Tho sulphate and chloride of potassium obtained from the kelp lye may be converted into nitrate by decomposition with nitrate of sodium. Sometimes, instead of fishing the chloride of sodium from the pans, a shallow kind of scoop is lowered into the liquor, the top just reaching to the surface of the lye. By the force of ebullition, the salt is projected into these scoops, which are hoisted up whon filled, the liquor draining back into the pan through a series of holes pierced just below the rim of the vessel.
The chief seats of the manufacture are, the west coasts of Scotland and Ireland ; Jersey, Guernsey, and Sark ; and, in France, Normandy, Brittany, and La Manche.
(3) Chloride of Potassium from Sea or Brine-Springs.—In sea-water, the salt occurs to an average amount of about parts in 1000. The process of extraction has been an industry of considerable extent for many years in tho South of France, and upon low-lying coasts where a hot sun may be depended on. The water is conducted iuto large shallow ponds, or " salt gardens," and allowed to evaporate. Chloride of sodium separates out, mixed with a certain amount of sulphate of magnesium. The mother liquors contain considerable quantities of chloride of potassium, chloride of sodium, sulphate of magnesium, and chloride of magnesium. Two processes are adopted to obtain the products from these liquors. By the old method, they are allowed to concentrate to 31° B., and are then run off into shallow ponds, where, during the day, a second crop of chloride of potassium is deposited, and during the night a mixture of salts—chiefly sulphate of magnesium and a double sulphate of magnesium and potassium. The mother liquors are once more run off into a third series of ponds, where a further crop of crystals are deposited— chiefly a double chloride of potassium and magnesium. This is treated after the manner of the potash salts '' from Stassfurth, dissolved in water by the aid of steam at 120°, solution being facilitated by agitation. In place then of the double salt the chloride of magnesium remains in solution, and the chloride of potassium crystallizes out. From the mixed magnesium and potassium salts, by redissolving and ieorystallizing, a double salt, is obtained, which is utilized in the production of carbonate of potassium by decomposition with chalk and small coal.
Great loss of liquor, and injury to the salts, result from the slow process of natural evaporation and crystallization. A newer and better method is that of Merle, termed the "mithode a vingt-huit degr:s." The mother liquors, after the first separation of chloride of sodium, are evaporated to 28° B., and then diluted with about 8 per cent. of pure water, to prevent a too rapid accumulation of chloride of potassium in the after processes. They are then passed through refrigerators, and reduced in temperature to 18°, when a double decomposition takes place between the chloride of sodium and sulphate of magnesium. Chloride of magnesium remains in solution, and sulphate of sodium (Glauber's salts) crystallizes out. Thus MgSO4 2NaC1 = MgC1, NazSO„ The crystals are removed, and the mother liquor is evaporat,ed to 36° B. (62° Tw.). During evapo ration, the chloride of sodium, hitherto held in solution, and various other salts, separate out, and are removed. The liquor is then run into crystallizing cones, where the double salt of chloride of potassium and magnesium is deposited, and is treated as the "potash salt," carnallite, already described.
Chloride of potassium has hitherto been extracted from the waste of brine-springs upon only an experimental scale. Various methods have been proposed, other than those already set forth in treating of the manipulation of sea-water ; but as yet they are only interesting to the chemist.
(4) Chloride of Potash from Beet-root Molasses.—The treatment of " vinasses," or beet-root molasses, to obtain carbonate of potassium has already been described. The charcoal, or schlempe kohle, obtained on calcination, contains about 16 per cent. of chloride of potassium, and upon lixiviating the mass, concentrating the solution, and couling, the chloride crystallizes out, and may be washed and dried. The salt thus obtained rarely tests beyond 75 per cent., and the production is carried on upon a very limited scale.
Chloride of potassium enters largely into the manufacture of saltpetre, alum, and chlorate of pota,11. From it is made, by decomposition with sulphuric acid, the greater part of commercial sulphate of potash, and it is used to a considerable extent as an ingredient of artificial manures.