Another method of obtaining brine from a bed of rock-salt, and one frequently practised in France, is that of simply boring into the salt and letting fresh water run down the bore-hole, when it excavates a chamber for itself in the salt hy solution, and may be pumped up again as saturated brine. The boring for this purpose has to be of a tolerably laige diameter, say 8-10 in., and it must be tubed throughout 1) ith stout, well-riveted irou piping. Within this piping, descends the suction-pipe of a pump, this latter pipe being only 3i-4 in. diam.. and closed at the lower end, but having its sides pierced with numerous small holes for about 1-2 ft. from its lower extremity. A sufficient space is thus left between the two pipes for fresh water to fiud its way down to the bed of salt. It is usual to commence by sinking a well down to any water-bearing strata in the measures above the salt, and to commenee the boring only from the bottom of this well ; or a well is sunk alongside the boring. Fresh water frorn the upper strata or the surface is allowed to percolate from this well into the space between the tubing of the bore-hole and the suetion-pipe of the pump, and to descend to the salt, where it becomes converted into brine, and may be pumped up. The esta blishment of a brine-ehamber by this means is rather tedious, on account of the tendeney of the fresh water to rise to the top, and erosion to take place only at the immediate surface of the salt, which thus gets eaten out just where it meets the superineumbent bed of clay, morsels of whieh detaeh themselves, and, falling into the bore-hole, are liable to ehoke the pump. A year or more may thus elapse before any steady supply of saturated brine ean be pumped, much, however, depending on the nature of the bed immediately overlying the salt. If this be elay, mueh trouble aud inconvenience may be experienced ; whereas if a good firm bed of gypsum or anhydrite intervenes between the salt and the elay, as oceurs in the districts of the Meurtbe, all will be found to work successfully. Under these arrangements, the descending column of fresh water in the exterior pipe tending to counterbalance the ascendant column of brine in the suction-pipe of the pump to about of its height, the relative sp. grs. being as 1 to 1.20, the pump only has to do the work of elevating the brine through the remaining distance. Thus, with the bed of salt lying at a depth of 180 ft. from the level of the fresh water at the surface, the fresh-water column would tend to counterpoise and elevate the brine in the suetion-pipe of the pump to a height of 150 ft., so that the purnp itself would only have to lift or force the brine through the remaining 30 ft. In all cases, the brine when produced, whether by dissolving the roek-salt in tubs at the surface, or by extraction from the solution-chamber within the bed of salt itself, contains by far too mueh matter in suspension to be fit for immediate use. It is consequently allowed to clarify by subsidence in largo reservoirs (bessoirs) prepared for its reception.
Sometimes the brine, whether derived frora springs or otherwise, is not brought to the surface at a sufficient degree of concentration to be evaporated by artificial heat, without too great a con sumption of fuel. It then becomes necessary to concentrate the brine. The most economical mode of doing this is obviously spontaneous evaporation by exposure to the air ; and in plaees by the seaside where high winds prevail, and where land may be of but little value, large quantities of salt are economically produced, as already detailed, by this means. But in other places, this arrangement would be inconvenient, and other means of exposing the liquid to evaporation on an extended surfaee are resorted to. Such is the so-called " graduation" system invented by Abith in the 16th century, and still practised in a few plaees on the Continent. A graduation-house (Gradishaus) is generally. a huge shed, 300-400 yd. long, presenting one end to the prevailing wind, and open at bath ends. The interior is filled with rows of faggots ; the floor is a large flat reservoir or basin, and on the top, by means of pumps and other arrangements, the water is sprinkled profusely over the faggots, and in eourse of descending into the trough below, trickles over the sticks, and exposes a large evaporating surface. By several repetitions of this process, the liquor loses water, and a eoneentrated brine is the result. Fig. 1207 represents the general construction of a graduation-house. A description of that at Schbnebeck, one of the largest and most important establishments of this kind, will suffice, as the system is not required in England, and is becoming less used elsewhere. The building is 916 yd. long, aod 11-14 yd. high. It is filled with a double tier of faggots; presentiog a thickness of 5i-7/ yd. at its base, and 31-5i yd. at the top, consequently offering an immense superfieies for evaporation. The illustration shows the whole arrangement in profile, end on. a is the large reservoir for the salt water. It is excavated in the ground, and widens out at the top to c to cateh any drip the wind may carry away ; d e are merely stays to support the walls of the reservoir, and to sustain the building against the lateral pressure of the wind ; f is the wooden framework in which may be arranged 4 vertical walls or tiers of faggots. These faggots are made of white- or black-thorn, the branches of which are espeeially crooked and angular. The water is elevated by pumping to the
reservoir h at the top, which is so arranged that the outflow can be altered according to the way of the wind. The water is allowed to descend through two pipes, elosed or opened at will by the valves h, into the transverse pipe g ; thence it rises through the pipes, and flows out by cocks into pans, from the overflow of which it drips on to the faggots. Berthier calculates that the average evaporation in ordinary fine weather by this means at Moutiers, in Savoy, where cords are employed instead of faggots, the other general dispositions remaining the same, is 131,gal. for every sq. ft. of eord surface in 21 hours. At Kissengen, the sheds are nearly 11 miles long by 25 ft. high. The water is raised six times in passing from one end to the other of the building, and by this, its strength is raised from 2i to 17/ per cent. of salinity. Forbes bas calculated that here nearly 3 million cub. ft. of water are evaporated annually by this means. The first set of faggots aro stained brown by ferric oxide which encrusts them, and they all have to be changed every two yours or so, on acrount of a deposit of ealcintn carbonate (" thornstone") which coats them. By whatever means the strong brine is obtained, it needs evaporation to produce white salt.
