueducts, convey the genial stores along the atmosphere, and distribute them in seasonable and regular proportions through all the regions of the globe.
With what difficulty do we extract a drop of perfectly sweet water from this vast pit of brine! Yet the sun draws off, every moment, millions of tons in vaporous exhalations, which, being securely lodged in the clouds, are sent abroad sweetened and refined, without the least brackish tincture or bituminous sediment; sent abroad upon the wings of the winds to distil in dews and rain, to ooze in fountains, to trickle along in rivulets, to roll from the sides of mountains, to flow in copious streams amid burning deserts and populous kingdoms, in order to refresh and fertilise, to beautify and enrich, every soil in every clime.
Though the ocean is salt, yet certain seas do not contain so much as others; my reader must not therefore conclude that the chloride of sodium, or salt, is equally diffused in sea-water, for the atmosphere receives a larger or lesser amount by reason of evaporation. Dr. Draper writes that the “temperature of the Mediterranean is twelve degrees higher than that of the Atlantic, and since much of the water is removed by evaporation, it is necessarily more saline than that ocean.”
It is said that the southern seas are slightly more salt than the northern, the reason for which phenomenon has not been, as yet, satisfactorily explained.
It is strange that salt should determine the colour of the sea, and that for centuries the cause of this peculiar natural phenomenon of the ocean should have been a closed secret even to men of science. Even from the earliest times, the origin of this marine peculiarity has attracted the attention and wonder of navigators; yet, strange to say, it has only been discovered within the last few years. The many expeditions which have been despatched by the Governments of England, Germany, and others, for the express purpose of oceanic discovery, have been the means of solving a question which has perplexed all races of seamen from the time of the Phœnicians, and which astonished Columbus on his voyage to the Indies.
These recent scientific investigations have proved that the proportion of salt held in solution by sea-water determines its blue or green appearance, and also its specific gravity; consequently, when the water is blue, we may conclude that it holds a much greater proportion of salt; when it is green, it is indicative that there is a decrease.
There is one phenomenon which is peculiarly interesting. There are two kinds of ice floating in the Arctic and Antarctic seas – the flat ice and the mountain ice. The one is formed of sea-water, the other of fresh. The flat or driving ice is entirely composed of salt water, which, when dissolved, is found to be salt, and is readily distinguished from the mountain or fresh-water ice by its whiteness and want of transparency. This ice is much more terrible to mariners than that which rises in lumps. A ship generally can avoid the one, as it is seen at a distance; but it frequently gets in amongst the other, which, sometimes closing with resistless force, crushes the doomed vessel to pieces.
The surface of that which is congealed from the sea-water is not only flat, but quite even, hard, and opaque, resembling white sugar, and incapable of being slid upon.
Salt is found in variable quantities in different countries, and in various conditions; in one part it may be found as a huge mountain, in which there are dark and lofty caverns; in others it is deposited in marshes and lakes, and in others in deep mines, many hundreds of feet beneath the surface of the earth.
In some countries there are vast quantities of rock or fossil salt. Salt has been divided into three kinds: native or rock salt; common or sea salt, also called white-salt; and bay-salt. Under the title of bay-salt are ranked all kinds of common salt, extracted from the water, wherever it is dissolved by means of the sun’s heat and the operation of the air. If sea-water is evaporated by means of a gentle heat we also obtain what is known as bay-salt. Common salt, or sea-salt, or white-salt, which is extracted from the sea, is composed of hydrochloric acid, saturated with soda, and is found in salt water and salt-springs, also in coal and gypsum-beds. “The sea itself, if desiccated, would afford a bed of salt five hundred feet thick, one hundred for every mile.”
In England, and especially in Cheshire, there are large salt-mines, at Nantwich and Middlewich, which have existed ever since the Roman occupation of Britain; and in the year 1670 the Staffordshire salt-mines were discovered, and accordingly excavated. Those in Cheshire have been renowned for centuries; their great extent is such that the surface has subsided on account of its being undermined for so many miles.
