DISCOVERY 



32:; 



nium Chloride, is heated with hme to regain the vahiablc 

 ammonia so that it may be used again. Calcium 

 Chloride, which is formed in turn, is again probabh^ 

 heated, Professor J. M. Thomson states, to extract 

 the valuable chlorine by a secret process. 



Sylvinite 



In Alsace, near Mulhouse, there are some interesting 

 deposits of a mineral salt known as Sylvinite, which is 

 mined on a large scale, now, by the French. This 

 mineral is the source of the valuable potash-fertiliser, 

 and contains 35 per cent, of Potassium Chloride associ- 

 ated with rock-salt. This occurs at a depth of 1,600 

 to 2,300 ft. The deposits, like those in Cheshire, form 



the Potassium Chloride crystallises out while the 

 Sodium Chloride still remains in the solution as brine, 

 which is used again to treat a fresh supply of Sylvinite. 

 The Potassium Chloride crystals are subsequently 

 dried. Towards the end of the war, an artificial 

 process of extracting Potassium Chloride from the 

 flue-dust from blast-furnaces was instituted for the 

 manufacture of high explosives. 



Celestine 



A unique but 

 Celestine-digging. 

 surface at Yate. 



small English industr}- is that of 



This salt occurs in the Trias at the 



in Gloucestershire, and this is the 



Fig. 2.— wieliczk.\ sai,t mixes, galicia. 



The railway station on the third level. 

 (By courtesy of Sir Isaac Pitman &■ SonSy Ltd.) 



an ellipse with the longer axis running north-east to 

 south-west, that is to say that the deposits attain their 

 maximum thickness along this line, and thin out to the 

 north-west and south-east of it. Sylvinite exists in 

 two beds of 3 ft. to 8 ft. thick (locally up to 17 ft.) 

 belonging to the Tertiary period. The roof in the 

 mines is formed of hard clay, which renders the 

 workings watertight. The horizontal layers of the salt 

 are coloured in most beautiful shades of red, blue, and 

 yellow, probably due to different percentages of salts 

 which have separated out in the old salt-lake. The 

 concentration of the Potassium Chloride is effected 

 by immersing the Sj'lvinite in boUing Sodium Chloride 

 brine, which dissolves Potassium Chloride only. This 

 solution is gradually cooled for two or three days, when 



only important deposit in the British Isles. Its 

 commercial value lies in the fact that it contains 90 

 per cent, of Strontium Sulphate, which is converted 

 into Strontium Nitrate (by Nitric Acid) for the 

 manufacture of fireworks and red flares. Also, another 

 substance made from it, Strontium Hydroxide, attained 

 by. roasting the sulphate with coal and iron ore, is used 

 for separating sugar from beet-molasses. 



The small white crystals of Celestine are found 

 in masses 2 ft. thick in the red marly clay at a depth of 

 2 ft. to 10 ft. below the surface. In Sicily, where there 

 are large deposits, these crystals are coloured blue, a 

 fact which gave rise to its name. The deposits are 

 discovered by probing the clay with large iron rods 

 until they strike the stone. A pocket or layer is thus 



