SALT 



747 



upon each side of the ash-pit (see figs. 1750 and 1751), into which cold air is admitted 

 by the flue q, r, where, becoming heated, it is conducted through iron pipes, , and 

 thence escapes at t, into the stove-room. Upon both sides of the hot flues in the store- 

 room, hurdle-frames, u, u, are laid, each of which contains 11 baskets, and every 

 basket, except the undermost, holds 60 pounds of salt, spread in a layer 2 inches thick. 

 v, v, shows the pipes by which the pan is supplied with graduated brine. 



Description of the Steam-trunk in Jig. 1753. In front of the pan a, a, there are two 

 upright posts, upon which, and in holes of the back wall, two horizontal beams, b, b, 

 are supported. The pillars c, c, are sustained upon the bearers, d, d. At e, e, a deep 

 quadrangular groove is made in the beams, for fixing down the four boards which 

 form the bottom of the steam-way. In this groove any condensed water from the 

 steam collects, and is carried off by a pipe/, to prevent it falling back into the pan. 

 Upon the three sides of the pan not in contact with the wall, there are three rows of 

 boards hinged upon planks, b, b. Behind the upper one, a board is hung on at g, 

 upon which the boiled salt is laid to drain. The two other rows of boards are hooked 

 on so as to cover the pan, as shown at h. Whenever the salt is sufficiently drained, 

 the upper shelves are placed in a horizontal position ; the salt is put into small 

 baskets, and carried into the stove-room, i, k, is the steam-trunk ; I, m, is a tunnel 

 for carrying off the steam from the middle 



of the pan, when this is uncovered by 1753 



lifting the boards. 



In proportion as the brine becomes 

 concentrated by evaporation, more is 

 added from the settling-reservoir of the 

 graduation-house, till finally small crys- 

 tals appear on the surface. No more 

 weak brine is now added, but the charge 

 is worked off, care being taken to remove 

 the scum as it appears. In some places 

 the first pan is called a schlot-pan, in 

 which the concentration is carried only 

 so far as to cause the deposition of the 

 sludge, from which the same solution 

 is run into another pan, and gently 

 evaporated to produce the precipitation 

 of the fine salt. This salt should be 

 continually raked towards the cooler and 

 more elevated sides of the pan, and then 

 lifted out with cullender-shovels into 

 large conical baskets, arranged in 

 wooden frames round the border of the 

 pan, so that the drainage may flow 

 back into the boiling liquor. The drained salt is transferred to the hurdles or 

 baskets in the stove-room, which ought to be kept at a temperature of from 120 to 

 130 Fahr. The salt is then stowed away in the warehouse. 



In summer the saturated boiling brine is crystallised by passing it over vertical 

 ropes ; for which purpose 100,000 meters (1 10,000 yards) are mounted in an apartment 

 70 meters (77 yards) long. When the salt has formed a crust upon the ropes about 

 2^ inches thick, it is broken off, allowed to fall upon the clean floor of the apartment, 

 and then gathered up. The salting of a charge, which would take five or six days 

 in the pan, is completed in this way in seventeen hours, and the salt is remarkably 

 pxire, but the mother-waters are more abundant. 



The mother-water contains a largo quantity of chloride of magnesium, along with 

 chloride of sodium and sulphate of magnesia. Since the last two salts mutually de- 

 compose each other at a low temperature, and are transformed into sulphate of 

 soda, which crystallises, and chloride of magnesium, which remains dissolved, the 

 mother-water may with this view be exposed in tanks to the frost during winter, 

 when it affords three successive crystalline deposits, the last being nearly pure sulphate 

 of ooda. 



The chloride of magnesium, or bittern, not only deteriorates the salt very much, 

 but occasions a considerable loss of weight. It may, however, be most advantage- 

 ously removed, and converted into chloride of sodium, by the following simple 

 expedient : Let quicklime be introduced in equivalent quantity to the chloride of 

 magnesium present ; double decomposition will take place, resulting in the precipita- 

 tion of magnesia, and the formation of chloride of calcium ; the latter will then react 

 upon the sulphate of soda in the mother-water, producing sulphate of lime and chloride 

 of sodium, the former of which, being sparingly soluble, is almost entirely separated. 



