Tho annexed table by Poggiale shows the lbs. of pure salt dissolved by 100 lb. of water at various temperatures : 15° (5° F.) dissolve 32.73 lb. 40° (104° F.) dissolve 36-64 lb.
10° (14° F.) 33-49 50° (122° F.) 36'98 5° (23° F.) 34.22 60° (140° F.) 37.25 0° (32° F.) ,, 35.52 70° (158° F.) 37.88 5° (41° F.) 35'63 80° (176° F.) 38'22 9° (48°- 2 F.) 35-74 90° (194° F.) 38-87 14° (57° 2 F.) 35.87 100° (212° F.) 39.61 25° (77° F.) 36.13 109°7 (229° F.) 40.35 According to G. Karsten, a saturated solution of salt at sp. gr. 25 contains 26-535 per cent. of NaC1, and saturated at a boiling temperature, it contains 28.225 per cent.
The boiling-points of salt solutions of various strengths are given by Storer thus: Salt is found as rock-salt in stratified beds, usually forming large, lenticular or rounded-oblong masses, imbedded in red clays or variegated marls, these being usually interstratified with gypsum or anhydrite. It is likewise one of the chief constituents of sea water, salt lakes, and brine springs, and occurs in small quantities in all rivers and springs. It is found in all surface soils, sometimes as an abundant efflorescence. Some desert regions of Asia, N. Africa, N. and S. America, and Aus tralia, appear to owe their sterility to this cause. But probably at no period of the earth's exist ence did the formation of salt deposits proceed with the same activity as during the Triassic, and it is in the New Red sandstone, Bunter sandstone, or Keuper, and in -the red or variegated marls of the Tries, that most rock-salt occurs. An idea that all rock-salt was referable to that epoch long prevailed amongst geologists ; but it is now generally admitted that, although salt is found most abundantly amongst Triassic rocks, and becomes rarer as we descend into the earlier strata, it occurs in all the so-called sedimentary rocks. It has not yet been found in granite, nor in any of the crystalline truly so-called primary rocks. In the N. counties of England, are frequent occur rences of brine-springs rising from the Carboniferous series. The Cheshire and Worcestershire deposits are considered by some to belong to the Permian, though most generally they are referred to the Tries. The salts of W. New York, and Goderich (Canada) are said to be of the Salina period of the "Upper Silurian. The deposits of the Vosges, Salzburg, and numerous others are generally admitted to belong to the Tries ; that of Bcx in Switzerland, to the Liss ; those of Wieliecska in Poland, and Cardona in Spain, as also some deposits in Algeria, are considered to be Cretaceous ; those of the Pyrenees, in the neighbourhood of Bayonne and Dax, and at Camarade, are probably Tertiary ; while the Dead Sea, Lake Elton, many other inland lakes, certain estuaries on the shores of the Caspian, the Limans of Bessarabia south of Odessa, the run of Cutch, and the bitter lakes ot the Isthmus of Suez, are instances of salt deposits now in actual progress. The last-named lies in a basin which was intermittently inundated by the Red Sea, the waters being evaporated, and beds of salt thrown down, between the successive incursions. At the time the Suez Canal was made, the formation was partially destroyed. Its layers are said to vary in thickness from to 71 in., and
it is estimated to contain 97 million tons of salt, and to cover an area of 66 million sq. yd. The oldest deposit of rock-salt known to exist, whose geological age may be said to be positively determined, is the Salt Range of the Punjaub, which may with tolerable certainty be referred to the Permian, while the deposits lately discovered at IVEddlesborough-on-Tees may also probably be referred to this period, as they immediately overlie the magnesian limestone.
Thomas Ward and Von Baer describe the salt formation now going on upon the shores of the Caspian. As at this part it fills with river deposits, a number of bays and gulfs become nearly separated from the main body of the sea ; when this occurs on the eastern side, where no rivers enter, and where the evaporation is great, these bays and gulfs soon become intensely salt. Near Novo Petrovsk, on the eastern coast, is a number of basins, presenting every degree of saline concentration. One of these still occasionally receives water from the sea, and has deposited on its banks only a very thin layer of salt. A second, likewise full of water, has its bottom hidden by a thick crust of rose-coloured crystals, like a pavement of marble. A third exhibits a compact iaaass of salt, in which are pools of water, whose surface is more than a yard below the level of the sea. A fourth has lost all its water by evaporation, and the stratum of salt left behind is now covered by sand. Here we have an instance of what must have frequently happened in the drying up of seas. On the same coast of the Caspian, is the Kara Bog,haz, an estuazy of considerahle extent, and nearly separated from the main body of the sea by a bank, through which there is a shallow inlet. The evaporation from the surface of this gulf is so great that current continually sets in to it from the main body of the Caspian, and as there is no return current, the water of the gulf is daily becoming more saline, and a salt deposit is being formed, which Von Baer estimates at the rate of 350,000 tons a day. Schleiden says that the Caspian is deprived of nearly 450,000 tons daily by this current, which rather increases the quantity ; Von Baer's estimate would give 127,750,000 tons per annum. These figures seem exaggerated, in face of the composition of the Caspian. For every ton of salt conveyed in, there must be 99 tons of water. In process of time, this large gulf will be cut off from the Caspian, and gradually leave enormous beds of salt. On the N.-W. of the Caspiao, but some 200 miles from it, are the remains of a similar gulf, Lake Elton, from which large quantities of salt are annually obtained. In 1805, Gobel bored at a distance of about 14. miles from its then shore, and found 42 distinct layers of rock-salt, the uppermost 4 in. thick, the lowermost 9 in. The deeper he went, the purer and more solid was tbe salt ; at the 100th layer (1 ft. thick), it was so hard that the iron tool broke. In time, Lake Elton will disappear like so many others, and its salt will become covered by sand and soil.