In England, as already stated, the brine comes up fit for use at once. In and around Winsford, nre 35 salt-works, and 607 pans ; in Northwich, 30 works, with about 485 pans ; at Middlewieh, 13 pans ; at Sandbaeh, 68. At Droitwieb are numerous works, mostly, however, on a smaller scale, with the exception of Chapel Bridge and Coverscroft. In Cheshire, the brine does not rise spontaneously to the surface in sufficient quantity to feed the works, but has to be extracted by pumping. It lies, as has been stated, on top of the rock-salts, on the corrugated surface of which it forms pools, or " runs," as they are often called. A shaft or well is sunk to the brine level, and the ingress of any fresh water from the overlying strata is guaided against by careful tubbing. The brine is then raised to the surface by means of pumps worked by steam power. Tho surface of the bed of salt is reached at a depth of about 40 yd., and the arrangements for the sinking and tho pumping of the brine are so familiar RS to need no description here. Suffice it to say that as brine exorcises solveut and corrosive effect on lead, and an oxidizing action upon iron, the use of either of these metals is to be avoided, either for tbe pipes or for the body of the pump itself ; copper for tbe former and bronze for the latter aro most to be recommended. Iron pipes are, however, usually employed in Cheshire and Worcestershire. Whole tree-trunks of elm or pine have been and aro still occasionally employed, cut into short lengths, and joined together, and bored out as pipes, for conveying brine, and answer that purpose very well. In a few eases, tbe pump-shafts have been cartied into old rock-salt mines, which have thus been utilized as solution-ebambers, or reservoirs from which to pump brine. The strength of the brine obtained varies both with the loaility and the Benson. Tbe salt-makers say that the brine used in Cheshire contains about 2 lb. 10 oz. of salt per gal., but this is misleading. The writer is indebted to C. M. Blades, analytical chemist, of Nortbwieh, for first drawing his attention to the following facts connected with this question. INben salt was subject to a government duty, the excise officers were in the habit of estimating the strength of the brine by means of a " salinometer," a form of hydrometer graduated to indicate the amount of salt in lb. and oz. per gal., as shown at A, Fig. 1204. The old wine gallon then in use only contained 58,317 gr. of water, whereas the present imperial gallon weighs 70,000 gr.; but the salinometer used at that time is still retained by the manufacturers, while the uow imperial gallon is the only one now recognized. The indications of this hydrometer are consequently misleading, and when, guided by this instrunaent, the manufacturer states that a brine of sp. gr. 1.204, and representing 26 per cent. of salt, contains 42 oz. or 2 lb. 10 oz. to the gal., bis statement is erroneous. An imperial gallon of water weighing 70,000 gr. (10 lb.), an equal measure of brine of 26 per cent., and sp. gr. 1.204, should yield ou evaporation 50 oz. (3 lb. 2 oz.) of dry salt, and this may perhaps be taken as an average strength for the brines of the Cheshire district. Misguiding as this may be, it has not so far led to any serious inconveniences, as the salt-makers usually purohase the brine front the owners of pumping-stations, paying on the amount of salt actually obtained. A change, however, iu the mode of supplying brine is now taking place, and melere for registering the delivery are being introduced by several of the punapers, with a view to check the enormous waste hitherto existing. In future, therefore, t,o avoid errors and simplify calculation, the present system of graduation of the salinometer will have to be altered. The French use the hydrometer of Baume, or pdse-sel, which is constructed to indicate dire,ctly the percentage of salt in a given weight of brine, being graduated from 0 to 27. Twaddell's hydro meter indicates exactly oz. Av. of salt in the gal. of brine by the numbers engraved on its stern.