SALT 



121 



while in some parts of the Alps they come from 

 rocks of Jurassic age. Similarly in North America 

 saliferous formations occur on several geological 

 horizons. Thus, the salt-works at Syracuse, New 

 York, and in the neighbourhood of Gouerich on the 

 Canadian side of Lake Huron, are in the well- 

 named ' Salina group ' of the Upper Silurian. 

 Brine-springs also rise from the Carboniferous 

 strata of Michigan, Ohio, and Virginia, while a 

 thick bed of rock-salt of apparently Cretaceous age 

 occurs in southern Louisiana. 



Not infrequently rock-salt occurs in considerable 

 abundance at the surface ; some of these accumula- 

 tions are of quite recent formation, while others 

 are of great geological age. Thus, at Cardona 

 (Montserrat) in Spain rock-salt forms hills some 

 400 and 300 feet in height the deposits being 

 probably of Cretaceous age ; and similar masses 

 occur near Orenburg in Russia, and in the Punjab. 

 Superficial saline deposits are met with covering 

 extensive areas in many more or less desert regions, 

 where they evidently indicate the sites of dried-up 

 lakes and inland seas of comparatively recent age. 

 As examples may be cited the rock-salt deposits 

 of the Kirghiz Steppes, those near Lake Urumiah, 

 and in various parts of South America. Salt lakes 

 from the bottoms and shores of which rock-salt is 

 obtained are met with in many regions, both in the 

 Old and New Worlds. Thus, it in collected in 

 Cyprus, Melos, the Crimea, and the Aral-Caspian 

 area; and many saline lakes, pools, and marshes 

 occur in the great western region of North America. 

 Even in dry warm regions where no salinas may 

 happen to exist, an efflorescence of salt not infre- 

 quently covers the ground after rains the salt 

 having doubtless been derived by capillary attrac- 

 tion from the underlying subsoils and rocks. 

 Rock-salt also occnre as a product of sublimation 

 in volcanic regions, from which it lias been inferred 

 that much of the steam emitted by volcanoes has 

 come from water introduced by underground fissures 

 from the sea. 



When brine is pumped up to the surface it is run 

 into cisterns or reservoirs situated at a higher level 

 than the evaporating pans, into which it descends 

 through pipes. These pans are large shallow iron 

 vessels, heated either by coal-fires placed beneath 

 them or by other means, such as waste steam. With 

 a high heat and a short time in the pan a fine salt 

 is produced ; with a comparatively low heat and a 

 longer time in the pan a coarse salt forms. Agitation 

 of the brine tends also to produce a fine salt. Brine 

 boils at 228 F., and it is at this temperature that 

 ordinary table-salt, called also ' lump or ' lumped ' 

 salt, is produced. At about 165 F. what is called 

 ' common ' salt U obtained ; large-grained salt forms 

 at between 130 and 140 F. ; and fishery -salt, also 

 large grained, at from 100 to 1 10" F. The salt 

 erjretaUUe* on the surface of the brine in the pan, 

 floats about a little, and then falls to the bottom, 

 leaving the surface free for a fresh crop of crystals. 

 Twice or thrice in twenty-four hours fine salt is 

 Mi awn from the pans, which are kept nearly full of 

 brine, by raking it to the side and lifting it out with 

 perforated scoops. It is then put into moulds called 

 'tubs, "and left for about half an hour to let the 

 water drain off, after which the shaped lumps are 

 put into a stove, where they remain till they are 

 quite dry. Sometimes even fine salt is not stoved, 

 and it is then railed butter salt or cheese salt. To 

 make salt of the largest grain the brine is left for 

 nearly a fortnight before removing the crystals. 

 In this process the ' bittern ' or magnesium chlor- 

 ide remains in solution after the common salt 

 separates. 



At different places around the British coasts 

 alt was formerly obtained by evaporating sea- 

 irater, and to such salt the name bay -salt (often 



used for coarse salt) properly belongs. In Spain, 

 Italy, and southern France the manufacture of 

 salt in this way is practised on a large scale. 

 Besides common salt sea-water contains much 

 smaller quantities of potassium chloride, mag- 

 nesium chloride and sulphate, calcium sulphate, 

 and more minute quantities of other bodies. The 

 water of the Mediterranean, which is slightly more 

 salt than the open ocean, contains 2 '72 per cent, of 

 sodium chloride. As the evaporation goes on cal- 

 cium carbonate separates first and then calcium 

 sulphate. When the water reaches the density of 

 between T22 and P31 sodium chloride separates 

 along with small quantities of other salts ; and 

 when the specific gravity becomes 1 '33 very little 

 of anything but magnesium chloride remains. 

 A series of shallow rectangular basins are usually 

 so arranged that the water can flow from basin to 

 basin, and when it has reached the lowest the 

 partially concentrated sea-water is collected in a 

 well. From this it is raised to the first of another 

 series of basins, and finally into the series where 

 the salt crystallises. The salt is then stacked in 

 heaps, which are protected from rain and left 

 for months to drain. This to a large extent gets 

 rid of deliquescent and bitter impurities. It 

 then contains about 95 per cent, of chloride of 

 sodium, in which state much of it is sent into the 

 market. 



In some northern countries sea-water, suitably 

 placed for the purpose, is frozen over in winter in 

 order to increase the proportion of salt in what 

 remains liquid, since the ice so formed is fresh. 

 The water is then evaporated by artificial heat till 

 the salt is obtained. The chief markets abroad for 

 British salt are India and the United States. To 

 the former country about 300,000 tons are now 

 annually exported, and to the latter 120,000 tons 

 were sent in 1889, or only about one-half the aver- 

 age quantity exported to that country a few years 

 before. It is estimated that London consumes 

 daily 1 1 tons of salt. 



Besides its universal use as a condiment, salt is 

 an all-important substance in the manufacture of 

 soda, hydrochloric acid being obtained from it in 

 large quantities in the process as a by-product. 

 It is also employed in the manufacture of soap and 

 for producing what is called a salt-glaze on stone- 

 ware. Agriculturists destroy slugs and grubs with 

 salt, and it appears to improve the fertility of soils 

 when mixed with certain manures. Brine is used 

 in the pipes of freezing-machines. Rock-salt is 

 carved into cups and vases in the Punjab, and it is 

 said that houses are built of it in certain very dry 

 regions, as in the Desert of Caramania, where this 

 material is abundant. 



The salt-tax was or is in some countries an im- 

 portant source of revenue, though it is recognised 

 by economists as one that presses unfairly on the 

 poor. The salt-tax of the ancient regime in France 

 is referred to at GABELLE. In modern Italy 

 tobacco and salt are government monopolies. In 

 British India the revenue from the salt duty comes 

 next in value to that from land and opium. In 

 Burma it is now 1 rupee per maund of 82| 11). ; else- 

 where (since 1888) it is 24 rupees. In Britain salt 

 duties were first exacted in 1702 ; the rate was 5s. 

 per bushel in 1798, during the great French war, but 

 was ultimately increased to 15s. per bushel, thirty or 

 forty times the cost of the article ! The duty was 

 finally remitted in 1825. Salt makers or salters 

 used in some parts of Britain to be, like colliers, 

 serfs (see SERF). For the value of salt in pre- 

 serving food, see ANTISEPTICS and PRESERVED 

 PROVISIONS. For the varying saltness of the sea at 

 various depths, see ATLANTIC, PACIFIC, SEA, &c. 



See J. J. L. Ration's Common Salf( 1879 ) ; E. M. Boddy 's 

 Hillary of Salt (1881) ; C. G. Gttmpel, Common Halt (1898). 



