The process is simple, and requires but little apparatus of any kind. The first condition for the establishment of a “saline” is a low, broad, level ground on the border of the sea, bay, or inlet, which can be protected by dykes or dams from the action of the tides. A shallow artificial pond, or reservoir is made near the sea, and, if possible, below the level of high tides: so that it may receive water from the sea at high tides, by means of flood-gates. When, however, it is above the sea-level, the water may be elevated by means of hydraulic machines. The bottom of the pond or reservoir must be laid out perfectly even, the soil must be clayey, to retain the water, and should be beaten hard and smooth. Its outline may be irregular, and its depth should be from three to six feet. Of course its size must depend on the extent of the “saline” which is to be established. In this reservoir the sea-water deposits its sediments, becomes warmed by the sun's rays, and begins to evaporate.

From this reservoir the partially concentrated brine is led by a canal to a series of “rectangular basins,” No. 1, from ten to sixteen inches in depth. These “basins” are divided into a series of compartments, by means of little cross banks, through which the brine flows successively, in a slow current, which can be regulated at pleasure. These “basins” should be carefully prepared like the “reservoir,” so as to retain water. Here, by the action of the sun and wind, the water is rapidly evaporated, and deposits a portion of its lime, in the form of sulphate. When the concentrated brine marks 15° to 18° of Baumé's hydrometer, it deposits a considerable quantity of sulphate of lime; and when it marks 25°, the whole of the lime is deposited.

From “basins” No. 1 the brine passes, in like manner, to another series of similar “rectangular basins,” No. 2, larger and more shallow, but more carefully constructed. In these “basins,” No. 2, the remainder of the sulphate of lime is deposited, and the evaporation is carried to such a point that the water becomes a saturated brine by the time it reaches the lower side of them. At this period the volume of the concentrated brine is greatly diminished, and, marking 25° of Baumé's hydrometer, is ready to be transferred to the “salting tables.”

From “basins” No. 2 the concentrated brine passes, in like manner, to a third and last series of similar “rectangular basins,” No. 3, called “salting tables.” These are smaller and shallower “basins,” carefully constructed, and divided into compartments communicating with each other, and the layer of water should not be more than three inches in depth. The point at which the brine has reached a sufficient degree of concentration to be introduced into the “salting tables,” is sometimes judged of by the water becoming RED, but the hydrometer is, perhaps, a more reliable indicator—it should mark 25° of Baumé. In the “salting tables” the brine soon begins to deposit salt, in the form of crystalline crusts, which are either collected with rakes as soon as they form, or allowed to accumulate at the bottom, until they form masses of several inches in thickness. The brine on the “tables” is renewed daily, or every two days, according to the evaporation; whilst the “reservoir,” as well as “basins” No. 1 and No. 2, are constantly supplied with fresh brine. The concentration of the brines in the “salting tables” must be carefully watched, and their density never allowed to exceed 28 1/2° of Baumé's hydrometer, otherwise a deposit of sulfate of magnesia (Epsom salts) would be formed, rendering the salt impure. The mother-liquors, as they are called, are run off as soon as they have reached the above density: it is usually necessary to draw them off three or four times during the season. When the salt has attained a sufficient thickness, it is broken up and piled upon the sides of the “tables” in large pyramids, which are covered with clay. In these heaps the salt undergoes a process of purification—the moisture from the clay, or from occasional rains, penetrates slowly through the mass, removing the more soluble foreign matters, and leaving the salt much purer than before. If the salt in these heaps is too much soiled to be sent into market, it requires a process of refining. For this purpose two methods are employed; the one consists in simply washing the crude salt with a concentrated brine, which removes the foreign salts, and a large portion of the earthy impurities. The other, more perfect, but more costly process, consists in dissolving the impure salt in water, and adding a little lime to precipitate the salts of magnesia, always present, after which the filtered brine is slowly evaporated, to obtain the large-grained salt used for salting provisions. When the “salines“ yield the coarsely crystalline “bay-salt,” there is no need of these refining processes.

At some of the French “salines” the concentration of the brines is carried as far as 32° of Baumé's hydrometer, and the salt separated into three qualities. Between 25° and 26° of Baumé, the brine deposits 25 per cent. of the salt extracted, which is kept apart, on account of its great purity, and sold at a higher price than the rest. In passing from a density of 26° to 28 1/2° of Baumé, 60 per cent. more of salt of second quality is deposited, and from this point to 32° the remaining 15 per cent. is obtained, somewhat impure and deliquescent, from the magnesian salts which it contains, but preferred for the salting of fish, on account of its tendency to keep them moist.