“In England, the Trias is the chief repository of salt, or chloride of sodium; and brine-springs, which are subterranean streams of water impregnated with salt from percolating through saliferous strata, are abundant in the great plain of the red marls and sandstones of Cheshire. The salt, however, is not uniform in extent, but occupies limited areas.” The saliferous strata of Northwich present the following series:
Droitwich, in Worcestershire, which is situated nearly in the centre of the county, has been celebrated for the production of salt from its brine-springs from the time of the Romans, who imposed a tax on the Britons, who, it appears, worked the mines; and also made salt a part of the pay of their soldiers’ salarium, or salary.32 Ever since, this inexhaustible fountain of saline water has continued flowing up, and yielding salt in undiminished quantities. It is very likely that the manufacture is coëval with the town itself; but it was not till the year 1725 that the strong brine for which it is now celebrated was discovered. From one spring, even, the enormous amount of one thousand tons of salt are obtained every week. At the depth of thirty or forty feet is a bed of hard gypsum, about one hundred and fifty feet in thickness; through this a small hole is bored to the stream of brine, which is about twenty-two inches in depth, and beneath this is the rock-salt. The brine rising quickly through the aperture is pumped into a capacious reservoir, whence it is conveyed into iron boilers for evaporation. It is supposed to be much stronger than any other in the kingdom, containing above one-fourth part its weight of salt. “One of the shafts is sunk to a depth of nearly five hundred feet, and passes through four layers of salt, eighty-five feet in aggregate thickness. Some of the beds of salt in Cheshire are from seventy to one hundred and twenty feet in thickness;” and it is sometimes so hard that it requires to be blasted with gunpowder.
In those districts where the marls of the Trias are covered by other beds, and the salt-springs force their way through the superincumbent deposits to the surface, these solutions of the chloride of sodium undergo a chemical change, acquiring other properties, and are then called mineral waters. The Cheltenham waters originate thus.33 Beneath the town of Cheltenham lie the Triassic deposits, the reservoir of the rock-salt and brine-springs, which generate the mineral waters, and from which they derive their saline ingredients. In their passage to the surface they go through various modifications, by reason of the superincumbent beds of Lias, which are impregnated with iron pyrites and the sulphate of lime. From the analyses of these waters, it appears that their principal constituents are the chloride of sodium (muriate of soda), or sea-salt, and the sulphates of soda and magnesia. Sulphate of lime, oxide of iron, and the chloride of magnesium are present in some wells only, and in much smaller quantities. Besides these ingredients, iodine and bromine have been detected by Dr. Daubeny, who instituted experiments to ascertain whether these two active principles, which the French chemists had recently discovered in modern marine productions, did not exist in mineral waters issuing from strata formed in the ancient seas. As the saline springs of the red marls rise up through the Lias they undergo certain chemical changes. From the decomposition of the sulphate of iron which takes place, a vast quantity of sulphuric acid must be generated, which, reacting on the different bases of magnesia, lime, etc., contained in the strata, forms those sulphates so prevalent in the higher or pyritous beds of the Lias; the oxide of iron being at the same time more or less completely separated. By this means the mineral waters, which are probably mere brine-springs at the greatest depths, acquire additional medicinal qualities as they ascend to the places whence they flow. At the same time, it must be borne in mind that fresh water is continually falling from the atmosphere upon the surface of the Lias clays, and percolating through the uppermost strata.34
The medicinal properties which are peculiar to these mineral waters will be considered further on, when we come to discuss the action of salt on the system, in health and disease, and the restorative results which are due solely to its instrumentality.
The salt district is in the line which joins the Severn, the Dee, and the Mersey, and doubtless once consisted of lakes flooded at every tide, which, drying at certain seasons and at low tides, deposited beds of salt, from Droitwich in Worcestershire, through Nantwich, to the Mersey; brine-springs flowing over beds of salt, or rock-salt, being found at different places on the entire line.
In the year 1863 a bed of rock-salt was discovered near the mouth of the Tees, at Middlesborough, and also on the Durham side of the river. The boring at Middlesborough showed that it was about 100 feet in thickness. Of late, borings have been made near Port Clarence, on the Durham side, but with what result I am not informed.
