296 CHLORIDES. 



yield, when mixed, a precipitate of chloride 

 of silver ; newly-formed oxide of sodium or 

 soda remains in solution. The latter unites 

 with the acid originally employed to dissolve 

 the oxide of silver. This is commonly nitric 

 acid. 



743. CHLORIDE OF SODIUM. COMMON 



From what _. i / i 



sources is com- SALT. Common salt is found in great 

 Obtained? abundance in Poland and other countries, 

 as Rock salt, which is regularly mined like 

 coal. It is also obtained by evaporating the water of 

 the sea or salt springs, in the sun or by artificial heat. 

 When the salt water is boiled down, the salt separates 

 in crystals, while the impurities remain in the small 

 portion of liquid which is not evaporated. These con- 

 sist principally of chloride of magnesium and other 

 salts. Contrary to the general rule, salt is equally solu- 

 ble in cold and hot water. 



744. When salt is to be made from 



How is salt , . . . 



produced from water which contains it in very small pro- 

 portion, it is a frequent practice in Europe, 

 to pump the weak brine to the top of large 

 heaps of brush, and allow it to trickle through them. 

 The object of the method is to produce a large evapo- 

 rating surface. The air, as it passes through the heaps, 

 carries away a large part of the water, and leaves the 

 salt behind. The strong brine which is collected below, 

 is then boiled down, as before described. The annual 

 produce of the salt spring at Syracuse, New York, ex- 

 ceeds 5,000,000 bushels. 



