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M. Margneritte, of Paris, well-known as a distinguished chemist, has discovered a valuable mode of purifying rock and sea salt. The latter is, for the most part, delivered for consumption in such a state that it is frequently desirable to rcHne it. When this is to be done, it is necessary to dissolve it again, and cause it to evaporate in a pan or boiler. The means which M. Margueritte proposes for purifying it consist simply in fusing the raw salt, and keeping it for some time in a state of tranquil fusion, decanting it into hot molds, or letting it cool slowly ; in this manner all the impurities are separated from the mass in fusion, and are eliminated by crystallization by the dry process, which corresponds with crystallization by the wet process. Two layers are produced, of which the lower one is formed of foreign matters. When the cooling takes very long, the salt crystallizes in form and aspect quite analogous to that assumed by rock salt. Like the latter it is transparent, presents an equal purity, and possesses the same physical properties. When the cooling is rapid or sudden, the crystals are confused or indistinct, less transparent, and less voluminous. In either case, the mass previously crnshed or pounded by submitting it to the action of a mill, is then separated in varions sizes by means of sieves. This operation could be advantagQously applied to pnrifying rock salt. This salt, which is perceptibly purer than sea salt, nevertheless contains earth and foreign matters, which give it a brown, green, and sometimes a red color, and render it unfit for immediate use. If the raw rock salt be fnsed on the hearth of a furnace, for example, and maintained in a state of tranquil fnsion for some time, all the impurities settle to the bottom, and the coloring disappears by the oxydizing action of air under the influence of heat; and if care be taken to keep the current of air moist by a discharge of steam, the whole of the chlorid of magnesium is decomposed, and the mass can then be poured off to cool, or allowed to cool slowly. A mass of crystals, more or less transparent, according to the rapidity of the cooling, is so obtained, which are very white and pure.