Scotland, as well as Ireland, is deficient in the more recent formation; for salt, as well as chalk, does not occur. Both are entirely absent; but geologists inform us that at one time chalk did exist, judging from the presence of flints in considerable quantities in Aberdeenshire, which they say affords unequivocal evidence of the former presence of cretaceous strata now integrated; and they account for it thus: the soft chalk being exposed to the action of the rain and storms, has been gradually washed away, while the flints which were embedded in it still remain. If this hypothesis is correct, that at one time chalk existed and is now absent, we may by inference, though we possess no evidence, presume that salt likewise, at some period or other, was present in this part of the United Kingdom. Chalk being entirely composed of the accumulation of marine shells ground to impalpable powder, which has been gradually consolidated, and being very rich in organic remains of shells, star-fish, sponges, fishes, and lizards, must have been deposited by sea-water, as its various ingredients indicate; therefore, during its deposition, salt, if originating from sea-water, must of necessity have left some marks characteristic of itself, in conjunction with the chalk; both being, more or less, intimately connected with sea-water, though the formation of one may not have been simultaneous with the formation of the other.35
In our lately acquired “gem of the sea,” Cyprus, there have been found extensive lakes of salt near Larnaca, the capital, so that this liberally-abused island possesses at least something which may prove of pecuniary value to its present owners. Being for several centuries under the benighted rule of the Turk, this staple of commerce has been entirely neglected, so as not to have been of the slightest use to the inhabitants or to the greedy pachas.
In the south of Western Australia there are vast salt marshes which only require to be worked so as to become the means of enriching the colonists, and indirectly attracting emigrants to this hitherto unprofitable portion of a dependency of England. The principal, which is called Lake Austen, is 1400 feet above the level of the sea.
Salt is also to be found in our Indian Empire, in Rajpootana and elsewhere, and is of considerable value to that country, especially while it remains in the hands of the enterprising European; according to Mr. Wynne, there is a salt range which extends from Kalabagh to a point north of Tank. After acquainting us with its geographical position, he says: “The coincidence between the physical features and the geological structure of the ground is intimate, the axial lines of the mountains carrying on the Salt Range feature being also axes of anticlinals lying for the most part along the scarped acclivities presented towards the Indus plains. These plains are part of the great quasi-desert flat over which the Indus has in past times capriciously wandered towards the Arabian Sea. Whether they are due in any degree to marine explosion is uncertain, though the sea may very possibly once have covered the low ground in question. The ridges of the Salt Range, as they exist at present, doubtless mark the same great later, or post-tertiary, period of mountain-forming activity, in which originated not only the remainder of the Salt Range, but also the Western Himalaya and the Suliman and Afghan mountains.” When we come to consider the geological bearings of salt, and its presumed origin, and other points in connection with it, I shall again revert to this highly interesting paper of Mr. Wynne’s.
In the Deccan, half-way between Bombay and Nagpur, there is a very remarkable salt lake. It is a circular hollow, about one mile across, and from 300 to 400 feet deep, having at the bottom a shallow lake of salt water without any outlet. This hollow, I must tell my reader, is ascribed by scientific men to a volcanic explosion.
There are so many lakes of salt, which are completely isolated and so many miles from the sea, that it is next to impossible to account for their existence if we do not ascribe them to volcanic action. If they are situated in low-lying districts, we may justly presume that at one time the sea must have been present, or that the deposition must have resulted from occasional, or tidal, overflow of salt water; but when they are many miles from the coast, and many feet above or below the sea-level, then they may be due to volcanic agency; and we shall find further on several other salt lakes of variable depths or altitudes which would seem to corroborate this hypothesis. The sea is undoubtedly a most formidable agent in the disintegration of land, and often destroys whole tracts, forcing its resistless waves into the interior of continents, and then, owing to some unexplained cause, retiring to its original boundary. This may take centuries to complete, for revolutions effected by nature are not accomplished speedily, unless there is some sudden spasmodic upheaving, arising from earthquakes or storms. In 1282, the isthmus uniting Friesland with the north of Holland was totally destroyed by violent storms. In our own country a similar phenomenon occurred in the year 1475, when a large tongue of land at the mouth of the Humber was entirely broken up and carried away by the sea. In 1510 an irruption of the Baltic formed the Frische-Haff, an opening 6000 feet broad, and from twelve to fifteen fathoms in depth. The eastern coast of England is continually receding, owing to the encroachment of the sea. The rate of encroachment of the sea at Owthorne, in Yorkshire, is reckoned at four yards in every year, and several villages have been swallowed up by the ocean; and in like manner the cliffs of Norfolk and Suffolk are suffering a continual decay.
