SULPHUR 79 



the element can be of commercial value, it is necessary 

 to free it of all impurities. In Sicily where the largest 

 deposits occur, this is done by digging out the sulphur 

 and heaping it into large piles. The mounds are then 

 covered with sod and dirt and a fire is started under- 

 neath. 



The heat produced causes the sulphur to melt, and 

 it is then run out into troughs. Naturally much of 

 the sulphur is burned and passes off as sulphur dioxide. 

 Thus a large percentage of waste results. This loss 

 has now been overcome by heating the substances out 

 of contact with the air. 



The method is first to place the ore in heaps in 

 closed vessels and to heat it until the sulphur melts and 

 thus separates from the earthy substances. The low 

 melting point of sulphur makes this possible. It is 

 then further purified by heating it in closed iron ves- 

 sels having ducts leading into a cooling chamber made 

 of bricks. The sulphur vaporizes; when the vapor 

 conies into the cooling chamber it is suddenly cooled, 

 and some of it collects as fine powder on the Avails of 

 the chamber. This form is known as flowers of sul- 

 phur. Most of the sulphur vapor condenses to the 

 liquid form and falls to the bottom of the cooling 

 chamber. It is then run into molds where it hardens 

 into the cylindrical shaped rods known as roll sulphur. 

 The method used in the United States consists in 

 sinking into the sulphur beds four concentric iron 

 tubes. The inner tube is one inch in diameter; the 



