MINING OF ROCK SALT 37 



to the top of the breakers, similar to those used in coal 

 mining and from ioo to 145 feet above the surface of the 

 ground. To separate the lump salt from the finer material 

 the contents of the cars are dumped on a set of iron bars, 

 which permit all the salt to fall through into the crusher 

 below except the lumps, which are loaded onto other cars 

 and run down an incline to the ground, where they are 

 stored, usually in the open air, for shipment. The finer 

 material passes through the crushers on to sieves and from 

 the latter into the bins. Of the crushed and sifted salt 

 there are four kinds according to size. The lump salt is 

 mainly used for stock, the other grades for the same pur- 

 poses for which sea or solar salt is used. 



The quality of the mine salt may be learned from the 

 following analysis of an average sample (A) and perfectly 

 white salt (B). 



A B 



Moisture a trace a trace 



Insoluble 0.7430 per ct 0.0584 per ct 



Sulphate of lime (calcium sulphate). . 0.4838 " " 0.0793 " " 



Calcium chloride 0.0180 " " 0.0358 " " 



Magnesium chloride 0.0546 " " 0.0888 " " 



Pure salt 98.7006 " " 99.7410 " " 



TECHNOLOGY OF MANUFACTURE 



The salt of commerce is derived from sea water, from 

 natural brine, from artificial brine made by dissolving rock 

 salt, and directly from the latter by crushing and grinding. 



Salt is derived from sea water in three principal ways : 

 by solar evaporation in pits, by the aid of frost and by heat. 

 The separation of salt from sea water by solar evaporation 

 is carried on along the Atlantic coast of Europe, i. e. in 

 Portugal, Spain and France as far north as 48° of latitude. 

 On the Mediterranean coast the separation of salt from sea 

 water is carried on in France and Spain, in Italy on the 

 Tyrrhenian and Adriatic Seas, and by Austria on the shores 

 of Istria and Dalmatia. In these regions the sea water is 

 allowed to flow into a series of tanks formed by excavation 