Though the sea is so destructive an element, it is also an agent in the reproduction of land. The rocks and sand washed away from one place are conveyed by tides and currents far into the sea, and are deposited in strata, and then, in course of time, form shoals and banks, which subsequently become promontories and islands. Alluvial land has thus been formed, and in a similar way have many of the stratified rocks been deposited; and as animals and plants have been carried away and imbedded in the deposits of rivers, or floods, so at some future period, though countless ages may elapse during the process, will such animals and plants be discovered deposited in these newer strata, just as we find organic remains in the older rocks. The gradual deposition of strata has been the work of an incalculable period of time, but the process may be traced every day in the sections of marine estuaries and lakes. Owing to this continual receding of the land in one part, and elevation of land in another, there is an incessant change, from which, though occupying many ages, and proceeding so slowly that it would be unobservable were it not for accurate investigation, we may easily conjecture that what is now land may at one time have been the bed of the ocean, and where the sea now sweeps with overpowering fury, there may once have been meadows and forests. The salt lakes, if not originating from volcanic force, no doubt are the remains of the great ocean, which, when it receded, left here and there, in what once were luxuriant valleys, large reservoirs, indicating that in bygone ages it had covered the land.
In Germany, Spain, Italy, Hungary, and Poland, there are extensive mines of rock-salt, and also in various other parts of Europe.36 There are also large mountains wholly composed of this fossil salt, two of which are in those provinces of Russia known as Astrakhan and Orenburg; and in the Crimea salt is said to be daily accumulating in the inland lakes. In Asiatic Russia there are extensive beds of salt, near Lake Indur, in lat. 48° 30´, long. 69°. The Caspian Sea, called by the Turks “Cozgoun Denghizi,” “the sea of crows and cormorants,” is “a great salt-water lake,” according to Dr. William Smith, though Dr. Lemprière says that “its waters are sweet.”
The most interesting salt-mine is that of Wieliczka, near Cracow, in Galicia; it has been celebrated for centuries, and has been worked for the last six hundred years. This wonderful mine is excavated in a ridge of hills at the northern extremity of the chain which joins the Carpathian mountains. When the stranger reaches the mine there bursts upon his view a little world, the beauty of which is scarcely to be imagined. He beholds a spacious plain containing a kind of subterranean city, with houses, carriages, and roads, all scooped out of one vast rock of salt, as bright and glittering as crystal, while the blaze of the lights continually burning for the general use is reflected from the dazzling columns which support the lofty arched vaults of the mine, which are beautifully tinged with all the colours of the rainbow, and sparkle with the lustre of precious stones, affording a more splendid and fairy-like aspect than anything above ground can possibly exhibit. In various parts of this spacious plain stand the huts of the miners and their families, some single, and others in clusters, like villages. They have very little communication with the world above them, and many hundreds of persons are born and pass the whole of their lives here.
Through the midst of this plain lies a road which is always filled with carriages laden with masses of salt from the furthest part of the mine. The drivers are generally singing, and the salt looks like a load of gems. A great number of horses are kept in the mine, and, when once let down, never see daylight again.
Such is the marvellous salt-mine of Wieliczka, which is more renowned on account of its magnitude, its age, and the weird and almost supernatural aspect it presents to the visitor, than any other. Those subterranean palaces, with their magnificent appurtenances, their fantastic occupants, and other dreams of the imaginative, are not more strange or astonishing to the fascinated reader of romance than this extraordinary, glistening, cavernous, mineral city, with its numerous lamps, its crystallised walls, its roads, and the plaintive songs of the drivers as they drive their horses through its sunless thoroughfares, presents to the eyes of the surprised traveller.
There are valuable mines of salt in France, and in Greece, near Missolonghi, but these have no special points of interest connected with them.
In Abyssinia there are extensive and inexhaustible beds of salt, which is used in quite a different way from what it is in other countries, for little bars of it are circulated in place of small coin; but it is only when it reaches the Amhara and Galla districts that it becomes valuable.37
In other parts of the African continent there are large mountains of rock-salt, and those of Tunis and Algiers are especially notable.
Salt is also to be found in Asia, in large mountains, in marshes, and in lakes, to some of which I have already alluded. In the north of Persia there is a large salt desert, and near Ispahan there are quantities of rock-salt. The island of Ormuz, in the Persian Gulf, almost consists of fossil salt; it is indeed so very plentiful that the atmosphere is completely charged with it, so that the dwellings of the inhabitants are encrusted with a tolerable thick layer, giving them a peculiar glistening appearance; this phenomenon is owing to the small particles of salt continually floating in the air and rising from the ground, much in the same way as we see dew deposited on the top of a garden wall or on a lawn after a hot summer’s day.