The “salines” are usually cultivated from March to September, so that the process is suspended during a large part of the year. But the French have recently introduced improvements, by which the works are carried on throughout the whole year, with an increase of the produce by about 50 per cent. During the months of autumn the evaporation is still carried on, though more slowly, and brine is furnished marking from 10° to 20° of Baumé. This is stored away in pits or large wells, where the diluting effect of the winter and spring rains is but little felt, and at the commencement of the warm season this brine is elevated into the evaporating “basins,” so that the summer's labors are commenced with concentrated brine, and the salt is all harvested in the months of August and September.

The foregoing method, when conducted on a large scale, constitutes the most economical means of making salt from sea-water. But the nature of our climate offers serious obstacles to the manufacture of salt by this process: first, on account of the large quantity of rain which falls; and secondly, from the great uncertainty of having dry weather after mid-summer, which is necessary during the deposition of salt on the “salting tables.” In the moist and rainy climate of Venice these difficulties are in a measure overcome, by so arranging the “salting tables” that in case of heavy rains the concentrated brines are rapidly run off into deep reservoirs or large wells, from which they are again elevated when the weather becomes fine.

The marsh lands, provided they have an underlying stratum of clay, might be prepared for extensive “salines.” In using sea-water of full strength, the proportionate area of the several evaporating “basins” may be as follows: Area of reservoir, 1/3 of total evaporating surfaces.Basins No. 1, 1/6 of total evaporating surfaces.Basins No. 2, 1/3 of total evaporating surfaces.Basins No. 3, 1/6 of total evaporating surfaces. When the water used is one-half the strength of that in the open ocean, the area of basins No. 3, the “salting tables,” need not be more than one-tenth of the aggregate evaporating surfaces. Whenever it is practicable, the different basins should be nearly on the same plane, so that the brine may flow from one series to the other, as its level is reduced by evaporation. But when it is necessary to construct the basins at different levels, the brines may be raised from one series to another by means of wooden drums, from eight to sixteen feet in diameter, moved by steam or horse power.

The “saline” at Baynas, in the South of France, covers an aggregate area of nearly 371 acres, and yields per annum 2,125 bushels (56 pounds to the bushel) of salt to each acre of evaporating surface. At other French “salines” the average yearly produce is about 1,594 bushels to each acre of evaporating surface. At the salt works of the Lake of Berre, near Marseilles, the brine is scarcely half the strength of sea-water, and yet the annual yield is 966 bushels of salt to each acre of evaporating surface. The average price of salt at the last-named “salines” is only five cents per bushel, but an outrageous impost upon it, amounting to ten times that sum, enhances the price to about fifty-five cents per bushel. At these works the “mother-liquors” are used for the production of large quantities of sulphate of soda (from which soda is manufactured), as also the salts of potash and magnesia.

The advantages of this method are: 1. That all the processes are conducted under shelter, so that the operations are independent of rainy weather. 2. That the space required for the works is comparatively small. 3. That the arrangements are not costly, and may be put up on any desired scale.

A large reservoir is constructed at some point conveniently situated for receiving the brine from the sea. From this the sea-water is pumped up into a large wooden cistern on the top of a tower 25 or 30 feet in height, from whence it is conducted to the graduation-house, to be concentrated.

GRADUATION-HOUSE.—This is a long, open frame building, the longest side of which is exposed to the prevailing wind of the locality. The floor of the building is made of a large clay basin, or of strong wooden planks, intended to collect the brine which has been concentrated by evaporation. The spaces between the frame of the shed are filled with bundles of twigs or fagots, so that the building looks like a vast wall of brush, 20 or 30 feet high, and from 100 to 1,000 feet in length. The pyramid of fagots should be ten feet thick at its base and six feet at its upper part. Under the ridge of the graduation-house, and consequently over the middle of the long wall of fagots, is a long wooden trough or spout, perforated with holes at small intervals, through which the sea-water flows from the large cistern on the tower. In this manner the weak brine is made to fall like a perpetual shower over the vastly extended surface of the fagots into the basin below, during which it is rapidly concentrated by evaporation. This partially concentrated brine is again pumped up, and undergoes the same operation successively, until it is sufficiently concentrated for boiling. The same brine is usually passed four or five times through the fagots before it is fit for boiling; it is then passed into a reservoir, and kept for the boiling operations. During these successive concentrations the fagots gradually become coated with a crust of the salts of lime, but one set will last about eight or ten years.

Of course it is best that this operation should be conducted during the warm season; in fact, when the temperature is below 27° Fahrenheit, a portion of salt is lost by the reaction of the sulphate of magnesia. But the boiling may be carried on at any season. In general, the brine fit for boiling should contain about 20 per cent. of salt, that is, should mark 20° of Baumé. The boiling process is the same as that indicated in the second method, and its cost will be as there estimated. By adding slaked lime to the reservoir of brine fit for boiling, the magnesia might be precipitated, and a purer salt obtained.