SULPHUR AND HYDROGEN SULPHIDE 249< 



water in the outer pipes. But the air breaks up into small bubbles, 

 forming with the liquid sulphur an emulsion which has a lower 

 specific gravity, and this flows freely up a three-inch pipe which 

 surrounds the air pipe. The sulphur runs into wooden enclosures, 

 measuring 150 by 250 feet, in which it quickly solidifies. The 

 product is so pure that, for most purposes, no other treatment 

 is required. The output of Louisiana and Texas 500 tons a day 

 from each well and, in all, over 1,000,000 tons annually supplies 

 the whole demand of the United States, and could easily be 

 increased. 



A number of sulphates, such as gypsum (CaS0 4 ,2H 2 O) and 

 barite (BaS0 4 ), and several sulphides, such as galena (PbS), zinc 

 blende (ZnS), and pyrite (FeS2), are found in large quantities as 

 minerals. The last two sulphides are used in the manufacture of 

 sulphuric acid. 



Allotropic Forms of Sulphur. Sulphur appears in two 

 different liquid forms, and in two familiar and perfectly distinct 

 solid varieties. The two latter are called, from their crystalline 

 forms, rhombic and monoclinic sulphur. 



Physical Properties of Rhombic Sulphur. This form is 

 yellow, with specific gravity 2.06. Natural sulphur, roll sulphur, 

 and practically all of most specimens of flowers of sulphur are of 

 this variety, and are identical in all physical properties. Speci- 

 mens of natural sulphur often show the rhombic crystalline form 

 very clearly. All the forms of sulphur are insoluble inwatenand 

 all the crystalline forms are soluble in carbon disulphide^- Good 

 rhombic crystals are obtained from the solution (Fig. 10, p. 14). 



The rhombic form is stable when not heated above 96. If 

 kept above this temperature, it slowly changes into monoclinic 

 sulphur. 



Monoclinic Sulphur. This form is obtained most quickly 

 by first melting some sulphur (m.-p. 114.5), and then allowing it 