We learn from Herodotus that there was a salt lake in Phrygia, in Asia Minor. “Having so said, and fulfilled his promise, Xerxes continued his route onwards. After passing by a city of Phrygia, called Anaua, and a lake out of which salt is produced, he came to Colossæ, a large city of Phrygia.”38 I have previously alluded to the Dead Sea and the interesting phenomena which it presents; due south of it is the Valley of Salt.
There are salt springs and springs from inflammable gas in China, in long. 101° 29´, lat. 29°, near Thibet; and there is a large salt lake possessing the strange name of Tsomoriri, many feet above the level of the sea, in Western Thibet.39 “The Chinese bore well through the rocks, and prepare the salt by firing the gas of others, so that one heats 300 kettles by gas-fire.” The celestials, with their habitual aptitude and industry, have obtained this salt for many centuries, and simply by this ingenious method.
As a fact illustrating the value of salt in Siberia, I may as well mention that in our own country a ton of salt is sold for fifteen shillings, whilst on the Yenesei river as much as fifteen pounds is given for the same quantity. The Muscovite we thus see is as acutely alive to the beneficent results of a free use of salt as a dietetic, as we English, and it would seem as if he were more so.
In some countries remote from the sea, which are devoid of salt-mines, and where the water is not impregnated with it, the inhabitants, aware of its usefulness, have a method of extracting it from the ashes of vegetables. This fact would certainly seem to indicate that salt has been used by various nations, as if mankind had an intuitive knowledge of the benefits arising from the use of salt, and that consequently, if there were no lakes containing it, or mountains from which they could procure it, they were determined to obtain it if even by artificial means.
As an illustration of the presence of salt in places distant from the sea, I need only refer to the Great Salt Lake of Utah, on the shores of which stand the Mormon city. Long before the founder of the Latter Day Saints thought of establishing a quasi-religious community, travellers who had the temerity to wander over the wild prairies of the Oregon, the home of the bison and the hunting-ground of the Indian, and who explored the secrets of the then unknown land of the “Far West,” were struck with amazement at the glistening aspect of the surface; for in many places it was covered over with an impure kind of salt, apparently a combination of muriate and sulphate of soda,40 or more probably an impure form of the chloride of sodium. On tasting the water which had collected in numerous little pools of no more than a few inches in depth, they found it so bitter and pungent that it acted on the mucous membrane almost as powerfully as a corrosive poison. This large tract of country was at that time teeming with life, for they daily saw vast herds of bisons, and frequently came upon the hidden towns of the prairie-dog; in fact, wherever they went, they either crossed the path of these wild denizens of the plain, or else the sky was darkened by innumerable flocks of birds. The district was wonderfully healthy, and totally free from malaria or other causes generative of disease; the Indians, too, were splendid specimens of humanity; they had not as yet been tainted by too close a proximity with the so-called superior civilisation of the white man, neither had they been so unfortunate as to have fallen a prey to the vices and diseases which generally accompany the humanising European.
On the pampas of La Plata, which is the treeless abode of the wild horses of South America, there are several salt lakes, not many miles distant from the river Quinto, and over these boundless wastes thousands of wild cattle and horses gallop at pleasure, and afford an inexhaustible stock of game for the lasso of the fearless and expert Gaucho. Now it is a well-authenticated fact that those diseases which are so destructive to the horses and cattle of Europe are almost unknown in these regions. I do not mean to assert that these salt lakes of La Plata account for the exemption which this district enjoys from equine diseases; but there is no doubt that the exhalations from them purify the atmosphere, and that their influence extends for many miles because of the open nature of the country. As a natural result, the whole region is constantly kept in a healthy state; for air, charged with the chloride of sodium, must of necessity act as a preventive to everything inimical to health, and pure air we know (though how few really know what that blessing is) is of a paramount importance in the rearing of cattle. The foot-and-mouth disease, comparatively, has never played such havoc as it does in Europe, and pneumonia, which is almost intractable to treatment in this part of the world, and which is frequently fatal when it is complicated with inflammation of the pleura, hardly ever appears in these parts, where stables and farms are not far off from being rudimentary in construction, and would appear to an English farmer, accustomed to the cosy-looking farmsteads of his own country, very ill-calculated for successful farming, and not at all adapted for bringing his cattle and horses to perfection; yet it is just the reverse, for there is no other part of South America so well fitted for the breeding of cattle, and there is no other locality, whether in the Old or New Worlds, so completely free from disease as the open pampas of La Plata.
