SULPHUR. 205 



liquefied sulphur is raised through other pipes to the surface by means 

 of compressed air. Crude sulphur generally contains from 2 to 4 per 

 cent, of earthy impurities. 



Sublimed sulphur, Sulphur sublimatum (Flowers of sulphur). 

 Obtained by heating sulphur to the boiling-point in suitable vessels, 

 and passing the vapor into large chambers, where it deposits in the 

 form of a powder, composed of small crystals. Sublimed sulphur, 

 when melted and poured into round moulds, is known as roll-sulphur 

 or brimstone. 



"Washed sulphur, Sulphur lotum, is sublimed sulphur washed 

 with a very dilute ammonia water, and then with pure water ; the 

 object of this treatment being to free the sulphur from all adhering 

 sulphurous and sulphuric acid, as also from arsenic compounds which 

 are sometimes present. 



Precipitated sulphur, Sulphur prsecipitatum (Milk of sulphur). 

 Made by boiling one part of calcium hydroxide with two parts of 

 sulphur and thirty parts of water, filtering the solution, adding to it 

 dilute hydrochloric acid until nearly neutral, washing and drying the 

 precipitated sulphur. 



By the action of sulphur on calcium hydroxide are formed calcium polysul- 

 phide, calcium thiosulphate, and water: 



3Ca(OH) 2 + 12S : : 2CaS 5 + CaS 2 O 3 + 3H 2 O. 



On adding hydrochloric acid to the solution, both substances are decom- 

 posed and sulphur is liberated : 



2CaS 5 + CaS 2 O 3 + 6HC1 = 3CaCl 2 -f- 3H 2 O + 12S. 



While the above equation gives the final result, the decomposition takes 

 place in stages, thus : 



CaS 5 -f 2HC1 = CaCl 2 + H 2 S + 4S 

 CaS 2 O 3 + 2HC1 = CaCl 2 + H 2 S 2 O 8 

 2H 2 S + H 2 S 2 8 = 3H 2 O + 4S. 



Precipitated sulphur differs from sublimed sulphur by being in a more finely 

 divided state, and by having a much paler yellow, almost white color. 



Experiment 13. Mix in a beaker about 10 grammes of powdered sulphur, 20 

 grammes of slaked lime, and 200 c.c. of water, and boil until the liquid has a 

 deep brown color. Renew the water that is lost by evaporation occasionally. 

 Note that the color deepens as boiling is continued. This is due to the poly- 

 sulphide of calcium, which is colored. Finally, filter into a large flask or 

 beaker, wash the filter, dilute to about half a liter, and add dilute hydrochloric 

 acid until the solution is nearly neutral. Note the milk-like appearance of the 

 liquid. Let the sulphur settle fully, decant the liquid, filter and wash the sulphur, 

 and let it dry in the air. Compare its appearance with that of lump sulphur. 



